Natural Philosophy. — Magnetism. 4S5 
MAGNETISM. 
IS. Dr Wollaston! s Kocplanation of the Electro-Magnetic 
Phenomena. — In the Journal of Science, No. XX., Dr Wollas- 
ton is stated to have explained the phenomena of the conjunc- 
tive wire, (See this volume of our Journal, p.407.) upon the sup- 
position of an electro-magnetic current passing round the axis 
of the conjunctive wire, its direction depending upon that of the 
electric current, or upon the poles of the battery with which it is 
connected. This explanation will be understood from Plate VI. 
Fig. 5., No, 1. and No. S. In No. 1. the current is represented 
in two sections, at right angles to the axis of the wires when si- 
milarly electrified, from which it appears that the north and 
south powers meeting, will attract eitch other. In No. 2., the 
sections of the wire are shewn dissimilarly electrified, by which 
similar magnetic powers meet, and consequently repel each 
other. 
18. Ampere’’ s Electro-Magnetic Telegraph. — In the curious 
memoir of M. Ampere, of which we have already given a full 
account, he proposes to construct a Telegraph, by using as many 
conducting wires and magnetic needles as there are letters. By 
placing each letter on a different needle, he establishes, by means 
of the pile placed far from the needles, an alternate communica- 
tion betwixt its two extremities and those of each conductor, and 
thus forms a sort of telegraph, fitted for writing all the details 
which one may wish to transmit through any obstacle, to a per- 
son who is charged with observing the letters placed on the 
needles. By placing on the pile a row of stops, which would 
carry the same letters, and establish the communication by their 
descent, this method of correspondence might be made both easy 
and rapid. 
14, Cause of the Diurnal Variation of the Needle. — In the me- 
moir of M. Ampere above alluded to, he ascribes the Diurnal Va- 
riation of the Needle to the alternate change of temperature of the 
two regions, during the diurnal rotation of the globe, the influence 
of temperature on electric actions having been established by M. 
Dessaignes and others. We must also add,” says he, among the 
electro-motive actions of the different parts of the earth, that of 
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