one o'clock
he said , with a short laugh ; `` remarkably strong and effective . '' `` Yes , '' assented the Inspector , `` it _ is _ pretty powerful , and it requires to be so , for it does heavy work and travels a considerable distance . The greater the distance , you know , the greater the power required to do the work and transmit the messages . This is the battery that fires two signal-guns every day at one o'clock -- one at Newcastle , the other at South Shields , and supplies Greenwich time to all our principal stations over a radius of three hundred miles . -- I sent the contents of one hundred and twenty jars through you just now ! '' `` That 's curious and interesting ; I may even say it is suggestive , '' returned the detective , in a meditative tone . `` Double that number of jars , now , applied to the locks of street doors at night and the fastenings of windows would give a powerful surprise to burglars . ''