402 Efectiveness of a Magneto-Teleplwne as a Transmitter. 



Carve 2, fig. 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 O'Ol of an inch thick. 

 The curves of fig. 2, marked 21, 22, 23, respectively, show 

 the results of similar experiments with diaphragms of sheet 

 iron whose thickness was 0"030, 0"027, 0*024 of an inch, 

 respectively (Nos. 21, 22, 23, B.W.G.). Fig. 3 shows the 

 results when a steel diaphragm 0'017 of an inch thick (No. 26) 

 was used, the curve v being that for untempered steel, and 

 r that for tempered steel. Steel diaphragms 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 

 XIII. 



An inspection of these curves shows immediately that the 

 greater the strength of the field required to saturate the dia- 

 phragm, the greater is the strength of the field at which the 

 maximmn current occurs. Thus in fig. 1 the maximum cur- 

 rent with curve 1 corresponds to a strength of field of about 

 12 units of the scale used, while with curves 2 and 3 the 

 corresponding strengths of field are 20 and 43 units respect- 

 ively. Also in fig. 2 the maximum currents will be seen to 

 correspond to greater strengths of field in {)roportion to the 

 thickness of the diaphragm ; and in fig. 3 similar though less 

 marked results hold for tempered as compared with untem- 

 pered steel of the same thickness. 



It would also be exi)ected that the value of the maximum 

 current would be greater with a thick than with a thin dia- 

 phragm. This was usually the case in our experiments. 

 Thus the curves 1, 2, 3 of fig. 1 give maximum currents of 

 27-5, 50-2, and 62'6 units respectively. Eesults of a similar 

 nature are shown by fig. 3, the maximum current with the 

 untempered diaphragm being far greater than with the tem- 

 pered one. Curve No. 23 of fig. 2 is apparently an exception. 

 It is probable, however, that this is in appearance only, and 

 that the three curves of that figure are not strictly comparable 

 with one another. The rigidity of the diaphragms here used, 

 especially of the thicker ones, is considerable ; and any slight 

 yielding of the supports of the rod which carried the cam 

 would prevent the actual throw of the diaphragm from being 

 as great when this had considerable thickness, and would 

 greatly diminish the strength of the current produced. 



The peculiarity of curve 2, as compared with 1 and 3, is 

 probably caused by the want of both magnetic and mechanical 

 continuity in the material of the multiple plate formed by the 

 several diaphragms used. 



