^«**^^ Iv of the Induction Coil, ,(' ?M 383 



duced a maximum temperature of 35 degrees, but the sparks 

 between the terminals were much longer, averaging about 0-4 of 

 an inch. The temperature fell a few degrees on pushing the 

 striking distance to its greatest extent, but was pretty constant 

 at all distances between the extreme length and the shorter in- 

 terval, about 0*1, at which the negative point became ignited. 



17. A jar of half a square foot, of rather stouter glass, about 

 the same thickness as the large jar, gave a maximum temperature 

 of 15 degrees, and the maximum length of spark was 0*5 of an 

 inch ; but the negative terminal now became heated, when the 

 striking distance was reduced to 0*2 of an inch ; but between 

 these extremes the temperature indicated by the electrometer 

 was not influenced by any variation in the length of the sparks. 



18. On comparing the results of these jars with each other, 

 they appear to have produced effects bearing a direct relation to 

 the extent of their coated surfaces; for although the jar of 

 1 square foot gave an effect rather more than was due to its 

 relative surface, yet being thinner it was capable of holding rather 

 a stronger charge ; and without the least desire to coax results, the 

 simple relation of effects to causes appearshere strikingly manifest. 



19. In a subsequent series of experiments an extra unit of 

 measure, containing a quarter of a square foot, was added; and 

 here the effects were in relation to each other as 1, 2, 4+12, 

 corresponding to the relative extent of the surfaces of the jars, 

 the thin jar of 1 square foot (4 + ) still remaining the exception. 

 When however two jars of 3 square feet were connected as a bat- 

 tery, so as to double the surface of the last element, the resulting 

 temperature was only 115 degrees, and the spark between the 

 terminals much shorter. 



20. In each set of experiments care was taken to conduct the 

 whole as speedily as was consistent with accuracy, so as to obtain 

 the whole of the results before the action of the voltaic battery 

 began to subside ; and it was curious to remark, that as it gra- 

 dually lost power, so the largest jar gradually lost the relation- 

 ship which it originally bore to the others. 



:■■ 21. The results here detailed appear to indicate, that, with a 

 given surface, the heating effect of the electrical discharges does 

 not vary with the length of the spark within given limits, other 

 things remaining the same. 



J 22. That the heating effect of different surfaces appears to be 

 in the direct simple ratio of their respective areas, up to the 

 point at which the quantity of electricity transmitted by each 

 wave of the induced current is capable of developing the maxi- 

 mum effect of the coated surface in relation to its own tension. 



h 23. On varying these experiments by exciting the coil more 

 or less powerfully, the same relation between surface and heating 

 effect was observed whatever was the value of the unit indicated 



