schaller: calculation of mineral formulas 



97 



then placed in series with the inductance giving the larger deflec- 

 tion and adjusted until its deflection is reduced to that of the other 

 inductance. The resistance of the standard coil for the given 

 frequency being known, the corresponding resistance of the vari- 

 able inductance at this point is at once deterixiined. When the 

 variable inductance has been calibrated in this way for several 

 points and at various wave lengths, it at once becomes a standard 

 of comparison of resistance for any other inductances within its 

 limits, by a method similar to the above. If the values of the 

 resistances in Table II for any given wave length be plotted, it 

 will be found that the results do not fall on a straight line, that is, 

 the high frequency resistance increases more rapidly than in pro- 

 portion to the number of turns of the coil. This result is not in 

 accordance, I believe, with any of the various formulae which 

 have been given for the high frequency resistance of inductances. 

 The curvature appeals, however, only in the first part of the 

 curve. This is probably due to the distribution of the magnetic 

 field. 



IVIINERALOGY. — The calculation of mineral formulas. Walde- 

 MAR T, Schaller, Geological Survey. 



In the calculation of the ratios of a mineral analysis, it is cus- 

 tomary to select arbitrarily one of the constituents as unity, or 

 as some rational multiple of unity, and on this basis to calculate 

 the ratios of the other constituents. As an example I will give 

 the analysis of pearceite from the Veta Rica Mine, Sierra IMojada, 

 Coahuila, Mexico, as recently published^ by Frank R. Van Horn 

 and C. W. Cook. 



* Considered as (Ago) and (Cuo) respectively. 

 1 Amer. Journ. Sci. (4), vol. 31, p. 518, 1911. 



