1 6 Prof. Buff on the Conductivity of Heated Glass for Electiiciiy, 



to 2°. When greater differences exhibited themselves, the expe- 

 riments wherein they were exhibited were rejected. 



It was further ascertained by a particular series of experiments, 

 that the first impulsions, as long as they did not exceed 40°, 

 through multiplication by the factor 0*74, gave the corresponding 

 permanent deflection with sufficient accuracy. 



By means of the deflections ascertained in this manner, and 

 the equations derived from the law of Ohm, 



rtan79°=K and (L + r) tan/9=sK, 



the resistance of the glass at different temperatures has been cal- 

 culated. L denotes here the resistance sought, r the known 

 resistance of the multiplying helix, which is so considerable that 

 the resistance of a single pair of Daniell, or even several of them, 

 disappears in comparison ; /S is the permanent deflection of the 

 needle, K the force of an element of Daniell. From these equa- 

 tions we obtain 



T tan 79°- tan ^ 

 tan/S 



The observations, and the resistances deduced from them, are 

 contained in the following table : — 



livy 



The numbers in the last column show the ratio in which the 

 resistance diminishes. If these numbers be chosen for ordinates, 

 the temperatures, increasing in arithmetical progression, being 

 chosen as abscissae, we find that the curve thus foraied falls 

 very steeply at the commencement, and then approaches the 

 abscissa asymptotically. From the numbers stated in the fore- 

 going table the following one has been calculated by intei7)o- 

 lation, in which, of course, the values which lie beyond the 

 limits of observations can only be a probable approximation to 

 the truth. 



