122 PKOCEEDINGS OP THE AMERICAN ACADEMY 



Strength of 

 Field. 



.007 

 .023 



.070 

 .103 

 .121 

 .139 

 .157 

 .176 

 .202 

 .224 

 .246 37.0 



Curve 2, Figure 1, represents the results when two of the ordinary- 

 ferrotype diaphragms were superposed, forming a diaphragm of double 

 thickness, and Curve 3 of the same figure shows the results when three 

 such diaphragms were superposed. Each diaphragm was 0.01 of an 

 inch thick. The curves of Figure 2, marked 21, 22, 23, respectively, 

 show the results of similar experiments with diaj^hragms of sheet iron 

 whose thickness was 0.030, 0.027, 0.024 of an inch, respectively (Nos. 

 21, 22, 23, B. W. G.). Figure 3 shows the results when a steel dia- 

 phragm 0.017 of an inch thick (No. 26) was used, the curve U being 

 that for untempered steel, and T that for tempered steel. Steel dia- 

 phragms respectively 0.026 and 0.012 of an inch thick (Nos. 22 

 and 30) gave similar results, as will be seen from Tables XI., XII., 

 and XIIL 



