“As a complete description of this might weary the reader, I will give only a general conception of its structure. As already implied, the lapse of time was to be marked by the flow of water, and the most obvious difficulty being to render this equable, I employed for the purpose a floating syphon. The tube, which was so fine as to pass only about three drops per minute, was stuck through a flat piece of cork, which floated on the surface of water in a tin can; and as the water issued from the syphon it dropped into another can, though of much smaller size, hung at one end of a balance; so that, as this latter can filled, it became heavy enough to bear its own end of the beam down, while the opposite end, being of course tilted up, struck the trigger, which, as in ordinary alarums, released the weight, thus setting the clapper in motion. Now the length of time required to give the counterbalancing weight of water depended, of course, on the amount of weight put on the trigger-beam; and this was varied according to requirement, principally by means of a sliding weight, hanging from the beam as from a common steelyard. This sufficed so far as quarter hours were concerned, additional means of some complexity being used for securing the observance of smaller portions of time. The end was that I could count on being called within three or four minutes of the time fixed upon. In its early days, however, I was sometimes annoyed by irregularity, and, upon careful inspection, I perceived that this was caused by dust, which, falling into the water, found its way into the syphon, and impeded the flow. To remove this inconvenience, I enclosed my alarum in a box, taking care also to change the water with sufficient frequency. I remember that on the evening when I first got the machine to work, not willing to leave my new light under a bushel, I fetched up half-a-dozen boys into the room where it stood, that they might see and admire. When I had explained the mechanism, and arranged for a _réveille_ at the end of a quarter of an hour, the boys sat down in expectation; and probably being over-worked, according to our practice at the time, one of them fell fast asleep. Great was my delight, and great the amusement of his companions, when, at the end of the time, this, the first person ever awakened by alarum of mine, started up with a sudden exclamation of surprise and alarm, showing that my little machine had effectually performed its duty. “I may here remark that for one machine that I executed there were many that I devised. Thus I find the following entry in my Journal about a year later:—