DISTRIBUTION OF INTENSITY IN BROADENED SPECTRUM LINES. 
487 
apparent cases of reversal are not in fact spurious, having no relation to true reversal, 
clue to absorption. 
Finally, the different character of lines of the same series in the spectra of the 
alkaline earth metals which lias been noted by Koyds # may be expected to fall into 
line with their electrical resolution when the necessary data are available. 
(XI.) Ultraspectroscopic Analysis by Means of the Neutral Wedge. 
It may be mentioned that the neutral wedge as an accessory to the spectroscope 
virtually increases its resolving power. The intensity distribution of the image of an 
infinitely narrow line, as seen in a spectroscope of known resolving power, is precisely 
defined, and analysis by means of the neutral wedge enables us to build up a system, 
both as regards position and intensity, which conforms with the curve experimentally 
found. It is therefore evident that with this accessory the practical resolving power 
of the spectroscope depends only on its dispersion, and is independent of the 
theoretical purity of the spectrum. In conjunction with the interferometer it may 
be expected to give results beyond the attainment of pure spectroscopic analysis. 
It may reasonably be hoped that the application of such methods may enlarge our 
knowledge of the structure of the finest spectrum lines. 
(XII.) Summary. 
(1) A method has been described, involving the use of a neutral-tinted wedge, 
by means of which the actual distribution of intensity in broadened spectrum lines 
can be accurately measured. 
(2) With this arrangement quantitative measurements of the hydrogen line H a 
have been made, and qualitative observations of other lines of hydrogen, helium, and 
lithium. 
(3) The intensity distribution of lines, broadened by condensed discharges and 
at high pressures, does not follow the well-known probability law, which is known 
to obtain under certain specified conditions. 
(4) The broadening of H a is symmetrical. 
(5) The most general characteristic of all the curves obtained is that their 
curvature is away from the axis perpendicular to the wave-length scale. It is shown 
that even in the case of a simple curve, such as that found for H a , this is inconsistent 
with the view that a single component is involved. 
(6) The existence of more than one component is in accordance with the view that 
the electrical resolution of the lines is the origin of their broadening. 
(7) On the supposition of several components, symmetrically distributed about the 
* Loc. cit. 
