214 M.G. Farmer on the Mechanical equivalent of Light. 
Art. XXIX.—WNote on the Mechanical Equivalent of Light; by 
Moses G. FARMER, Electrical Engineer 
In the October number of the L., E. and D. om 
Magazine is copied, from Poggendorff’ ’s Annalen, an article b 
we im Thomsen, of Copenhagen, on the mechanical equivalent 
of li 
His results show that about 13:1 foot-lbs, per minute repre- 
sent the mechanical seeping ae of a spermaceti candle, burning 
at the rate of 126} grs. per 
On om: ft of the 4th aE. J uly, 1863, there was exhibited 
by Mr. E. 8S. Ritchie, from the cupola of the State House in 
oawe, an electrical light, developed by the action of 250 Bun- 
sen cells, arranged in five rows of 50 cells. 
The Shtanaity of this light was estimated b f. Wm. B. 
Rogers, by direct a as equal to that os from 10,000 
to is, 000 standard candle 
If we consider the lecien motive force of a Bunsen cell as 
equal to the evolution of one cubic centimeter of mixed oxygen 
and hydrogen gases per minute in a circuit of which the total 
resistance is equal to that of 4400 ft. of a round wire j,th of 
an inch in diameter, made from electrotype copper; and if we 
assume also the internal ae poe of such a cell to be equal to 
15 ft. of such wire, (these about the average measurements), 
then the maximum available electrical energy, which these 250 
cells would oe woul 
(ns)? 1, (604400) 
: ges . Pw av alae = 80666666 
Since about 614 of these units of electrical energy are the 
6666 
pape of one unit of mechanical energy, we find aie 
000, foot-Ibs. as the mechanical energy equivalent to the 
light "iwvidepeds 
31000 
Dividing this by the estimated amount of light we get ~——5 a0 
13100 
=18 a or Sell foot-lbs. per minute as the mechanical 
uivalent of a candle light, a remarkably cl nt il 
the results of Prot ‘Pha ica a 
- Salem, Mass., Dec. 15, ciate 
