BULLETIN 



PHILOSOPHICAL SOCIETY OF WASHINGTON. 



185th Meeting. October 9, 1880. 



The President in the Chair. 



The minutes of the last meeting were read and adopted. 



The President notified the meeting of the decease of Prof. Peirce' 

 whereupon 



Mr. Elliott moved the appointment of a committee of three, to 

 be appointed by the Chair, to draft resolutions in accordance with 

 the notice just given and submit the same at the next meeting. 



The Chair appointed as Committee : J. E. Hilgard, J. H. C. 

 Coffin, and Wm. Ferrell. 



The treasurer notified the meeting that Vol. 3 of the Bulletin 

 had been published, and that a copy would be forwarded to all 

 members not in arrears. 



Mr. C. Abbe communicated the first part of a paper on the 

 Aurora Borealis, referring to studies made by him on the appear- 

 ance of the aurora of April 4, 1874. He spoke of the difficulty 

 which beset the consideration of the explanation of the appearance 

 of the aurora, and especially of obtaining the altitude of the arch. 

 The present modes of measuring the height yield only negative 

 results, as shown by the experiments of Bravais and Martin, using 

 the trigonometrical method. The second mode employs the varying 

 amount of dip at separate localities, using it according to Galles' 

 method, which assumes the dip of the needle to be of the same 

 amount in the upper regions of the air as at the earth's surface, 

 which has not been proved. Mr. Abbe also referred to Gauss' 

 formula for calculating the direction and intensity of magnetism for 

 all localities, and the defects in Galles' method of calculating the 



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