188 DB. EVEEETT ON THE EIGIDITY OF GLASS. 



•0423 effect per gramme. 



The mean of -0427, -0423, -0423 is -04243, which is adopted as the mean effect per 

 gramme in this position of the rod. 



1 may here state that, from a careful analysis of several observations, both of torsion 

 and flexure, I have come to the conclusion that the mean separation of images pro- 

 duced by weights of 100 grammes is, vnthiu the limits of accuracy attainable in these 

 experiments, precisely double of that produced by weights of 50 grammes. In several 

 sets of observations the deviation from strict proportionality amounted only to about 

 1 part in 500, and this deviation was sometimes on one side and sometimes on the 

 other. 



When the experiments above described were concluded, the ends of the glass rod were 

 cut off just outside the clamps, and the remaining portion was weighed in air and water. 

 The weights were respectively 40-317 and 26-620 grammes, showing a loss ia water of 

 13-697 grammes ; and siace a gramme is the weight of a cubic centimetre of water, this 

 last number expresses the volume of the rod in centimetres. The length was found to 

 be 28-2; hence the mean sectional area is -48571, and the mean radius -39321. No 

 correction is applied for the temperature of the water (2° Cent.), as its amount would 

 be only about 1 part in 5000. 



