The Arc in Metallic Vapours in an Exhausted Space. 95 
certainty for the discrepancy between his results and those 
which I obtained, but I think it probable that the apparatus 
which he used may not have been sensitive enough to detect 
the alteration in the ionization. He mentions that at the 
higher temperatures the “ heated vessel appeared less active,” 
but attributed this to some other cause. It looks extremely 
probable that this was a genuine effect, but that the detecting 
instrument was not sensitive enough to show the effect to a 
sufficiently great extent. In the experiments which I did the 
electrometer used was a very sensitive one, giving a deflexion 
of about two thousand scale-divisions for a difference of 
potential of one volt between the quadrants. There was 
therefore no difficulty in detecting any alteration that might 
take place in the ionization. 
In conclusion I desire to express my thanks to Prof. Thomson 
for the kindly interest shown and advice given throughout 
the course of this investigation. 
Cavendish Laboratory, 
Cambridge, Nov. 5th, 1903. 



XU. Investigation of the Arc in Metallic Vapours in an 
Exhausted Space. (Contribution from the Research Labo- 
ratory of General Klectrie Co., Schenectady, N.Y.) By 
E. Wei1ntravus, Ph.D.* 
| Plates U11.-XI.} \ 
Introduction. 
J] HILE the carbon arc has been the object of a great 
number of investigations, the arc between mercury 
electrodes, which offers much simpler relations from a 
theoretical point of view, has so far been investigated but 
very little. We may distinguish between two distinct periods. 
In the first one the investigation was limited to the mercury 
are in air. Thomas Way (1857), (1861)f was probably the 
first to publish observations on a mercury are in air. One 
of his electrodes consisted of a stream of mercury, the second 
one of a mass of mercury or a piece of carbon, upon which 
the stream was caused to flow. 
Beginning at that’ time, a number of inventors occupied 
themselves with the arc, and a great number of patents were 
taken out on this subject. They were all founded on the 
same principle as the lamp of Way, and did not contribute 
anything essentially new to the art or science. 
* Communicated by the Author. 
T Dingler’s Polytechn. Journ. vol. clvii. p, 399 (1860) ; vol. clix. p. 46 
(1861); also U.S. Pat. 3345, Oct. 8 (1861); Eng. Pat. 2841 (1857). 
