1866.] 



Electricity given by Induction- Machines. 



179 



1 . As before, two helices in series give no increase of quantity ; M + N 

 is the same as N, G + L nearly the mean of G and L. 



2. The quantity of collateral hehces is seen in column 6 (as in Table II.) 

 to be the sum of the separate actions of each. The discrepancies are not 

 greater than what can be explained by the uncertainties inherent in these 

 measures, which I have already described. One apparent exception is a 

 strong confirmation of this rule — the case of G . H (1 + K). Its observed 

 $=3"0552, while the sum =4'6220. G and I being on the same primary 

 are excited together ; but in measuring either, as there is no current in the 

 other (but merely a state of tension), their n is not changed. When, 

 however, they are connected collaterally, the currents react on each other, 

 their El's are increased : the ^>'s are thus diminished, and therefore their 

 resultant is the sum of quantities less than those used in the computation. 

 The 6's in this case become— for G 0-94289, for H 07988o, and for 1 + K 

 0*34588, which are quite sufficient to account for the difference. 



3. As with I in Table II., so here it will be observed that N has less 

 relative power than either I or K ; its actual power is even less, though its 

 theoretical force exceeds theirs in the proportion of 5 : 4. This is explained 

 by its b being so much smaller ; but it gives this important information, 

 that, at least in helices of these dimensions, nothing is gained by using wire 

 thicker than that of I, or of an inch*. 



4. The effect of L is far less than that of I-f- K. In the first the helices 

 are on the same primary, in the other on separate ones. In the former 

 case the II is larger, for it is the sum of the n of each on itself, and those 

 of each on the other ; b therefore is less. Besides, the potential of the 

 core on the helices is less than when each of them is central on it. 



The difference is even more remarkable in O as compared to its elements 

 M-j-N, its effect being only 0*7 of the other, and 0*3 of the theoretic 

 power. The same disparity of course prevails in their combinations ; O . L 

 giving only 3*46, while the same four helices arranged on separate prima- 

 ries give 8-19. The combinations G , H (I + K) and G . L . H have the same 

 helices ; but in the first two were on the same primaries. As, however, 

 they were 1*5 inch instead of 0*5 apart, the 11 was not so much increased 

 as in the other cases, and therefore there is not quite so great a decrease 

 of power. 



The following practical maxims may be deduced from the experiments 

 and reasoning which I have related. 



The attention of instrument-makers has been chiefly directed towards 

 increasing the length of spark given by these machines, and in this they 

 have succeeded to a surprising degree ; but in doing so they have not 

 added to the quantity of electricity which is produced by them. This, 

 however, is by far the most important object ; for in most applications of 



* This is between 27 and 28 of the Birmingham wire-gauge. I believe Euhmkorff 

 uses 28. 



VOL. XV. a 



