337 



doubt, it appeared to exist or give light much longer than it did, we 

 judging by our sensations only. 



The character of the short spark sometimes differed from that just 

 noticed, the colours extending only half way ; still the two colours con- 

 tinued the same, .and each held its peculiar character, the blue-white 

 light appearing to be compact and uniform, like the centre of a sheet of 

 perfect flame, while the salmon-colour appeared like the edge of the 

 flame of a lamp of impure hydrogen, having a character like hair or lu- 

 minous filaments, striking away in all directions into space, but of its 

 own peculiar colour. 



In some cases where the difference of colour of the halves of the 

 spark were most distinctly observable, as if they did not mix or overlap 

 each other, a knob or ball excrescence appeared in the centre of the 

 spark. Its core was always composed of the bluish and white light, 

 surrounded with the salmon-coloured. Here in the centre of the space 

 between the two points, the advocate of the doctrine of the two electric 

 fluids might tell us, they met and fought ; and that while the salmon- 

 coloured fluid devoured the blue and whitish fluid, the latter exploded, 

 totally destroying all appearance and trace of its enemy. 



When the sparks were long, we could notice a difi'erence in their co- 

 lour, and in intensity or quantity, no two sparks appearing to be exactly 

 alike, but I did not notice any knobs on those sparks ; yet I suspect that 

 there may have been such lumps at every joint, angle, or break, in the 

 continuity of the line which these long sparks made in their passage 

 through the air, though we did not notice them. 



In machine electricity it is generally said that sparks pass between 

 the nearest points, or shortest distances, but this statement is to be re- 

 ceived under correction; for sparks taken from prime conductors of 

 diff'erent shapes are themselves different to each other. And if a prime 

 conductor of an electrifying machine be very long, the sparks taken 

 from diflerent parts of it are found to strike at difl'erent distances ; 

 so that, though we may, in general terms, adopt the rule that machine 

 electric sparks prefer the shortest distances, yet the long sparks pro- 

 duced by the induction coil of Dr. Callan, in not one instance, that 

 I observed, adopted that law. On the contrary, they appeared to most 

 carefully avoid it, when taken between a point on the right hand and 

 the slightly hollowed tin disk on the other. 



According to the eye, the sparks started from the point, and struck 

 indiscriminately on every part of the disk; and some of them, more 

 wild or eccentric than the others, and as it were to set old-fashioned 

 theories at defiance, actually jumped over its edge, and turned about, 

 and struck the back of the disk,— thus imitating some well authenti- 

 cated freaks of real flashes of lightning, which have been seen to go be- 

 yond, and, as it were, turn about and strike objects which they had 

 apparently attempted to hit, but failing, turned round, and thus accom- 

 plished their original purpose in this most extraordinary or unscientific 

 manner, as an old electrician might say. 



