I said it before, I'm gonna say it again. And I'm sure you're gonna hear me say it again in the future another time because this is not the last move to be made. But this has been the craziest, the wildest, the busiest season when it's come to Raven's roster moves. Both on the active roster, on the practice squad, cause God has just been coming and going, oh, can't forget the COVID list too. Can't forget that one. But this season has just been crazy, crazy. Now, Adrian Ealy. He was an undrafted rookie free agent out of Oklahoma. I remember hearing so many people say, oh man, when they looked at film on him, that he looked so promising that Raven's possibly got a steal. They got a low risk potential high reward type of guy. And I was thinking, okay, hey, that's offensive line help. Just in case anything goes down, you know I'm with it all day. The Mortimeria, especially when it's quality, not just quantity, not just bodies, but quality. So then he ended up getting suspended. He got suspended for whatever reason. I'm not sure exactly what happened, but then he got released. Don't burn your bridges, my friend.  Or sometimes when a company gets desperate enough, even if that bridge was burning, you left on bad terms, that company will turn around and say, hey, what's up, buddy? What's up, big head, buddy? How you doing, buddy?  And Adrian Ili is back because the Ravens have signed him to their practice squad. But why would they sign him to their practice squad? For what? What's been going on? Well, he wasn't the only person that they signed to their practice squad. They also signed a center, Jimmy Murray. So they were very, very busy. Now, one of the reasons why they signed him to their practice squad, well, Tyree Phillips. We know in the game on Sunday, he went out with an injury, never came back. And after that, David Sharp, who was actually in an article back in what like four years ago, I believe, cause I forgot who sent it to me, but they were like, hey, look at this. And Ravens had actually posted an article about revamping their offensive line and David Sharp was somebody that they were looking at in the draft. They didn't draft them, obviously, but a full circle, right? Everything came back around and now he's on the squad. But David Sharp, who came in for Tyree Phillips at right tackle, he look good. He look good. And one of the things that he showed that was just, you can't teach. I know my guy Cam Newell appreciated his effort and heart as an offensive lineman.  You can have all of that stuff. But it doesn't mean you're gonna just automatically be a good offensive lineman. You gotta have effort and you gotta have heart. And you gotta really show like, hey, I'm willing to protect my quarterback. And that's exactly what David Sharp did. And we were all hyped over David Sharp. We were like, man, okay, even though Tyree Phillips went down, we'll be straight. And I know a lot of Ravens fans weren't the biggest fans of Tyree Phillips. And I was thinking, I remember last year watching, I'm like, okay, it's a struggle, but it's also a COVID year. It's a COVID year. So he's a rookie, give him a pass. Especially after he picked up that fumble and ran it for a first time.  But last year was a bit rough. So like, all right, next year, he'll have an off season, have a full off season regime and all that stuff. But this year has been rough too. So now with David Sharp being thrown in there, we were like, okay, all right, hey, hey, y'all, y'all boys, we got one. But then COVID said, nope, I got one. I got another one. David Sharp got put on the COVID list. My goodness, man, this COVID list right now, as of right now, I'm recording this at 938 Thursday morning. So it could change. Some people could come off, hopefully. And some people could go on, unfortunately. But right now, Snape McCrary, Sammy Watkins, Jalen Moore, Tristan Cologne Castillo, our center, a little backup center, David Sharp, even though he's on the practice squad, that was all right tackle.  You gotta leave him out there. He's gotta be the starter for these last three games. But now who knows, who knows? Since he's on the COVID list, but Justin Houston, he's still on there. Parnell McPhee, who just literally just got back. He's on there. Chris Boyd, Christian Welch, Justin Matabique, Chuck Clark, Chris Westry, Jimmy Smith, Gino Stone, Kevin Toliver. Wow, that's our COVID list. That is our, those are all guys who are on the COVID-19 list right now. We're running out of bodies. We're running out of bodies. I remember hearing Wink. Wink, oh man, he had probably the quote of the year yesterday in the presser because when he talked about just losing so many people, he said, I don't know if this is the NFL or if it's squid games.   That's probably an understatement because it's all about survival. That's what it is for the Ravens. And I mean a lot of NFL teams, but that's what it definitely is for the Ravens because the Ravens, there's some teams that got hit with some injuries. But then there's some teams that got hit with COVID. But there's no team that got hit with both so much like the Ravens. They got hit with everything, everything. And it's just, it's wild. Jeff Zreben said the Ravens, they currently only have 15 defensive players on the active 53 man rock, 15. You gotta put 11 out there every play. And you only have 15 players for defense right now.  