348 Mr. Scrymgeour's Experiments to determine the Influence 



tions than cylinders whose diameters are greater or less than 

 that size, I leave to those to determine who are better ac- 

 quainted with the mathematical theory. 



The following experiments were made with a detached pen- 

 dulum, both in vacuo and in air; a simple rod, with a knife- 

 edge, being used ; the clock pendulum was always adjusted to 

 the detached pendulum for the different extents of vibration, 

 and the rate of the clock was taken from another. In con- 

 ducting the experiments in air, the pendulum was not removed, 

 the air being merely readmitted into the vessel. 



Set, No. 1. — With a brass bob, 5 inches long and 4 inches 

 broad, of such a shape that a vertical section is rectangular, 

 and a horizontal section oval. 



ir.r~~f.~~.*. Gain in Extent of 



Experiments. ^ ^^ Vibration. 



In air + 3 ra 35*7 S 1*0° 



In exhaustion, 1 inch +3 44*0 1*0 



In air +3 34*0 1-5 



In exhaustion, 1 inch +3 40*8 1*5 



In air +3 30*5 2*0 



In exhaustion, I inch +3 37*5 2*0 



In air +3 26'3 2\5 



In exhaustion, 1 inch +3 33*0 2*5 



Set, No. 2. — With a cylindrical brass bob of 5 pounds 

 weight. 



t, . Gain in Extent of 



Experiments. ^ ^ Vibration. 



In air +3 m 11*5 S 1*3° 



In exhaustion, 1 inch +3 24*7 1*3 



In air +3 6*0 2*0 



In exhaustion, 1 inch +3 17*8 2*0 



Set, No. 3. — With an oval leaden bob of 10^ pounds weight. 



v . . Loss in Extent of 



Experiments. ^ ^^ Vibration. 



In air — l m 55'6 3 2° 



In exhaustion, 1 inch —1 49*5 2 



There being but a small difference between the results of 

 the experiments in air and in exhaustion, with the brass bob 

 of 5 pounds, and the results of those with the leaden bob 

 of 10*5 pounds, I was led to suspect that the surface of the 

 lead might have carried more air along with it than that of 

 the brass, and thus have caused a greater current. I there- 

 fore varnished the leaden bob, and the results of experiments 

 with it were as follows : — 



