464 Prof. R. Threlfall on the Measurement 



Magnet B. 



Position in Toil Double displacement with Number of 



current + and — . experiments. 



At edge of coil . . . -43 centirn. 3 



i way in -77 „ 2 



* „ 1-03 „ 2 



I „ 1*159 „ 2 



Near bottom of coil . . 1*04 „ 2 

 (-J- inch off) 



?? 



Magnet B reversed, otherwise everything the same. 



p • , . Displacement current Number of 



+ and — . experiments 



At edge . . , . . . . '415 centim. 2 



i way in ...... -78 „ 2 



i ), ...... 1-085 „ 2 



I „ 1-27 „ 2 



i off bottom Ml ;, 2 



The nett result was that all the magnets behaved best when 

 they started from three quarters to the whole way in, and 

 that B was best, C almost as good as B, and A distinctly the 

 worst. On reducing the observations it turned out that the 

 ratio of the mean displacements of A and B was about *782, 

 while the ratios of the magnetic moments was *755. This 

 relation is of about the order one would expect, seeing that 

 the length of the magnets was about 9*6 centim. and the 

 dimensions of the coil were : — axial 3*8 centim., radial at one 

 end 2*4, radial at other end 2*5. The external surfaces of 

 the coils were cylindrical. 



The ratio of the greatest displacements was *643. It may 

 be conceded, therefore, that the questions of magnetization 

 and placing received a fairly complete answer. In the final 

 arrangement of the galvanometer with horseshoe magnets, 

 like those described by the Messrs. Gray, the lengths of the 

 yokes of the magnets was 8"5 centim., and thus this was the 

 distance between the centres of the coils. The legs of the 

 magnets were 3*8 centim. long, and they were magnetized 

 like the trial magnet B. When in position, the magnet-legs 

 projected into the coils to an extent of about j the axial 

 dimension of the latter. The suspension was two washed silk 

 fibres (one would not carry the load) 16 centim. long. 



The test for sensitiveness was made by running a large 

 Clark cell (already described) through 10,000 legal ohms, and 

 a certain small resistance taken out of an ordinary Bridge-box. 

 The terminals of the Bridge- box were coupled up through the 



