42 
PROCEEDINGS OE SOCIETIES. 
EOYAL I El SH ACADEMY. 
MONDAY, NOVEMBER 9, 1857. 
James Henthorn Todd, D. D., President, in the Chair. 
On the recommendation of the Council the following Eesolutions were 
adopted:— 
1. To authorize the Treasurer to pay a sum of £41 5s. 11^., to 
liquidate the Balance of the cost of printing the Museum Catalogue 
and arranging the Museum,—this sum being in addition to the sum of 
£250 voted on the 16th March last. 
2. That all moneys derived from the sale of the Catalogue, after 
the expenses of Advertising, &c., he devoted to the publication of the 
second part of that work. 
Eev. E. Carmichael read a paper on some Brief Methods in the In¬ 
tegral Calculus. 
Sir W. E. Hamilton gave an account of some researches of his own 
on the Theory of Definite Integrals. 
MONDAY, NOVEMBER 30, 1857. (Stated Meeting.) 
James Henthorn Todd, D. D., President, in the Chair. 
In consequence of the unavoidable absence of the author, the follow¬ 
ing paper by the Eev. T. E. Eobinson, D. D., was read by the President— 
ON THE DIETING POWERS OE ELECTRO-MAGNETS. 
This paper constituted the third part of Dr. Eobinson’s researches 
on the lifting power of the Electro-magnet. In it he examines the de¬ 
pendence of this power on the length and inductivity of the magnetic 
circuit which is formed when the poles are connected by a keeper. 
Whatever lessens the inductivity, lessens the magnetic power. If the 
circuit he incomplete, or if the middle of the keeper or of the magnet be 
brass, the power decreases to 0-70 or (H)8, or even to 0*02 of its normal 
amount. Plates of brass OH 2 thick interposed between the keeper and 
poles produce a similar effect; and even the minute interval which re¬ 
mains when they seem in contact is sufficient to destroy T ^- of the entire 
power. 
As iron does not transmit magnetic induction without diminution, 
the same decrease of power is caused by either increasing the circuit 
or placing the helices at a greater distance from the poles. In the first 
case, varying the circuit from 12 1 to 32 ; reduces the power to -J, in the 
second changing the distances from OH to 10 1 brings it to 0"87. 
If the helices be on one arm only, the poles are unequally excited, 
the adjacent one more, the remote less, than would be done by the same 
amount of excitation equally divided between the two arms. 
