178 



Rev. T. R. Robinson on increasing the [May 31, 



current is only 2-5. This is at once explained by its h being so mucb less. 

 So also the ratio of the theoretic to the effective current is nearly unity 

 in G + H, while it is only 0*73 in V+V, and for the same reason. In 

 G . H . (I + K) the ratio is still smaller ; but I shall recur to this. 



I now used the four primaries I + K=L on P'^ single helices on the 

 others. I had some doubt whether the difference of the cores might not 

 influence the results, and tried this with P', P'", and one P"", whose core 

 = 1*90 inch in diameter and 15*5 inches long. It has 349 spires of No. 15 

 in two layers. G was put on each of them, and currents transmitted, 

 which made their "^^'s nearly equal. 



Table III. 



Name. 



Sect, of 



core as 





Sets. 



Spark. 









I'OO 



i-o4i4"^'' 



3*5 



2*225 



1169 



piv 



2-04 



i-oooo 



2* 



3"237 



1168 







3"oo 



1*0054 



2* 



2*662 



115-6 



It follows from this that the least of these cores is large enough for the 

 excitation produced by four cells : the size does seem to increase the spark, 

 though this increase may be owing to better insulation of the core-wires in 

 F" and P^f. 



The following results were obtained with the mechanical rheotome worked 

 at a uniform speed of 13 discharges per second. 



Table IV. 



a 



L=I+K . 



G+L 



G-.L 



H 



C=A+B . 



N 



I 



K 



a.K 



G.L.H.... 

 G.L.C .... 

 G.L.C.H. 



M+N 



= 



S = M+N . 



L.O 



MNIK . 





F. 



Sets. 





Sum of 

 components. 



n. 



b. 



1*0000 



I'OOOO 





1*00000 





1*00000 



i"oo779 



1-8832 



4*5106 



19 



0*41752 





0*6+ 



0*34624— 



1*3149 



1-6143 



2 



0*81451 





1*6+ 



0-75002 — 



3*0402 



5*3109 



11 



0-57159 



2*8324 







1*4196 



1*3578 



2 



1*04551 





I'OOOOO 



0*85385 



1-9882 



2*OII2 



2 



0*99855 





0*562864- 



0*92704 



2*5535 



5*4100 





0*47202 





0*31646 



0-27756 



2*5580 



4*3635 



2 



0*58623 





0-23149 



0*46542 



2*6465 



4*3635 



5 



0-60651 





0-23149 



0*46542 



3*5558 



5*2464 



1 



0*67776 



3*8594 







4*3179 



6-5756 



3 



0*65666 



4*1799 







5*1460 



6*9400 



3 



0*74153 



4-6932 







6*0758 



8*2081 



3 



0*74030 



6*0488 







2*5207 



5*4586 



2 



0*46179 





0*63292 



0-26862 



1*7616 



5*4586 



4 



0*32271 





0*73130 



0*23248 



1*6687 



4-9644 



1 



0*33614 





0*65810 



0*28543 



3*4596 



9*5774 



I 



0*36124 



3-4996 







8-1939 



15*7398 



I 



0*52058 



8-2736 







* 2-5 sets taken on the first day were very unsteady. The one taken on the second 

 was' close, and gave 1-0267. 



f At the same time I tried two hehces similar to A and B, except that their wire is 

 varnished iron, which were given to me by Dr. Callan. Their $ is 0-6887, and their 

 spark only 0-524 in. The $ of A + B is 2-9138 times as great, a difference caused 

 solely by the greater resistance of the iron. 



