76 
Proceedings of Royal Society of Edinburgh [sess. 
Some Further Results obtained with the Spectro- 
heliometer. By Dr J. Halm. 
(MS. received November 15, 1905. Read November 20, 1905.) 
(. Preliminary Communication. ) 
In a paper published in vol. xli., part i., of the Transactions of 
this Society, entitled “ Spectroscopic Observations of the Rotation 
of the Sun,” I communicated the first results obtained with a 
spectroscope specially designed for the purpose of measuring the 
displacements of the solar lines on opposite limbs of the sun 
occasioned by the motions of the absorbing gases to or from the 
observer in consequence of the sun’s axial rotation. The investi- 
gation was originally undertaken with the view of ascertaining 
whether the peculiar law of surface rotation of the sun, first 
discovered by Carrington from the motions of solar spots, and 
afterwards confirmed by Duner from spectroscopic observations 
similar to my own, was, or was not, subject to alterations depend- 
ing on the general state of solar activity. The question proposed 
is admittedly of supreme importance for solar physics in 
general. Its solution depends, of course, in the first instance on 
the delicacy of the spectroscope employed ; the efficiency of which 
must be sufficiently proved before its results can be accepted with 
confidence. An attempt in this direction will be made in the 
present communication, in which I propose to discuss the whole 
bulk of my observations, now extending over fully four years, 
from a different point of view, which I think will enable us to 
arrive at definite conclusions with regard to the accuracy of these 
measurements. 
In order to be quite clear, I must describe the method employed 
in the observations. Without going again into the details of the 
instrumental arrangements, which are fully explained in the 
paper referred to, I may briefly say that the two spectra of 
exactly opposite limbs of the sun are thrown simultaneously into 
the focus of the viewing telescope, and there appear as indicated 
