IN MAGNETISM AND ELECTRICITY. 
97 
evolved, varied with the length or the resistance of the wires which joined the poles of 
the machine. It therefore became necessary to change the position of the commutator 
on the armature axis, to suit the different circuits through which the electricity was 
transmitted, so that the burning effects of the spark at the junction of the two halves of 
the commutator might be avoided when the direction of the current was changed. 
37. When the commutator was properly adjusted to the resistance of the wires sur- 
rounding the electro-magnet (33), I observed that so long as the magneto-electric machine 
was allowed to run without its poles being connected, either with the wires of the electro- 
magnet or any other conductor, a brilliant star of light appeared at the points where the 
springs were in contact with the commutator (15) ; but when the poles of the machine 
were connected by means of a short piece of wire, the bright light at the commutator 
instantly disappeared. It was also observed that when the poles of the machine were 
connected with the long helices of the large electro-magnet, a perceptible interval of 
time elapsed before the light at the commutator disappeared. Besides this, it was also 
observed that, at the moment of breaking contact between the wires of the electro- 
magnet and the poles of the machine, a much more brilliant spark appeared at the 
points of separation, and a much more severe shock was felt Avhen the body formed part 
of the circuit, than could be produced by the direct action of the machine alone. The 
latter effects could not, however, be obtained until a certain interval of time had elapsed 
after contact had been made between the electro-helices and the wires of the machine. 
38. Moreover, I found that a spark could be obtained from the wires surrounding the 
electro-magnet even after they had been entirely disconnected from the machine. This 
curious result was obtained by first holding the free extremities of the wires surrounding 
the electro-magnet, one in each hand, in contact for a few seconds with the respective 
polar terminals of the machine, and while contact was still maintained, bringing the 
ends of the electro-helices into metallic contact with each other, so that they formed 
a continuous metallic loop or closed circuit. The loop so formed Avas then suddenly 
removed from the polar terminals, and while thus entirely disconnected from them, the 
ends of the loop were suddenly separated, and a bright spark appeared at the point of 
disjunction. With a larger and more powerful electro-magnet (67, 68), a bright spark 
Was in like manner obtained, twenty-five seconds after all connexion Avith the magneto- 
electric machine had been broken *. 
39. None of the effects described, such as the great sustaining-poAver of the electro- 
magnet above that of the permanent magnets (34), the increased brilliancy of the spark 
at the point of disjunction of the Avires (37), or the spark from the electro-helices after 
all connexion Avith the magneto-electric machine had been broken (38), Avere observed 
Avhen the alternating current from the machine (16) Avas transmitted through the electro- 
helices, instead of the direct current from the commutator (15). Under these conditions 
* Since this paper Avas read I have discovered that Dr. Page, in 1851, succeeded in obtaining a spark from 
an electro -magnet, coiled with a very long Avire, half a second after all connexion with the battery had been 
broken. — Sillimax’s American Journal of Science, vol. xi. p. 88. 
MDCCCLXVII. 
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