APPENDIX E LXIX 
ago, but the field is also, comparatively speaking, unoccupied, as the 
number of observatories engaged in it can almost be counted on the 
fingers of one hand. A satisfactory beginning has been made in this 
work at the Dominion Astronomical Observatory by Mr. Plaskett, who 
adapted the Brashear universal spectroscope for accurate velocity deter- 
minations and has designed a new and in some respects original instru- 
ment which has been satisfactorily constructed in our own workshop 
and is now ready for practical work. With this instrument it is hoped 
to obtain results of great accuracy as all known sources of error have 
been either avoided or compensated for. The work so far accomplished 
with the original spectroscope has been the determination of the 
velocities of certain stars, the so-called “ standard velocity stars ” chosen 
by agreement among astronomers engaged in this class of work for 
periodical observation, and the determination of the velocity curves and 
the elements of the orbits of some spectroscopic binaries. Each of these 
binaries, which can be only recognized as being a double system from its 
variable velocity in the line of sight, requires some thirty or more obser- 
vations to satisfactorily determine an orbit and it is evident that half a 
dozen orbits will keep an instrument occupied for some considerable time. 
It is proposed further to observe the velocities of stars of a certain type 
of spectra which, not admitting from the character of the lines of very 
high accuracy of measurement, have been neglected by other observa- 
tories, but from which by using one form of the new instrument good 
results can be obtained. 
Not only is it proposed, when more assistance is obtained, to extend 
the spectroscopic work as above indicated, but micrometric and photo- 
metric observations with the equatorial telescope will also be undertaken ; 
the former, including measurements of the position angle and distance 
of selected double stars and other general micrometric work, and the 
latter, determinations of the light curves of variable stars. 
A start has also been made at solar research, a work which is most 
important in its practical bearing on terrestrial climatic action. <A 
photograph of the sun’s surface is made every unclouded day, on a scale 
of 772 inches to the sun’s diameter, to form a record of the solar dis- 
turbances so far as indicated by the sun spots present. This is effected 
by an enlarging camera attached to the equatorial telescope. The scope 
of this work is, however, to be much extended by the erection during the 
present season of a shelter for a horizontal ccelostat telescope. 
The instruments will consist of a cœlostat with a 20 inch plane 
mirror driven by clock work at such a rate as to reflect a beam of light 
from the sun in a constant direction to a secondary plane mirror 20 
Proc., 1906. 5. 
