Galvanic Electricity through Moist Air. 363 



the length of ten miles would give a surface of 550 square 

 feet, while the length of the conductor would be only the 

 thickness of the material, and a constant quantity, for any 

 length of wires and tube, and increase of surfaces in contact. 

 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 phaenomena induced me to try the following expe- 

 riment, in order to ascertain if the air might not act as a con- 

 ductor. 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 conduc- 

 tion. A wire was connected with the metal of the roof, an- 

 other wire with a plate of zinc of about four square feet. The 

 free ends of these two wires were connected with a galvano- 

 scope of exceeding sensitiveness, and with matters thus ar- 

 ranged, the zinc plate was insulated from the earth and build- 

 ing in the open air, and when the upper surface of the zinc 

 plate was moistened with water, or what proved still better, 

 acidulated water, the needle of the galvanoscope 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 zinc 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 conve- 

 nient position outside the boiler. I have never had oppor- 

 tunity to test this device, but was at the time somewhat ap- 

 prehensive 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. Whe- 

 ther dry air could act at all as a conductor 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 remaining 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 the plates, 

 one being the copper roofing and the other buried vertically 



