Add legend to geom_line() graph in r
<p>I've been trying to add legend to my ggplot, but failed miserably.  I tried the function <code>scale_colour_manual()</code>, but the legend doesn't show up. </p>

<pre><code>ggplot()+
geom_line(data=Summary,aes(y=Y1,x= X),colour="darkblue",size=1 )+
geom_line(data=Summary,aes(y=Y2,x= X),colour="red",size=1  )
</code></pre>

<p>My dataframe 'Summary' is as follows:</p>

<pre><code>  X           Y1           Y2
139 1.465477e+16 7.173075e+15
277 1.044803e+16 9.275002e+15
415 1.059258e+16 8.562518e+15
553 1.033283e+16 8.268984e+15
691 9.548019e+15 1.022248e+16
830 1.008212e+16 8.641891e+15
968 9.822061e+15 9.315856e+15
1106 9.948143e+15 9.178694e+15
1244 1.013922e+16 8.825904e+15
1382 9.815094e+15 9.283662e+15
</code></pre>

<p>Please advise me how to plot Y1, Y2 against X on the same graph and add a legend on the side.</p>