And then you got, guys are gonna get, have to get called up from the practice squad. But 15, that's crazy. That is insane. Now, with Adrian Ealy and Jimmy Murray, this wasn't the only move that the Ravens made. If you still here just part of the video, you can just put in the comment section. Hashtag stash is over, baby. You ain't gotta put the baby part, but just hashtag stash is over. It's over. But what are we talking about? Stash over what? We remember early on in the season, I think it was in the Lions game. Well, actually, I'll take you even before that in the pre-season. We were thinking, I even take you before that. In the off-season, we were like, okay, what's our pass rush gonna be like? And I felt like that was the only position where we had so much unknown. Because if we had Adafi away, he was a rookie coming into the NFL. We had Tyus Bowser. We had Purnell McPhee.  It's just so much unknown there. We don't know how good or how bad it's gonna be. It's just up in the air. So then the Ravens ended up signing Justin Houston. And it was like, okay, let's go. But even before that, in the draft, they had also drafted this guy named Daylan Hayes, who a lot of Ravens fans forgot about. A lot of times I forget about him too. Not because he was a bad player, anything like that. No, because it was just, he got put on End of Reserves so long ago. But anyway, it was just so many unknowns. But then, yeah, they signed Justin Houston. It was like, okay, we got a veteran pass rusher who has been productive too. He's been productive. And this system, that production been going down there, buddy, buddy. Anyway, because this system is not a system that produces many sex.  Because you could have a nice pass right, but this system is just not one that produces many sex. Another conversation for another day though. But with Daylan Hayes, we called him my guy Hayes and Sensation, gave him the name Daylan Dip Hayes, because he had this dip and it was like, oh, I was like, ooh, okay, I love it, I love it. Love it, love it, love it. But then, I believe in the Lions game, he hadn't got much playing time in the first two games. I think he was actually inactive the first two games. But then in the Lions game, he was active for the first time and then he got hurt like on the second or third play of the game, of the whole game. And then they put him on IR. Andrew didn't look that bad, but we are no doctors, we are no experts or anything like that. But I forgot what type of Andrew they even said he had. But they put him on Andrew Reserve and you never heard about him, you never heard from him again. And a lot of people were like, ooh, stash move, it's stashin' him. It's just stashin' him, stashin' him for next year, stashin' him, put him away for now. All right, we'll see you next year. And we know the Ravens, Ravens love a classic stash move. They love it. But when you lose so many people throughout the season, when you can barely feel the team throughout the season, this is how you know Ravens are going through it because they even got to pull out from that stash, man. They say, oh, we got a stash over here? Oh, okay, let's get something from there. All right, Dalyne Hayes, come on back. That's how bad it is. They couldn't even stash that guy. They gotta take him off the stash. So we happy to see Dalyne Hayes back for sure. Cause again, we need all the bodies we can get. This thing rough, man. It's rough. So Dalyne Hayes has been activated and he can practice again. So welcome back, Dalyne. Now, in addition to that positive news, let's look at the positive players. Well, the guys who are actually negative players who tested negative for COVID so far, shout out to everything underscore Ravens on Instagram because they provided this list. And these are players that aren't injured and aren't on that COVID list. So Brandon Williams, Broderick Washington, Justin Ellis, that's from the defensive line. Linebackers, Patrick Queen, Josh Bynes, Malik Harrison, Tyus Bowser, Daphir Wade, Jaylen Ferguson, defensive backs, Anthony Avid, Brandon Stevens, and Laphine Kevin Seymour. That's our second day right now. And then we got guys on a practice squad. We just signed Darryl Worley, Blake Countess, Robert Jackson, Joe Thomas, Isaiah Mack, Leo McKenzie, Jordan Richards, Tony Jefferson, and Mazi Wilkins. So if Ravens could call up every single practice squad player this week, they would. They would. Because they would have no choice. They would literally have no choice but to. But we'll see what type of team the Ravens can feel this week. I mean, again, it's 9.45 AM. Practice is a bit later. So Lamar Jackson hasn't practiced all week. It's not looking like he's gonna play. No, we still got to see today if he practices. But what was the tell-all for me? Even though it's not necessarily the end-all-be-all when it comes to Lamar and when it comes to the Ravens, but what told me Lamar wasn't starting this week, and obviously in addition to him missing both practices on Wednesday and Thursday. And again, we'll see about today. But when the presser was announced and they said, oh yeah, the guys who are gonna talk, the Ravens coordinators, Greg Roman, Wink Martindale, Chris Horton, offense, defense, and special teams coordinate. Okay, cool, no problem. But they also said Tyler Huntley was speaking. And when I saw that, I said, oh, okay. They trying to let us know. They trying to let us know subtly. Well, kind of subtly. Because your backup quarterback just doesn't speak to the media that often. So it's not looking like Tyler Huntley is gonna be the backup quarterback. But hey, if Lamar practices today, things could change. I don't think it's gonna happen. I don't see it happening. But we'll see. You never know till you know. And I'm sure if he doesn't practice today, they will ride this whole, oh man, well, he doesn't need to practice to play. Well, we'll see. He'll be a game time decision, but we'll know. Anyway, team keeping clean. Love y'all, I appreciate y'all. And we are out.


