ASTRONOMICAL APPARATUS—HALB. 285 
problem of fluid prisms. If some one could take that question up and 
show us how to make very large prisms that would be essentially per- 
fect, they would accomplish a great advance. Lord Rayleigh told me 
the other day how he made some large fluid prisms that gave nearly 
theoretical resolution. By an extension of the same methods it seems 
likely that still larger prisms, suitable for the exacting requirements 
of photographic work, could be obtained. 
And so I might go on pointing out opportunities of various kinds, 
but I should tire you if I ventured to do so. We must not forget, 
however, that the possibility always exists of getting some entirely 
new method that will be quite as important as any application of 
the interferometer, or the echelon, or other instruments to which I 
have called attention. 
I hope I have shown that it is possible not merely to do work of an 
inferior quality, but to do work of the first quality, with small or 
inexpensive instruments; work that can not be duplicated or will not 
be duplicated with large instruments; in other words, that there is a 
splendid field for any man who wishes to accomplish results, wherever 
he may be situated, and however simple his means of research may be. 
I feel so strongly on this subject that I hope the suggestions I have 
made will not be entirely without effect. We need the ideas of men 
from all parts of the world; we need the contributions they can make; 
and we need them even more than we need larger instrumental means 
than we now possess.” 
