ON OtJR ICNOAVLEDGE OF SPECTKUM ANALYSIS. 



321 



(c) Sparli Spectra, 



Scale-nuii'iber Wave-length Oscillation-frequency 



1552-76 

 1638-37 

 1729-21 

 1782-9 

 1858-9 

 1873-0 

 1889-18 

 1916-17 

 1940-19 

 1958-29 

 19660 

 1997-4 

 1998-6 

 2026-37 

 2137-56 

 2195-49 

 2209-58 

 2365-44 

 2420-2 

 2519-39 

 2541-88 



If the observer is not familiar with the Fraunhofer hnes, oi has diffi- 

 culty in recognising the particular bright lines of the metals given in the 

 preceding list, the following plan is recommended : First observe accurately 

 the positions of the lines of the ' flame spectra ' given, and from these 

 construct an interpolation-curve ; then mark on the curve the wave-lengths 

 of the Fraunhofer lines, and so determine their' positions approximately on 

 the scale of the spectroscope. On directing the instrument to the sun or 

 to a bright cloud| the Fraunhofer lines will certainly be found at or near 

 these positions. Now let these Fraunhofer lines be read off as exactly as 

 possible, and from their positions, and those of the lines of the flame- 

 spectra, let a more accurate interpolation- cnrve be drawn, and let this curve 

 be used to find the positions of the lines of the spark-spectra. The final 

 curve should be drawn when the positions of these spark-lines have been 

 carefully observed. If it is not convenient to make use of the spark- 

 spectra, a very fair curve may be constructed from the lines of the flame- 

 spectra and from the Fraunhofer lines, but a little trouble in obtaining as 

 accurate a curve as possible will be well repaid. As a sample of what 

 may be done with a one-prism spectroscope and reflected scale, the follow- 

 ing numbers, taken from Lecoq de Boisbaudran, for the wave-lengths of 

 bismuth lines, are compared with Thalen's numbers .- — 



Lecoq de Boisbaudran 

 6130 

 6048 

 5719 

 5552 

 5268 

 5209 



Thale'n 

 6129-0 

 6050-0 

 5716-5 

 55530 

 5270-0 

 5208-0 



Lecoq de Boisbaudran 

 5144 

 5123 

 4724 

 4303 

 4259 

 4118 



Thale'n 

 5143-5 

 5123-5 

 4722-0 

 4302-0 

 4259-5 

 41190 



The lines from which Lecoq de Boisbaudran's interpolation-curve was 

 dra-wn are the following : — 



Scale-reading Wave-length Scale-readin. 



7680 

 7185 

 6867 

 6706 



Hydrogen 

 Cadmium 

 Zinc 

 Lithium 



83-71 

 86-25 

 88-00 

 9415 



Wave-length 

 6562 

 6438 

 6361 

 6102 



