38 Onan Equaiion in Laplace’s Mécanique Céleste.. 
that of the excited surface obtains in the leaves of Mr. 
Walker’s electrometer. The imperfect insulation of the 
instrumcnt, or the striking of the gold-leaves against the 
tinfoil on the sides of the glass, are the sources of uninsu- 
Jated contact ; and in a perfectly insulated electrometer of 
any size the effect does not take place unless the excited 
surface is brought so near the cap, as to occasion the gold- 
leaves to strike the sides of the instrument. 
I have elsewhere* stated some objections to the term in- 
duction as applied to electric phenomena; and I believe it 
will be quite unnecessary to expatiate on that subject, as a 
reference to ils literal interpretation by our best Lexico- 
griphers will sufficiently demonstrate its insufficiency and 
absurdity. 
T am, sir, yours, &c. 
Princes Street, Cavendish Square, G. J. SINGER. 
July 9, 1813. 
VII. On a supposed Error in M. Lapnace’s ‘* Mécanique 
Céleste.” 
To Mr. Tilloch. 
Sir,— An admirer of Laplace ventures to affirm, that the 
equation quoted by Mr, Thompson (in the Philosophical 
Magazine for last May), from the Mécanique Céleste, is 
by no means an error or oversight in the author of that in- 
comparable work, but may be easily deduced from the 
following train of reasoning on the subject. Should you 
think this elucidation worthy a place in your valuable work, 
by inserting it you will oblige, 
Sir, yours respectfully, 
MaATHEMATICUS. 
By referring to the Mécanique Céleste, it will be found 
ly —yd 
that Laplace has not put the equation c=3.m,—2—"* 
at 
: ‘—2x) (dy—dy')—&e. 
under the form ¢.3m=23.m.sm @=2) (eee ; but 
at 
tai! _ ante 
under the following, ¢.3m= 2mm’ ee ee ; r 
which is very different. For ¢ being a constant quantity, 
(x — x) (dy—dy')—&c. 
we haye Scm=c.Xm, but = t being a 
* Nicholson’s Journal, vol, xxxi. p. 216. é 
variable, 
