RATIO OF ELECTROMAGNETIC TO ELECTROSTATIC UNIT 269 



LARGE COILS. 



Total number of windings 240 



Depth of groove -84 cm. 



Width of groove -76 cm. 



Mean radius of coils 13-741 cm. 



Mean distance apart of coils 13-786 cm. 



SUSPENDED COILS. 



Total numher of windings 126 



Depth of groove -41 cm. 



Width of groove -38 cm. 



Mean radius 2-760 cm. 



Mean distance apart 2-707 cm. 



These data give, by Maxwell's formulae, 



(7 = 0-006457. 



In order to be sure of this constant, I constructed a large tangent 

 galvanometer with a circle 80 cm. diameter and the earth's magnetism 

 was determined many times by passing the current from the electro- 

 dynamometer through this instrument and also by means of the ordi- 

 nary method with magnets. In this way the following values were 

 found. 



Magnetic Electrical 



method. method. 



December 16, 1879 -19921 -19934 



January 3, 1879 -19940 -19942 



February 25, 1879 -19887 -19948 



February 28, 1879 -19903 -19910 



March 1, 1879 -19912 -19928 



Mean -19912 -19933 



which differ only about 1 in 1000 from each other. Hence we have 

 for C: 



From calculation from coils -006457 



From tangent galvanometer -006451 



Mean -006454 c. g. s. units. 



The suspension was bifilar and no correction was found necessary for 

 the torsion of the wire at the small angles used. 



