320 



BEPOET — 1881. 



The best map of the bright lines of the metals is that of Thalen ' (upon 

 the scale of wave-lengths), who, however, has employed poles of the metals 

 themselves and higher coil-power than is likely to be used in ordinary 

 laboratory work. 



Other modes of ignition, which, however, will be employed for the 

 most part only for special researches, are furnished by the oxy-hydrogen 

 blowpipe and by the electric arc. The differences in the spectra obtained 

 by employing these different methods of ignition may be shortly accounted 

 for by the different temperature to which the substance is heated — at 

 low temperatures the spectra of compounds are obtained which at higber 

 temperatures are resolved into their elements. The Bunsen flame gives 

 the lowest temperature, the oxy-hydrogen flame next, then the spark from 

 a small coil without a Leyden jar ; then comes the electric arc, the tem- 

 perature of which increases with the number of cells employed ; then the 

 spark obtained with an induction coil and small jar, the temperature of 

 which is increased up to the highest point obtainable by increasing the 

 size of the coil and jar employed. 



The following list of lines will be found useful in constructing the 

 curve of wave lengtbs for a one-prism spectroscope. The wave-lengths 

 are given in tenth-metres ^ (or ten-millionths of a millimetre) ; there is 

 also given the approximate position of the line on Bunsen's scale, and the 

 reciprocal of the wave-length, or ' oscillation-frequency ' — I.e. the number 

 of waves in one millimetre. There are many advantages in using these 

 ' frequencies ' instead of the wave-lengths themselves, as will be after- 

 wards explained. 



(rt) Flame S/Jeotra. 

 Wave-length. Osnillation-frequency. 



6707-3 

 .5896-8 "• 

 5890-7^ 



ThalUum . 678 . 53511 



Magnesium'' 74-5 . 5184-2 



Strontium 105-5 . 46090 



Lithium 

 Sodium 



Scale-number. 

 . 31-8 



. 500 



Mean 5893-7 



A . 

 B 



C . 



D . 



E 



b, . 



b, . 

 bj and b^ 

 F 



G . 



H, . 



H„ . 



17-5 

 28-9 

 35-0 



50-0 



70-9 



74-5 



74-8 



75-0 



90-0 



127-3 



161-2 



165-7 



- Mean 5893-7 



(b) Frannliofer Lines 



76061 



6869-1 



6563-9 



5896-8 "I 



5890-7 J 



5270-6 



5184-2 



5173-6 



6169-1 



4862-1 



4308-5 



3969-2 



3934-1 



] 490-9 ■* 



] ^^2'?^ ) Mean 1696-7 

 169/-o8/ 



1868-8 



1928-94 



2169-7 



1314-74 



1455-82 



1523-48 



1695-841 



1697-58 J 



1897-31 



1928-94 



1932-89 



1934-56 



2056-73 



232102 



2519-39 



2541-88 



Mean 1696-7 



' Nitva Acta Reg. Soc. Sc. Upsal., Third Series, vi. TJpsala. W. Schultz, 1868. 



- A ' tenth-metre ' is (i) " metre. 



^ Least refrangible line of the (J) group, seen in the flame of burning magnesium. 



■* The lines of which the oscillation-frequencj" is given to two decimal places are 

 found in Angstrom's map, and in the B.A. catalogue of oscillation-frequencies ; those 

 •which have only one decimal place are given on the authority of Thalen. His 

 numbers have been corrected for the small differences between his tables and the 

 table given in Angstrom's work (' Kecherches sur le spectre solaire,') p. 31, and also 

 for the dispersion of air so as to give the wave-lengths in vacuo. All the numbers in 

 the above table refer therefore to the vacuum. 