So, welcome to IIT Bombay, I am Milindath Ray, I am a professor in mechanical engineering department at IIT Bombay and I give you all my greetings from IIT Bombay and our department. I teach thermodynamics in mechanical department, I teach actually the applied thermodynamics where I teach refrigeration, cryogenic engineering, air condition etcetera. I am going to be your teacher for the next two weeks and taking ahead from where you left from Professor Gayathonday. I know that you have already understood the first law of thermodynamics. I will be teaching you now properties of fluids, wherein we consider water as an important fluid. So, we apply the properties of water for different processes and apply that using first law of thermodynamics. We know that water is used in various power plants, we know water is used in heat exchanger for cooling purposes and therefore, we have to understand how do we design these devices for which we have to see the properties of water at different pressures and temperature, the properties of steam at different pressures and temperature. So, this is what I will teach you in this course related to water phase diagram, properties of water, steam tables, mixture of two phase mixture of water and steam etcetera. I hope you find this course interesting because for mechanical engineers this course is going to be very very important. At the same time what I am going to teach here in this course is going to be more and more practical. I am happy to be a part of this course and I hope that whatever I teach you, you understand it in a better way and please send your feedback when my two weeks get over after teaching properties of fluids. Thank you very much.


So as you guys may recall, I had a refrigerant leak on these rotolock style fittings. So what we've got is a new fitting for this here and what we're going to do is we're going to go ahead and just cut it back a little bit and put a new fresh piece of copper in there so when we're brazing straight to that steel that we don't have any problems with any contaminated metal or anything like that. And I got a new seal for over here. We're going to go ahead and recover the refrigerant first. Once that's done, we're going to remove some of the oil so that we can get it down to below the pipe level here. Now this one didn't have the quick fill fittings like the other one did. It had a filter in here. Something I just noticed as I took off the cap, I had a hellacious amount of refrigerant come out. But if you look at this, straighter core right there, look at that, I can catch up with my finger. They didn't put that thing in there very tight or as far as it should go.  Just there, you can't even hear it. So we're going to go ahead and pull that core out, but that's something to keep in mind. These caps are really for dust, unless you're using a brass cap, these are not meant to seal it. Yeah, this one right here is the same way. So there could have been one of our other leaks. I didn't pick anything up on it, but surely is it helping it none? So make sure those are in, they should be flush or at least seat them. They've got a torque wrench that you can use. I've never used it. They're kind of neat looking, but I haven't needed one yet. Generally, a little common sense in using two fingers seems to work. I'm kind of curious if it turns very much. Oh yeah, look at that. There, I just tightened it up to how I would do it. Look at it, it's completely flush right now. Same thing. I bet you with this one. Okay, there I'm on it, almost one, one and a quarter turns, look it's flush. Got to love it. That's something to keep the luck out for. So for right now, we're just going to go ahead and yank the valve core out. And then what we're planning on doing is we're going to go ahead and recover this and we're also going to replace the filter dryer and we will pull an evacuation on this. That was something I think a few people didn't realize. I wasn't saying on my last video, which I'll have a link up at the top here, it should pop up about now. I never meant to imply that, hey, here's a half turkey bake way of doing something. What it was meant to do was here's some common sense on how to speed this up without doing a bunch of unnecessary work. At no point was I trying to imply that you don't change filter dryers and you don't pull vacuums and all that. That would kind of go against about everything I've done on any of my videos. Sometimes they don't come out. What I've done in the past is open it and it'll blow it out. I'm not going to do that on camera, but if you got one stuck in there, you can actually sometimes blow it out, but be doggone careful. That thing don't come out of there and blast you in the eyeball or put a hole through the roof because that's basically a dart. So we've got the valve core tool here with the valve there coming through the filter dryer, protecting our