132 Mr. 8S. Tolver Preston on some Electromagnetic 
which emanate from the sun are supposed to revolve with the 
sun. The magnet may even, in certain cases, be considered 
as revolving amongst its own forces, and producing a full 
electric effect sensible at the galvanometer.”’ (Phil. Trans. 
1352, page 31.) 
Without at once going into the related practical question 
as to whether a magnet (the rotating globe of the earth, for 
instance) can, by “ revolving amongst its own forces,” become 
charged at the equator and poles with electricity of opposite 
sign (as Faraday * inferred from this experiment), I would 
only wish to call the unbiassed attention to the above distinction 
im principle between a translatory and a rotatory motion, as it 
seems to me that such a distinction (as a matter of theoretic 
reasoning) cannot possibly hold. For rotation is surely after 
all only a particular case of translation, viz. translation in a 
circle. When a magnet rotates on its axis, every part or 
magnetic point in it 1s translated (in a circle) about that axis. 
And certainly it will be conceded in regard to Faraday’s 
analogy of the (axially) revolving or rotating sun, the same 
principle (whatever it was) that applied to the behaviour of 
the “rays of light” of the rotating sun, also must apply to 
the rays of light of the translated sun (in its proper motion). 
For we do not ask whether a given luminous point or portion 
of the sun’s surface is moving in a curved or in a straight line 
in order to set fast the principle of the behaviour of the rays of 
light. The same reasoning must therefore apply to the magnet 
if Faraday’s analogy is to hold at all, z.e. if (in regard to the 
inductive effect) the lines of force must be regarded as par- 
taking of the motion of a magnet when it is translated, they 
must partake of its motion when it is rotated t. ‘This, there- 
fore, constitutes the first theoretic objection to the view adopted 
by Faraday, and it seems to me to be in itself conclusive. 
But, for the sake of further illustration, I will point out how 
this view clashes with the generally accepted similarity in (at 
least) fundamental properties between the solenoid, or helix, 
and the magnet. 
It seems always to have been taken for granted that when 
a solenoid, or a simple circular current, rotates on its axis in 
* Plticker also inferred it from an analogous experiment, and remarks, 
“‘ Hier tritt alsdann in den beiden Polen die positive, unter dem Aequator 
die negative Elektricitat auf, wahrend eine Indifferenzzone zwischen dem 
Aequator und jedem der beiden Pole liegt.” (Pogg. Ann. 1852, p. 357.) 
+ Or, in other words, if the lines of force emitted by a given portion of 
a magnetic surface must be considered as partaking of the motion of that 
portion of surface, when it is translated in a straight line, they must equally 
do so when that portion of surface is translated im a curved hne (by the 
rotation of the magnet on its axis). 
