268 
POPULAR SC1E>XE REYIEAY. 
it may appear somewhat strange when we say that many months 
elapsed before that gentleman could get a competent firm to 
carry out his patent. People will sometimes he slow in yielding 
assent to anytliing that clashes with their natural conservatism. 
Franklin himself was made the object of some harmless plea- 
santry on* account of his ideas about lightning-rods by one of 
the most distinguished bodies in. Europe, our own Eoyal Society. 
But M. Werdermann ultimately found a firm able and whiling 
to undertake the construction of his machines. Public interest 
was soon awakened by the results obtained by l\Ir. Conrad W. 
Cooke, in presence of some of the leading scientific men of the 
day and the representatives of the press. We had the privilege 
of examining the apparatus at our leisure, and of witnessing on 
three consecutive evenings a series of experiments, of which we 
shall speak after w^e have briefly discussed the technical parts of 
the apparatus. 
It is necessary to premise that the construction of the 
machine depends upon the uses to which it is to be applied. If 
required for electro-chemistry, it must give quantitative effects ; 
and if for illumination, tensional. As a general rule, these may 
be attained by varying the length and gauge of the wire and the 
connection of the bobbins ; but besides these, other changes are 
introduced into this machine, which accordingly modify its 
appearance. The one showui in perspective on the accompany- 
ing plate (Plate Cl. fig. 1) belongs to the second class. It 
consists essentially of several bobbins or armatures rotating 
before the poles of tw^o rows of cylindrical electro-magnets. 
These occupy a vertical position, with similar poles opposite, 
but not in contact with, each other. They are 3 ft. inches 
high, and 3^^^ inches in diameter. The height of the machine 
is 4 ft. l-j3^ inches, and its weight one ton. The armatures 
form quite a novel feature in magneto-electricity, and the idea 
is entirely M. Grramme’s. It occurred to him that Siemen’s 
long cylinder might be replaced by a ring. Accordingly, he 
coiled insulated copper wire around this core, and imparted to 
the whole a movement of rotation in a plane perpendicular to 
that of the adjacent electro-magnets, when he obtained un- 
inter mittent currents with maximum effect. Let N and s (fig. 
3, Plate Cl.) represent the north and south poles of one of the 
magnets. They will induce consequent poles at ss and nn in 
the adjoining portions of the ring; h and c on the magnetic 
equator will be the neutral points. The movement of the 
coil before N will induce in the wires currents which are posi- 
tive in the upper quadrant, and negative in the lower Nc. 
Owing to the opposite polarity of s, a -f- current flows through 
s6, and a — through sc. As consecutive parts of the helices 
are constantly coming within the influence of N and s, it 
