206 Conduction of Galvanic Electricity through Moist Air. 
for any length of wires and tube, and increase of surfaces in con- 
tact. A full realization of the principle appears in the fact, that 
* although the earth is a much poorer conductor than copper, mass 
for mass, yet upon the telegraphic routes, it is found that the 
earth is a much better conductor than the copper wires used, the 
mass of ‘the former being indefinitely greater than the latter. 
- These phenomena induced me to try the following experi- 
ment, in order to ascertain if the air might not act as a conduc- 
tor. The roof of the patent office building covered with copper, 
exposes to the air twenty-two thousand square feet of this metal, 
and thus affords an enormous surface for conduction. A wire 
was connected with the metal of the roof, another wire with a 
plate of zinc of about four square feet. 'The free ends of these 
two wires were connected with a galvanoscope of exceeding semsi- 
tiveness, and with matters thus arranged, the zine plate was insu- | 
lated from the earth and building, in the open air, and when the 
upper surface of the zine plate was moistened with water or what 
proved still better, acidulated water, the needle of the galvano- 
scope was deflected from two to five degrees. There was a slight 
drizzling rain at the time. Before the zinc plate was moistened 
- no action was noticed. The inference from this experiment 
seems safely to warrant the position that a moist atmosphere con- 
ducts galvanic electricity. Many years since, I proposed in this 
Journal a plan for ascertaining the level of the water in steam 
boilers consisting of a zine plate or a pair of plates, which should 
indicate the failure of water in the boiler by the cessation of 
action upon a galvanoscope placed in any convenient position 
outside the boiler. I have never had opportunity to test this de- 
vice, but was at the time somewhat apprehensive that pure steam 
might act as a conductor and thus defeat the invention. I have 
recently been informed, though not in a direct manner, that the 
experiment had been tried in Philadelphia and that the steam 
acted as a conductor. Whether dry air could act at all as a con- 
ductor remains yet to be ascertained, and I shall be able soon, 
; to put it to the test. Immediately after the above experiment 
was tried, the zinc plate was buried in the earth, other things re- 
maining the same. The galvanoscope is inside a window in the 
“second story, where I am enabled to watch it through most of 
the day. To my surprise as soon as connexion was made with 
— one being the copper soos, and d the other buried verti- 
ee ae 
