458 Intelligence and Miscellaneous Articles. 



is the number of turns, and the magnetizing power M of the coil is 



M=SW=- if ™. (4) 



X . m m 



If, again, <r is the specific gravity of the copper, and G the absolute 

 weight in grammes of the wire used, then 



G= rfW . (5) 



and therefore 



se 



X m m 



M *7 3 s 



a/g 



fmd\ 



(6) 



The expression is constant so long as the number, the electromo- 

 tive force, and the internal resistance of the cells, as well as the 

 width of the coils and the specific gravity of the wire, remain the 

 same. 



For . , m X 



n=st, and — =s-> 

 er t 



from which there is easily obtained 



fnXd 2 , ft 



= \ / > and 5= a / - 



alues in equation (6), ai 



mn 



By substituting these values in equation (6), and simplification, we 

 have M _ e f~2n 



an expression which is quite independent of the thickness of the wire 

 and the mode of combination of the battery, and which is constant 

 as long as the width of the turns, the number, electromotive force, 

 and internal resistance of the cells, and the specific gravity of the 

 wire are unchanged. 



Hence generally, the circumstances remaining constant, the mag- 

 netizing powers of coils of one and the same metal, with a maximum 

 intensity of the current in each case, are as the square roots of the 

 Weights of the wire used. — PoggendorfTs Annalen,November I860. 



ANOTHER NEW FORM OF THE HELIOTROPE. 

 BY K. A. STEINHEIL. 



The interesting paper of Professor Miller of Cambridge (Phil. 

 Mag. S. 4. vol. xxx. p. 71), on two new forms of the heliotrope, reminds 

 me of one which some thirty years ago I had made, and which since 

 then has been kept in the physical collection of our State, but has 

 never been described. A knowledge of it may contribute to complete 

 the literature on this subject. 



In determining heights by triangulation, it is desirable, in order 

 to get rid of part of the uncertainty of the path of a luminous ray 