machine, going from the three eighths line into the machine, which we're dropping down to quarter. I understand that coming into the top of the radiator slash condenser with the fan running, coming out of the bottom, hopefully liquid, coming out, Shrader core depressor removed, going to be going into the tank. You're going to see how well this works. Now, when we're finished, we got to keep in mind, it's usually 0.6 ounces per foot. I end up coming up with about almost a pound of refrigerants, what this thing's going to hold. So when I get done, I actually put a ball valve on the end of my three eighths hose. When I'm got as much out of it as I can get out of it and it's down to zero or negative, I should say, I'm going to valve this thing off, unhook it, hook it onto the input side, then use just a straight hose over to the tank and then blow the remainder into there. Basically recovering what's liquids left in the tank and the three eighths hose here. This is going to press this all in there to its maximum capacity because I think this unit holds 45 pounds in this tank maximum capacity, I believe it's 47. So luckily today it's not super hot or only, I don't know, I'd have to guess maybe 70 degrees out, something like that, 72. So we're going to go ahead and zero this thing out so we can monitor how much weight we're putting into it. We've already got the tank. As you can hear, I had it vacuated. So there's that.  And I just used a splitter here to run the fan there. Probably would help though if we open that up. There we go. There's just sucking it through. I had already purged my hoses all the way up to the tank, so that's why you heard what you heard. You can see the hose shaking from the liquid going through it. Now I would have recommended having another three eighths hose. I just don't have one. But like I said, I do have the straighter core pulled out of that. I'm going to give special recognition to one of my viewers that mentioned doing this. I'll put his name on right now. This is a pretty good idea. And you know, we generally have these laying around all the time. You probably could have got away with a smaller one. The surface area of this is a whole lot bigger than what's in the machine. While that's doing that, let's take a look over here and see what this thing held again. I kind of forgotten. It holds 43.3 pounds. So we'll make sure to put that back in when we get done. That way we'll know she's completely charged. We're at 15 pounds. This is where the machine shut off on the other rooftop unit that I recovered. And so far she's holding right in there at about three. As far as the tank, she's warm, but she's not blazing hot like before. Probably about 104. Yeah, 104 degrees is where we're at. So right now we're about 187, something like that. Still holding pretty good on the head pressure. Still holding about 360. Switched it to the liquid side here just to see if that helps stir it around a little bit. More heat has to rise up. So even though it's got the restrictor in there because of the dip tube. And far as temperature, we're 77 out here. So while we're waiting on this, I'll go ahead and show a little bit of video of me getting this coil cleaned up and getting this thing ready because it was in pretty rough shape. The fins were smashed a little bit and it was pretty dirty. So obviously our flow is important. So I went ahead and chemically cleaned it. We're about 160 there. Head pressure's up a little bit. We're almost about 400, 405. The temperature going in is 116 and it's coming out at 92. Yeah, this is a time saver, big time. I mean, not having to run a garden hose all the way over here. Not having to get a bucket of ice. Tank's gotten a little warmer, about 121 area here. Bottom of the tank, as you can tell, is a lot cooler at 102. So most of my heat is up here on the top. Which is kind of interesting. I almost can't help but wonder, did I restrict it to the point where it caused more issues? More flow, even in vapor, would probably get more flow through the condenser, which then would cool it more. Can't help but wonder if I didn't make a mistake by doing that. If you go back and watch my other video, I followed this little chart here they got, which I don't like. And I've already expressed that. But you look here, we've still got about 45 pounds of pressure on it. Still holding no more than 450 down there. But we've got 44 pounds, 10 ounces, so we're a little overcharged. So going by their chart isn't very accurate.  