810 Traxsactioxs of the American Ixstitute. 



uiue and a half ouucea, the center of gravity was two and a quarter 

 inches above. 



Another of this sort: the ball weighed ten pounds eight ounces, 

 and the rod thirteen pounds five ounces, the center of gravity was 

 found to be four inches above the center of oscillation. I tried a 

 wooden pendulum with an iron ball eight inches in diameter, but 

 quite thin, the ball weighing four pounds, and the rod and nuts 

 two and a half ounces; and found the gravity center just half an 

 inch abovel 'Tis true, but why, I cannot answer. Reid says every 

 mathematician knows it, but he does not say how they know it, and 

 this is what puzzles me, being no mathematician. 



To find the length of a pendulum that will make, say twenty 

 beats in a minute, we figure about after this fashion: 



20 39.2 60 



20 3.600 60 



400 235.200 3600 



29.4 inches. 



Having the length of a pendulum to find how many vibrations 

 it will give in a minute, divide the number 1411.200 by the given 

 pendulum and extract the square root of the remainder. As it 

 has been found impossible to make a pendulum that will make 

 unequal vibrations in equal times, it becomes necessary to have the 

 motor as perfect as possible. If teeth are not of proper shape, 

 pitches perfect, and every part well finished, the impulses will be 

 unequal, and the clock will not keep time. When the rod of St. 

 George's was set swinging, and settled down to a normal gait, a 

 mark was drawn on the floor. In about three months it has gained 

 graduall}', until it passes this line about one-eighth of an inch. 

 This would make the gain in the whole length about one inch. I 

 think it is the longest pendulum ever put up in this country. 



One clock I have not mentioned, although it is not by any means 

 the least among them. I speak of the Third Avenue depot. It 

 has twenty-four inches main wheel, a pin escapement, and about 

 twenty feet rod. It carries two dials, one illuminated on the 

 avenue, the other in the rear, and can be seen the whole length of 

 the stables and shops down to Second avenue. It is exposed to a 

 greater range of heat and cold than any clock I know of, being 



