158 
tion in economy, whatever the arrangement of the conduc- 
ting metal, or whatever the size of the battery.” The 
experiments of that paper indicate 36 foot lbs. as the maxi- 
mum duty for a grain of zinc in a Wollaston battery. Multi- 
plying this by 4 to bring it to the intensity of a Daniell’s 
battery, we obtain 144 foot lbs. Here, as in the experi- 
ments in the paper on Mechanical Powers of Electro-Mag- 
netism, Steam, and Horses, the actual duty is less than 
the theoretic; which is owing partly to the pulsatory 
nature of the current, and partly also to induced currents 
giving out heat in the substance of the iron cores of the 
electro-magnets; although these last were obviated as far 
as possible by using annealed tubes with slits down their 
sides. 
