180 



Transactions. — Miscellaneous. 



tinfoil was pasted on to the tubes. In the case of the other 

 metals used — lead, zinc, silver, and copper — the junction was 

 made by soldering. The only other metal that could be 

 obtained in thin sheets was aluminium, and the difficulty in 

 making a junction precluded its use. Unfortunately, only one 

 thickness of each of the metals could be obtained, and that 

 was so gi'eat that only one layer could be used 



The thickness of the metals somewhat restricted the scope 

 of these experiments, and rendered the method less sensitive 

 than it would otherwise have been ; while, in order to get 

 sufficient reduction of deflection with the needle placed in 

 direction h, it was necessary to use as a condenser four leyden- 

 jars arranged in parallel. The thicknesses of the metals used 

 were — 



Copper... ... ... 0-0134 millimetres. 



Silver ... .. ... 0-0108 



Zinc ... ... ... 0-0430 



Lead ... ... ... 0-0957 



Tinfoil ... ... ... 0-0116 



In the first set of experiments the condenser consisted of 

 two ley den- jars arranged in parallel. The length of the 

 needle used was 60-4mm., and it was placed in direction a; 

 for with the needle placed in direction h the copper, zinc, and 

 silver were thick enough to screen off all effect, while in the 

 case of the lead the screening was at least 95 per cent. The 

 observations made are here tabulated : — 



Metal. 



Original 

 Deflection. 



Reduced 

 Deflection. 



Silver 

 Copper 

 Zinc 

 Lead 



201 

 201 

 201 

 201 



141 

 144^ 

 1434 

 133 



Reduction. 



60 



57i 

 68 



The results obtained from these observations were that the 

 silver produced the same screening as 8 layers of tinfoil ; 

 that the copper was equivalent to 9-2 layers, the zinc to 8-8 

 layers, and the lead to 5-8 layers. 



