of Magnesium, Copper, and Manganese. 315 



manganese, which in the air-coal gas flame are emitted by 

 the mantle above the cone, appear all as long lines in the 

 single plate furnace. This fact confirms their status as 

 temperature lines. §§ 6, 1, and 8. 



§ 10. Concluding Remarks. 



The very definite grouping of the spectrum lines of metal 

 vapours according to character, as revealed by the selective 

 actions of thermo-electrical and thermo-chemical excitation 

 with the single plate resistance-furnace, makes it appear 

 hopeful that the new method of spectroscopic analysis 

 developed in the course of this investigation will be of some 

 help in the search for related lines in the case of metals 

 ipossessing complicated line spectra. Furthermore, the 

 remarkable agreement which has been shown to exist 

 between the spectroscopic effects produced by thermo- 

 electrical and chemical excitations goes to mark out the 

 single plate furnace as a valuable means of both checking 

 and supplementing the results given by flames. In parti- 

 cular this type of furnace provides the possibility of singling 

 out the characteristic line emission which accompanies the 

 decomposition of a chemical compound under temperature 

 conditions unattainable in flames. Thus at a very high tem- 

 perature and with the aid of electric actions the plate furnace 

 performs the same function as the air-coal gas flame at a 

 comparatively low temperature with the help of chemical 

 actions. In this respect the red fringe may be regarded as 

 the electrical analogue of the explosion region ; in both, the 

 line emission by metal vapours is connected with the breaking 

 up of compound molecules, but the manner in which this is 

 brought about is probably different in each. The resul ting- 

 luminous effects, however, are evidently of the same order in 

 both, as has been so clearly established by these experiments. 



The fact that an electric current or — what may be regarded 

 as its equivalent — a drift of electrons travelling under the 

 action of a relatively feeble electric field is capable of strongly 

 exciting characteristic spectrum radiations in metal vapours, 

 may have some important bearing on certain astrophysical 

 problems. Thus it is conceivable that at the very high tem- 

 perature prevailing in the lower strata of the chromosphere 

 or in the reversing layer an electric field of only a very minute 

 fraction of a volt per centimetre may suffice to stimulate 

 spectroscopic effects comparable to those which the relatively 

 much more intense electric fields of our laboratory furnaces 

 produce at considerably lower temperatures. 



Manchester, May 1920. 



Y2 



