288 Mr. G. A. Hemsalech on the Origin of the 



In this case the mean values were: 



Furnace temperature after an 

 interval of 



Initial Furnace ^ — 



temperature. 10 seconds. 15 seconds. 



2700° C. 2200° 2100° 



Thus the values obtained with part of the current on are, 

 for the first 15 seconds and allowing for probable errors 

 which amount to about +50° C, practically the same as with 

 the current completely off. 



As has already been stated above, according to visual 

 observations the strong group at 4957 is the first to disappear 

 after the current is broken, and this fact agrees with my 

 former observations on the behaviour of these lines in the 

 spark. Now the photographic records show this group after 

 an interval of 10 seconds, but no longer after 15 seconds 

 from the moment of breaking the current. But, as my 

 observations indicate, the temperature of the furnace after 

 an interval of 10 seconds is down at 2300^, that is to say 

 well below the temperature at which these lines will appear 

 in ordinary circumstances. Hence the spectrum in this case 

 does not at all correspond to the temperature conditions of 

 the furnace, and it seems therefore not to be controlled by 

 temperature. Furthermore, when the current, instead of 

 being broken, was only reduced to 180 amperes so that a 

 slight potential gradient remained, the group at 4957 was 

 photographed after an interval of 15 seconds, i. e. at a 

 furnace temperature of only 2100°, and a trace is even 

 visible on a photograph taken 20 seconds after the drop in 

 current. These facts would seem to indicate that the 

 potential, which subsisted after the current had been dropped, 

 was still sufficient to appreciably prolong the life of this 

 group in spite of the low temperature of the furnace-tube. 

 The spectrum which remains visible after these lines have 

 disappeared is caused by thermo-chemical excitation and is 

 identical with that described in the preceding paper. 



All the observations recorded in this paragraph are quite 

 consistent with the view that the so-called high-temperature 

 furnace spectrum of iron is of electric origin. 



§ 5. Observations on the Furnace Spectra of Zinc, Copper, 

 Silver, Cobalt, and Nickel. 



Most of these spectra have already been investigated by 

 Dr. King, and my observations go to corroborate in a general 

 way his results. Thns, like Dr. King, I have been unable 



