314 Messrs. Stewart and Tait on the Heating of a [May 15, 



It will be seen by art. 39 that the residual effect obtained from a disk 

 covered with chamois leather is approximately the same as that from an 

 uncovered disk ; this would appear to us to be against the vibration hy- 

 pothesis. 



In the following experiment the disk was covered with a chamois- 

 leather blind with a segment cut out as underneath — 



A mean of two sets of experiments (consisting of 16 separate observa- 

 tions, and embracing results immediately after rotation, as well as results 

 one minute after) gave as the result of tapping in A with dry hydro- 

 gen 47, while a mean of 24 similar observations with the same atmosphere 

 gave as the result of tapping an uncovered disk 53. Allowing for errors 

 of experiment, we may conclude that this arrangement does not much in- 

 fluence the results. 



41. The disk was next treated in the following manner : — 



It][was covered with a chamois leather blind tied into holes drilled in 

 the disk, and having the above shape. The mean of 3 sets of experi- 

 ments similar to those in art. 40 3 and consisting of 18 separate observa- 

 tions, gave as follows for an atmosphere of ~ 3 y- dry hydrogen, tapping in 

 A 54, tapping in B 56, which two results are approximately equal to one 

 another, the mean being 55. 



The mean of 3 sets of experiments, consisting of 24 separate observa- 

 tions for an atmosphere of hydrogen, but with an uncovered disk, gave 

 53 as the heat-result. All these experiments apparently combine to 

 prove that the result is not due to vibration. 



42. When the atmosphere was ^ hyd.-f -^ - air, we also found A and 

 B approximately the same, A giving 181 while B gave 182 • we have 

 therefore not hesitated to combine together the results of tapping in this 

 atmosphere, whether at A, or at B, or with an uncovered disk, in the 

 comparison given in art. 38. 



