C. GENERAL PHYSICS. 135 



quantities of the metals of undoubted purity, and his results 

 are the most reliable hitherto obtained. He has not only re- 

 moved all doubt with regard to some 28 spectral lines that 

 were hitherto known, but has increased the whole number 

 of these lines peculiar to these metals from 160 to 590. 



EFFECT OF TEMPERATURE AND PRESSURE OX THE SPECTRUM 



LINES. 



The question has often been discussed whether it is tem- 

 perature or pressure which causes the widening of the lines 

 in the spectrum of any gas. The following considerations 

 are adduced by Schuster as favoring the view that each sep- 

 arate molecule would show at all temperatures narrow lines 

 only, but that the shocks of the other molecules cause the 

 widening, which may therefore be considered as depending 

 rather upon pressure than temperature. Frankland and 

 Lockyer have found that if we increase the pressure of hy- 

 drogen while the electric current is passing through it, the 

 lines begin to expand until the spectrum becomes continu- 

 ous, and, finally, the current ceases to pass altogether. On 

 the other hand, Gassiot has observed that if we diminish the 

 pressure of hydrogen, its electric resistance diminishes, be- 

 comes a minimum, and then increases a^ain. "VVe are there- 

 fore compelled to accept Frankland and Lockyer's original 

 conclusion that pressure and not heat is the cause of the 

 widening of the line. Rep. Brit. Assoc, 1873, 39. 



NEW TABLES OF SPECTRUM LINES. 



The committee appointed by the British Association to 

 construct a catalogue of spectral rays state in their recent 

 report that the whole of their work is now finished and ready 

 for the printer, so far as regards the solar spectrum, while 

 the positions of the metallic lines, as determined by Thalen, 

 have been only partly reduced to uniformity with the rest 

 of the work. The tables presented by them are constructed 

 by throwing the solar lines into those groups which catch 

 the eye in observing the spectrum, and the position of each 

 line has been corrected for the dispersion of air. Both Kirch- 

 hoff's and Angstrom's scales will be given with the adopted 

 wave-lengths for each spectral line, so that it is hoped that, 

 when these catalogues are printed, observers will find in them, 



