1894] Presents. 43 



Now throw away the operand NvscH, and we get the velocity 

 equation pure and simple, and the index equation (3) then comes by 

 s = Ntr 1 . 



But, although the above manipulation of the characteristic equa- 

 tion has some analytical interest, the process cannot be always re- 

 commended on the score of simplicity. It is, on the contrary, usually 

 easier and simpler to work upon the component equations upon which 

 the characteristic is founded. 



Presents, January 18, 1894. 

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