373 
with a large voltaic battery . 
weight of mercury, in the circuit, and connected together by 
a platina wire of such size and length as to be kept constantly 
ignited. The mercury in the cup connected with the zinc 
end of the battery, attained in 20 minutes the temperature of 
121 0 ; that in the other cup 112 0 . 
The battery, even in its most active state, communicated 
no charge to the Leyden phial. 
I give the following experiment, the last with which I 
shall occupy the time of the Society, without comment. I 
separated all the zinc from the copper plates, by dividing the 
leaden straps that united them ; and then by means of other 
leaden straps, I connected all the zinc plates together as one 
plate, and all the copper plates in the same manner ; thus 
reducing the whole battery to only two plates, each present- 
ing a surface of 1344 square feet, reckoning the copper sur- 
face as only equal to the zinc. When the plates, thus 
arranged, were suspended, quite out of contact with the acid, 
a communication was made between the two metallic surfaces 
by means of a platina wire ^-^^th of an inch diameter, and 
about -^th of an inch long, with every possible attention to 
ensure a perfect contact; but, although the experiment was 
made in the dark, not the slightest appearance of ignition was 
perceptible in the minute wire by which these extensive sur- 
faces were connected. It is known, I believe, to almost every 
member of this society, that Dr. Wollaston has shown, with 
the delicate apparatus invented by him, that a platina wire, 
of the same dimensions as that just mentioned, is instantly 
ignited by a single pair of plates one inch square, on being 
immersed in a diluted acid. The ratio of the areas of the 
plates of the respective batteries is as 1 to 48384. When the 
