24 PRESIDENT’S ADDRESS. 
and if possible by another observatory in the southern hemisphere, and 
by three observatories in the northern, would be regarded by astronomers 
of the future as the most valuable contribution that could be made to 
astronomy of the present day. Taken in conjunction with the astro- 
graphic survey of the heavens now so far advanced, it is an opportunity 
that if lost can never be made good ; a work that would grow in value 
year by year as time rolls on, and one that would ever be remembered 
with gratitude by the astronomers of the future. 
But for the solution of the riddle of the universe much more is 
required. Besides the proper motions, which would be derived from the 
data just described, we need for an ideal solution to know the velocity in 
the line of sight, the parallax, the magnitude, and the spectrum-type of 
every star. 
The broad distinction between these latter data and the determination 
of proper motion is this, that whereas the observations for proper motion 
increase in value as the square of their age, those for velocity in the line 
of sight, parallax, magnitude, and type of spectrum may, for the broader 
purposes of cosmical research, be made at any time without loss of value. 
We should therefore be most careful not to sacrifice the interests of the 
future by immediate neglect of the former for the latter lines of research. 
The point is that those observatories which undertake this meridian work 
should set about it with the least possible delay, and prosecute the pro- 
gramme to the end with all possible zeal. Three observatories in each 
hemisphere should be sufficient ; the quality of the work should be of the 
best, and quality should not be sacrificed for speed of work. 
But the sole prosecution of routine labour, however high the ultimate 
object, would hardly be a healthy condition for the astronomy of the 
immediate future. The sense of progress is essential to healthy growth, 
the desire to know must in some measure be gratified. We have to test 
the work that we have done in order to be sure that we are working on 
the right lines, and new facts, new discoveries, are the best incentives to 
work. 
For these reasons Kapteyn, in consultation with his colleagues in 
different parts of the world, has proposed a scheme of research which is 
designed to afford within a comparatively limited time a great augmenta- 
tion of our knowledge. The principle on which his programme is based is 
that adequate data as to the proper motions, parallaxes, magnitudes, and 
the type of spectrum of stars situated in limited but symmetrically dis- 
tributed areas of the sky, will suffice to determine many of the broader 
facts of the constitution of the universe. His proposals and methods are 
known to astronomers and need not therefore be here repeated. In all 
respects save one these proposals are practical and adequate, and the 
required co-operation may be said to be already secured—the exception is 
that of the determination of motion in the line of sight. 
All present experience goes to show that there is no known satisfactory 
method of determining radial velocity of stars by wholesale methods, but 
