434 SCIENCE PROGRESS 



The chief difficulty is to determine how much of the two main 

 items, the maintenance of the Observatory and the salary of the 

 Director, are to be credited to this particular work. In the 

 above statement the whole of the Professor's salary has been 

 set down, not even deducting income tax; but some of it must 

 be credited to teaching and other duties which fall on him as on 

 his colleagues. 



The same difficulty arises in a smaller degree about the 

 second item in the list, as the assistants have by no means 

 confined themselves entirely to work on the star map. As the 

 best estimate possible under the circumstances we may take 

 ;^20,ooo perhaps as the Oxford contribution to this great work ; 

 and as there are seventeen other contributors, many of whom 

 are not working under such favourable conditions, the total cost 

 will be at least half a million sterling. 



These estimates have not been made and quoted for sensa- 

 tional purposes but with the very definite object of showing 

 the necessity for care in procedure. We are dealing with big 

 figures — long periods of time and large sums of money. We 

 must on the one hand spend money freely to save time : we 

 must make a map on a large scale, so that we may determine 

 the movements of the stars within a reasonable period. On 

 the other hand, since every detail of the process will be 

 repeated thousands or even millions of times, we must be 

 extremely careful in settling the details so as to save expense. 

 If one figure will suffice rather than two, the diff'erence may 

 seem trivial in a single instance, but when multiplied a million 

 times will constitute a serious item of unnecessary expenditure. 

 If one measure will give fair accuracy, then before yielding to 

 the temptation to increase the accuracy a little by making a 

 second measure, we must remember that we are multiplying 

 the total cost of measuring by two and consider carefully 

 whether the extra expense is justified ; and that we are also 

 multiplying the time required for completing the work by 

 two, and consider carefully whether the completion can be so 

 long delayed without serious disadvantage. When confronted 

 by such problems, the different contributors to the scheme 

 have naturally differed in their solutions. At Oxford we have 

 throughout fixed our attention on getting the work done as 

 quickly and economically as possible, consistently with certain 

 rules laid down by the International Committee ; nevertheless 



