288 Mr. G. A. Hemsalech and the Comte de Gramont on 



spark was attributed to increase of temperature. It appears, 

 however, that Sir Norman Lockyer originally used the term 

 " temperature " to include the possible effects o£ electrical 

 variations*. This fact seems to have been forgotten subse- 

 quently, for the word temperature has since been used solely 

 in its strictly thermal sense both by astronomers and spectro- 

 scopists, with the result that the enhanced lines (also called 

 spark lines or high temperature lines) play now a prominent 

 role in the temperature classification of the stars. One such 

 enhanced line — namely X-4481 of magnesium — has even been 

 strongly recommended for use as a stelJar thermometer. 



The first note of warning against the assumption that 

 changes of temperature are responsible for the emission of 

 enhanced lines seems to have been struck by Messrs. 

 Liveing and Dewar f, who observed the spark lines of 

 magnesium in an arc passing between thick rods of the 

 metal in air, nitrogen, hydrogen, and other gases. The con- 

 clusions arrived at by these spectroscopists are best restated 

 in their own words : " Our observations, however, render 

 doubtful the correctness of the received opinion that the 

 temperature of the spark discharge is much higher than that 



of the arc" ei Heat, however, is not the only form 



of energy which may give rise to vibrations, and it is 

 probable that the energy of the electric discharge as well as 

 that due to chemical change, may directly impart to the 

 matter affected vibrations which are more intense than the 

 temperature alone would produce." 



The appearance of spark lines in the arc in the presence of 

 hydrogen was again observed by Professor Crew J and by 

 Messrs. Fowler and Payne §. Messrs. Hartmann and 

 Eberhard, who obtained spark lines in an arc burning under 

 water, attributed their emission under these conditions to the 

 hydrogen released by electrolysis around the electrode ||. In 

 a further series of experiments Hartmann varied the currem. 

 strength in an arc passing between magnesium poles in air, 

 and obtained the astonishing result that the enhanced line 

 X 4481 becomes the stronger as the current strength is 

 lessened T". Similarly he obtained the spark lines of Zn, Bi, 

 and Pb, which do not show r in the carbon arc, in an arc 



* Nature, vol. lxxi. p. 400 (1905). 



t Liveing and Dewar, Proceed. Koy, Soc. vol. xliv. pp. 241-2 (1888). 

 I Henry Crew, Astrophysical Journal, vol. xii. p. 167 (1900). 

 § Fowler and Payne, Proceed. Roy. Soc. vol. lxxii. p. 253 (1903). 

 || Hartmann and Eberhard, Astrophysical Journal, vol. xvii. p. 229- 

 (1903). 



5[ Hartmann, Astrophysical Journal, vol. xvii. p. 270 (1903). 



