282 Lord^Rayleigh on an Optical Device for the 



In converting hysteresis losses from one maximum induc- 

 tion-density B to another by the aid of Steinmetz's law, it is 

 useful to have the arithmetic values, for different values of B, 

 of the ratios of B 16 to 2500 16 ; since B = 2500 C.G.S. units is 

 generally taken as the standard induction-density in reference 

 to hysteresis determinations. The following table (Table IX.) 

 gives these ratios with sufficient accuracy for all practical 

 work. Thus, for instance, if the value of the hysteresis loss 

 in an iron has been determined at a maximum induction- 

 density during the cycle of 5000 units, and we wish to know 

 the value at 2500 units, the observed value has to be divided 

 by 3*031 to obtain the required result. 



Table IX. 

 Showing the Values of the Ratio of B 16 to 2500 1 ' 6 . 



B. 



B l-6 



B. 



B l-6 





2500 1 ' 6 





2500 1 " 6 



1000 



•231 



5500 



3-531 



1500 



•442 



6000' 



4-058 



2000 



•700 



6500 



4-614 



2500 



1-000 



7000 



5-193 



3000 



1-338 



7500 



5795 



3500 



1-713 



8000 



6-430 



4000 



2-118 



8500 



7-085 



4500 



2-563 



9000 



7-764 



5000 



3-031 



9500 



8-466 







10000 



9-190 . 



XXXVI. On an Optical Device for the Intensification of 

 Photographic Pictures. By Lord Rayleigh, F.R.S* 



WHETHER from insufficient exposure or from other 

 causes, it not unfrequently happens that a photo- 

 graphic negative is deficient in density, the ratio of light- 

 transmissions for the transparent and opaque parts being too 

 low for effective contrast. In many cases an adequate 



* Communicated bv the Author. 



