68 MR. J. P. JOULE ON THE LIFE AND WRITINGS 



desirable to make, had the opportunity of observing, for the 

 first time, a highly important fact, which he describes in the 

 following words: — " The battery was in series of one hundred 

 and sixty pairs. I brought the tip ends of the polar wires 

 (copper wire, one-tenth of an inch diameter) into contact, end 

 to end, then withdrew them gently and very gradually from 

 each other, keeping the flame in full play between them, till 

 they were separated about one-fourth of an inch. In a few 

 minutes the positive wire got red hot for half an inch, but the 

 negative wire never became red. I repeated this several 

 times in order to be convinced of the fact. I next laid the 

 wires across one another, and bronght them into contact about 

 an inch from- the extremities, and separated them as before. 

 In a short time the whole of that part of the positive wire 

 from the point of crossing to the extremity became very red 

 hot, but the negative end never got even to a dull redness ; 

 it was certainly very hot, but never higher than a black heat. 

 I next increased the length of the ends of the wires exterior 

 to the circuit, and eventually heated two inches of the positive 

 wire to a bright redness, but no such heat took place on the 

 other wire. Thus satisfying myself that I was not mistaken, 

 I called Mr. Mason to come and look at it ; and, after 

 satisfying that gentleman by an experiment or two, we called 

 Mr. Gassiott and Mr. Walker to come and witness the novel 

 phenomenon," Mr. Sturgeon considered that the heat was 

 driven along bodily by the electric current, so as to accumu- 

 late at the point whence the discharge across the air takes 

 place, an hypothesis which cannot be entertained at the 

 present day. The true explanation of the phenomenon is 

 most probably that advanced by Professor Thomson, viz., 

 that in thermo-electric arrangement air stands in the same 

 ratio to copper as bismuth does to antimony. Whence 

 heat is evolved by electricity passing from copper to air, 

 but cold by the reverse action. 



Porrett had discovered a disturbance of the hydrostatic 