But that right here shows me that that chart there is not adequate. So I was not impressed with it and I'm definitely not impressed with it now. Because I mean, when I showed low, I had 14 degrees subcooling. This is going out of memory. But if I remember correctly, I still did not hit what they wanted on that chart. And so I would have added even more, which would have been overcharged the unit. So I am not impressed. We did it without having to run any water. Next time I'm going to try it off the top of the tank like I started originally and see if it makes a difference. But we got it all in there and I'm satisfied. That's great. Okay, so we've got a little bit of nitrogen on the system right now and we're going to basically purge out the oil to get that down to level or below, which we're not getting anything, which is not a good sign. Yeah, that wasn't thought out very well. So like I said, basically I wanted to get this below because they're about the same level and we're already below. So that oil is in the system somewhere.  We might add a couple of squirts to it.  It shouldn't be overly tight and this one up too. Like I said, we're going to replace both seals. The only one of these was leaking. Okay, so there's that metal. There we go. Thank goodness that went right in the pan. Holy mackerel. That had been bad. We've got the official Jim Petitiano bowl here. Jim, if you're watching these, man, people are always asking about you. It's time to come back to making videos and screw the haters. That's a fact, Jack. So wipe off any gunk we got here on. Same thing with this one. Luckily, there's no rust on it. We'll peel out those nylon washers out of there. Just got me a new tool by Yellowjacket for changing my gaskets.  But this little gizmo here, you put it on there and shove it right in. Now, it also comes with a pick. So the pick is what I need right now. But those are the gaskets it helps put on, which is pretty sweet. You put that on there like that and it shoves it right into the spot. They're only about 15, 16 bucks. I'll have some of those in my links down there if you guys want to help support the channel and buy those through the Amazon, same price as everything else. Just, I get a small commission off of it. Here's how that comes together, which is pretty slick. Just now I got me a neat little pick, so I can come in there and boom, how she comes. So we'll wipe that out real good and we'll put a new one in. We'll make sure we lubricate it when we do it. I'm going to try to cover this up with some tape, too, because I don't want that oil absorbent moisture any more than it has to while we've got the system open. One part is to make sure we get this figured out on how long it needs to be. I was going the wrong direction. Obviously, on the big stuff, it makes a little more of a difference. It's going to take 45% silver solder to raise dissimilar metals and the flux. So we're going to make sure we get her all cleaned up. The metal will heat up faster than the copper usually, so you just got to watch your patterns and watch your heat. You'll be able to see where it's going. We'll clean all this out here in a second. You can see all this time it's taken to do this. That's the reason why I put that over top of the plugs for the oil. You don't want it set in there absorbing the moisture anymore and you have to.  That's what your filter dryers for. Generally, you could pull forever. At least that's what they always taught us. Maybe things have changed. A lot of things have, but there's that. Okay, I haven't cleaned it up with a wire brush or anything, so you can actually see it. There's no carbon inside there at all. And other than a little flaking from the metal, which is the galvanized coating, there's only so much you can do about it if you've got to get it hot, I was able to pull it all in there and then put a little bead around the outside when I got done, but I made sure to pull it all the way up. As far as I could get it without overheating any worse than what I already did, and there you go. It's fully solid all the way around and should not be any leaks.  I just have this bad feeling that things aren't going to line up right, which it almost looks like they didn't get them lined up to begin with, which might be why it cracked. It's very possible when they were putting this together at the factory they didn't get this situated quite right. And then with the heat and the twisting and turning and the shaking and the vibration and all that could be why it leaked, because it, you know, it was leaking on the solder joint, braze joint. Well, we know exactly where it goes at.  Sometimes you've just got to think about it for a minute and how you want to do it. This is our front one to get the other side, so we'll flip it over for that. We're going to go ahead and get this one nailed into place now because they've already burned off my markings for my marker, so I don't want to lose that position.  