W. P. Ileadden — Golumbite and Tanialite. 89 



I have used simply an orthogonal projection as the easiest to 

 illustrate the theory, but obviously the vanishing point may be 

 placed at A, and the necessary modification introduced into the 

 formulae. It may be remarked that since the visible distance 

 of an aurora can be estimated within narrow limits, as it must 

 be closely related to the latitude of the station, it will not be 

 difficult to make the first assumption of the angle within easy 

 range for computing. The change in the value of v is really 

 a variation of the distance of the ray from the observer, and 

 it is this quantity that has been so difficult to secure. Having 

 once derived this distance correctly, a whole series of problems 

 lie ready for discussion, as arising in meteorology and terres- 

 trial magnetism. 



1 have shown in a recent paper that the coronal action of the 

 sun arises from a potential of the magnetic type, and from 

 magnetic observations it has been found that this influence is 

 felt at the distance of the earth from the sun, as indicated by 

 the responsive display of auroras after some outburst of the 

 solar energy. It is to be hoped that this disturbance may be 

 traced in the auroral lines, by their inductive displacement in 

 the upper regions, though it may be too small a quantity to be 

 detected by the observations. The whole subject of cosmical 

 interaction of the sun and the earth, through the medium of 

 the ether is so important, that this question of the aurora is 

 one of vital significance, from its connection with it. I there- 

 fore venture to appeal to observers to make such observations 

 of the auroral rays as I have indicated. My only apology for 

 presenting the theory without experimental evidence is the 

 fact that these measurements do not exist, although there is no 

 reason to suppose they will be very difficult to make, and they 

 will undoubtedly be interesting in future discussions of the 

 subject: 



Art. XII. — Columbite and Tantalite from the Black Rills 

 of South Dakota ; by W. P. Headdek* 



1. Columbite. 



The occurrence of columbite in the Black Hills was first 

 noticed by Prof. W. P. Blake in 1884. t The localities then 

 known were the Etta and Bob Ingersoll mines, in Pennington 

 Co., S. D., and within a few miles of each other. Since that 

 time the mineral has been found at a number of localities in 



* The larger part of this article was read before the Colorado Scientific Society, 

 Aug. 4th, 1890. 



f This Journal, xxviii, 340, 1884. 



