516 



The Rev. T. R, Robinson's Experimental Researches on the 



giving the greatest number possible of spires, and the shortest magnet. The 

 observed values of L are reduced to 60' by the coefficients of (12). 



Table VIII. 



As higher values could not easily be obtained without some risk of destroy- 

 m" the spirals by the evolved heat, I use, when necessary, the numbers of Table 

 XII. obtained with the helices B, whose ratio to A is known. 



II. We can now compare spirals of different diameters, and thus ascertain 

 how far the preceding theory agrees with experiments. The cylinders were 

 set to 0'-6, which permits the use of spirals 7'-.5 diameter by overlapping 

 them. The spirals are made of flatted copper wire 0-2 by 0-05, to enable the 

 employment of powerful currents with such batteries as I possess;* but 

 experience makes me regret this arrangement, for it requires a greater length 

 of cylinder, and the action of the current is probably not quite uniform 



* The current employed with (C) would evolve in a voltameter 18 cubic inches of mixed gases 

 l)er minute. 