Take off our tape that we put back on, got our rings, they're back on there right like that. Put a little bit of this oil that we had left over on that fitting there and get it to turn a little bit. Maybe put a little bit on that ring there. I'm sure these have a torque wrench setting, but I don't know what they are and they didn't put it in the instructions because, you know, they obviously didn't think it was that important. We're using an 8-inch wrench here, so we're not going to overdo it to the point where it caused an issue later, so I'm going to say that right there looks to be pretty good. We've got a pressure test on it right now, the sprayer fittings down. I don't see anything leaking, so that's a good thing. Everything looks good. System like this nearly takes a tank or more, but I thought it was worthwhile to try checking it before I pulled it back on it and then charged it up and found it. Everything out of my hose here. Make sure we got good clean liquid. This is not the same as fluid ounces, but it gets me close. I don't want to put too much in there because the system's probably got the oil in it. There's a little bit down here, but I don't feel as though we've lost that much. Okay, we're going to stop there and we're going to let the system run for a while. Then we may have to come back and double check it. I don't want to overfill it with oil or 25 ounces, plus the three we purged out, so 26-27 ounces. Okay, you guys have seen this a million times, so I'm not going to go into big details, but basically they don't have a suction port over here on this side, so I'm going off of the liquid and hot gas discharge of the compressor, and I'm going to put my micron gauge on the suction port over at the other side. You figure the liquid lines bigger than most systems freaking suction lines, so we're going to get pretty good volume out of it and we'll make sure we're getting it on the other side. So that's not been running very long and we've already bragged about these big blue hoses, but here we are way over here. We're already at 1900 already, so I'd say it's less than what, 2 minutes, 3 minutes? Not bad. So, we're going to go ahead and let this thing pull down. The biggest thing I wanted to do on this video is just kind of show you guys the new sub-cooler I built and to test it out, and you guys could watch and see whether it worked with me, because I wasn't sure if it was going to work or not, so in all reality I think it did really good. We crammed pretty much almost maximum capacity into the recovery tank there, which was great, and basically you got to see the rotor lock fitting being replaced and the oil being added to the system. Like I said, I'm going to need to come back in a few days and double check it to see where it's at. I can about guarantee you there's not that much that's been lost there on the ground, which I don't know if that's from a previous repair, which I assume might be the case, but I wanted to make sure there was some in there until then and we can always take it back out. So the nice thing about this flare to flare dryer we got going on here is I'm able to flip it around and build it coming out of the tank now, where if it was a male to female it wouldn't be so easy. So we bled the hose, we got it zeroed out here, and we're going to dump in and see how much will actually go in with the traditional method here, so we're just going to charge through the high side and see what we get. Wait until it hits high pressure, then we'll remove it, so we got that. Fairly go ahead and do it with the quarter inch hoses just so we can save any left over. You can see it's jamming quite a bit of liquid right through there, so if you skip your bubba, we are ready to roll. So it's running, running about 330 pounds ahead right there with a 105 discharge temperature, and when you come up to 105, which is this line right above 100, and you follow that down to 325, intersect them, you're above it, add if above the charge.  I mean everything's feeding right, my super heat, and everything was just fine when we checked it the last time. So we don't have an issue with a restriction, a bad TXV, or anything like that. We had good subcooling, I think we had like 14 before I even added anything to it. So, you know, in both stages are running, both compressors are running, well first stage is one compressor, second stage is the opposite compressor with the first one shut off, and then both of them running high stage, and we are in high, and it's been running for about 10 minutes or so, and head pressure is about as high as what it's gotten, which is also controlled by a variable fan control, it has an ECM control on the motors, a couple of them, or maybe all of them I'm sure, looks like it might be all of them, they got the little module on the back end of them, so I mean this isn't no cheap unit. So like I said, just a 22.5 ton, and I do not approve, I think that sucks, but what do I know? Other than that, that kind of wraps this one up, and I appreciate you guys taking the time to watch it, if you like it, and you want to see more like it, please give it a thumbs up. Leave me a comment down below, don't forget to subscribe, and click that notification bell, and we will catch you guys on the next one.


