



Ch 
i taacearn a 
LIX. On the Analysis of Bright Spectrum Lines. By JAMES 
Barnes, M.A., 1851 Exhibition {Scholar, Fellow of Johns 
Hopkins University*. 
‘Plates XXV. & XXVI.} 
T is well-known that a change is produced 1 in the wave- 
length and distribution of light in the lines of the 
spectrum of metallic vapours and gases when different 
external conditions are introduced. In most cases these 
changes were first observed and measured by means of the 
Rowland erating. Recently, however, these effects have 
become more readily observable through interference methods, 
in which the interference-bands are produced with large 
differences in the paths of the rays. 
Michelsont, by aid of his interferometer, resolved the 
important lines in the radiations of some vapours and gases 
rendered luminous in vacuum-tubes, and he has studied these 
radiations ina magnetic field. With his echelon spectroscope 
he has investigated the same subjects. Fabry and Perot t 
with their interferometer have investigated the radiations 
from yapours in the electric are and in vacuum-tubes, and 
have applied their method for an exact determination of the 
wave-length of some of the lines in the spectrum of the iron 
are and of the dark lines in the sun’s spectrum. Lummer §, 
also by an interference method, has studied the same radia- 
tions, particularly those from mercury, and has separated its 
prominent lines into many components. 
When one compares the results of these investigations the 
agreement is not very satisfactory. Not only do the number 
and intensity of the components differ, but the distances 
between the components do not agree. 
The work presented in this paper was undertaken at the 
suggestion of Professor Ames. The objects of the work were : 
to study interferometer methods ; to obtain, if possible, more 
consistent results as to the constitution of the lines ; and 
to determine the changes produced in the components under 
various conditions. Michelson remarks in one of the papers 
cited :-—‘‘ Still, in many eases, the range of visibility due to 
slight variations in the conditions shows that the behaviour 
of each substance must be carefully studied under all possible 
* Communicated by ahi oe J.S. Ames. 
+ Phil. Mag, [5} xxxi. p. 338 (1891) ; xxxiv. p. 280 (1892). 
{ Ann. de Chim. et Phys. xii. p. 459 (1897) ; xvi. pp. 115 & 289 (1899) ; 
Astrophys. Journ. ix. p. 87 (1899). 
§ Verhdlgn.d. D. Phys. Ges. iii. p. 85 (1901) ; Phys. Zeit. (3) viii. p. 172 
(1902). 
