from a Cylindrical Wall. 365 



In order to eliminate the heat radiated from the sur- 

 roundings, a guard-ring filled with crushed ice was used. 

 This was made so that the plate could be completely cut off 

 from exposure to the cylinder, and by means of an aperture, 

 equal in size to that of the plate, it could be exposed to the 

 cylinder at will. 



Observations were taken at half-minute intervals, a few 

 minutes with the plate covered, then exposed, and finally 

 with the plate covered again. The mean of the first and 

 last set of values was subtracted from the mean of the 

 second set and thus the heat radiated from the cylinder was 

 obtained. 



In the experiments, which were conducted with two 

 cylinders of different heights, the diameter of the plate was 

 practically equal to that of the cylinder, thus putting in the 

 expression (5) a = b, it simplifies to : 



11 



= a (IV - T 2 4 ) \ { V** + ^ ~ * 2 } "• 



c.c. 



This expression was used in the calculation : 



Average radius of plate and cylinder = 2'35 cm. 



Volume of capillary per cm. length =r •0201 



Mean contraction per minute when plate was 



covered = C] cm. 



Mean contraction per minute when plate was 



exposed = c 2 cm. 



IV %*• x i- - l V c i- c 2- o--c.,. irXlO 5 . 



373° ubs. '273° abs. 1*1 cm. 23 '3 cm. 2-3 cm. 2'88cm. -58 cm. 4*88 



l"5 „ 21-8 „ 1-26,, 1-76 „ -5 „ 4-88 



2'1 „ 24-3 „ -73., 112 ., 39 „ 4"94 



The accepted value of o-=5*32 x 10" 5 ergs, cm. 2 sec. de< 



In conclusion. I must express my great indebtedness to 

 Dr. (t. W. Todd, who suggested the problem and whose 

 advice and criticism lias been invaluable in the experimental 

 work. 



Royal Grammar School, 



Newcastle-on-Tynej 



Sept. 1919. 