Learning objectives include various types of microscopes that include dark field, microscopy, phase contrast, microscopy, fluorescent microscopy, transmission electron, microscopy, and scanning electron microscopy. There are many others also, but we would go through only a few of these. In dark field microscopy, it is a variation of light microscope, where the light source is used with a different condenser. It is a special condenser that bends the light and throws the light through the specimen in a way that light basically does not, if there is no specimen here, the light would not pass into the object. So when the specimen contains the organism there, this organism would basically bend the light, and that bent light would enter into the objective lens. And the advantage of this dark field microscopy is that the field, other than the organism would appear as dark. So when the light strikes the organism, the organism would be lit. It would be looking like white against a totally black background. And that is the reason we call it dark field microscopy. The advantage of using this is that we don't have to stain the cells. Sometimes we use such microscopes like dark field, and there is another one, phase contrast, without staining the cells, because staining with chemicals kills the organisms. If we want to capture them alive or without disturbing their morphology, this provides a better tool. Another one is phase contrast microscopy. It also does not use any stain, and we can study the cells in vitro as live cells. The principle behind this phase contrast microscopy is that wave light rays, they have the light travels in waves. If the two waves, they follow each other in all aspects, like this is the peak of the wave, and this is the trough of the wave. So a trough follows the trough, a peak follows the peak. So what we call these two waves are in phase with each other. Here the two waves, you see the trough of this wave is almost superimposed on the peak of this wave. So these two waves are at 180 degree out of phase with each other. The same principle of this phase change is used in phase contrast microscopy. The organism, when the light rays passes through the organism, it is retarded by almost one fourth of the wavelength. And then in this microscopy, which is phase contrast, we have a special plate, which is called phase plate, where you could see that the depth or the size of the plate is not exactly the same at all places. Here you see it is smaller than this portion. So the light that passes through the specimen, when it passes through thicker part of this phase plate, it is retarded even more. And here, because it has to pass through smaller distance of the plate, it is not retarded as much. So the trick is basically in this phase plate, which creates a contrast because of the variation in the phases of these two waves. So this wave, when this passes through the specimen and through the phase plate is out of phase, one half wavelength. And this difference creates the contrast. And the advantage again is that we can use this microscope without staining the cells. Another version of the light microscopy is a fluorescent microscope, where a dye, a special dye that what we call them fluorochromes, they are used. These are substances that absorb short wavelengths of light but then emit longer, which is visible, wavelength of light. As you can see here, this is the image taken from a fluorescent microscope. Fluorochromes, which are dyes or substances, they are attached to antibodies. As here, these are antibodies. They're attached with these antibodies. And then these antibodies, because they are specific against different organisms, those microbes could be stained specifically by these antibodies. And as these antibodies have these tags, these dyes associated with them, when we visualize these images under the microscope, they would fluoresce. They would emit different lights, colored lights. Here is the diagrammatic presentation of a fluorescent microscope. It, of course, uses a UV light, ultraviolet rays, which is kind of blue light. It passes through a filter. And then there's a special mirror, which does not allow a shorter wavelength, which is here. This is a UV light. And when it strikes this mirror, it gets into the specimen. And here is the fluorochrome lying here. And when it strikes the fluorochrome, it gets converted into longer wavelength. And then this longer wavelength can pass through this mirror. And then the image could be seen by the viewer or by the person who is looking through the eyepiece. Here is, again, the same thing. There's a source of light, a UV light, of course, passes that light through. And then there's a dichromatic lens mirror, which allows longer wavelengths to go through. And the observer can see that image through the eyepiece. Another version, as I mentioned, that resolution basically depends on the wavelength. Electron microscopy has way higher resolution power. Because electrons have very, very short wavelength compared with the light. But the principle of electron microscopy is exactly the same as light microscopy. So there is a source of light. There is a source of electrons. So this is the wavelength. This is the wavelength. The difference is that this wavelength is much shorter. And resolution, as a result, is much higher. Electrons pass through electromagnets, which basically act like lenses in the light microscope. So they focus the electron beam. And the electron beam then passes through the specimen. And then this image is created here. Because this is electron microscope, we cannot see the electrons with our eyes. We need a phosphorous screen, like a TV screen. So the image basically is created on a screen by the bombardment of these electrons. The advantage is that the image is much, much bigger. We can resolve very small structures. And we can see them in detail. Another version is scanning electron microscopy. Here the source of short wavelength is, again, the electrons. The only difference is that the electron, when it strikes the specimen, they are reflected off the specimen. And these are reflected off rays of electrons, or waves of electrons, or electrons. They are collected by a detector, special detector, and amplified through the electronic circuitry of the scanning electron microscopy. And the image is found, is a kind of three-dimensional image. This is the advantage of scanning electron microscope. So you can see the organism in 3D. Here is the image of a stephalorius. These are spherical cells. And as you can see, they look like beads, beautiful beads. In summary, there is a host of microscope available for us to use or to see different organisms at different magnifications, some with staining and some without staining.