INSTRUMENTAL DEVELOPMENT HALE 193 



with accurately controlled coelostats. Fixed telescopes and spectro- 

 graphs for solar work, whether horizontal or vertical, can be short- 

 ened if desirable by the use of telephoto lenses or by combinations 

 of mirrors. Both the ultra-violet and the less refrangible part of 

 solar and stellar spectra deserve more consideration than they have 

 received, and here especially improvements in the photographic 

 process, as well as in prisms and reflecting surfaces for the ultra- 

 violet, are greatly to be desired. No increase in the resolving power 

 of the grating is required for astronomical purposes, but more light, 

 obtainable from greater area of ruled surface, with concentration in 

 a single order, is- still needed for various researches. 



I shall not attempt in this paper to deal with less obvious possi- 

 bilities, or to discuss particular problems. Let me conclude with 

 the reminder that if instruments are important, " the man at the 

 eye end " is more important by far. In the Hindu treatise Siddlianta 

 Siromani, the astronomer Bhaskara, after describing a new form of 

 instrument, exclaims: "But what does a man of genius want with 

 instruments, about which numerous works have treated? Let him 

 only take a staff in his hand and look at any object along it, 

 casting his eye from its end to the top, there is* nothing of which 

 he will not then tell its altitude, dimensions, etc." If we can not 

 afford the sacrifice of precision which is here so lightly recommended, 

 we may at least remember that the mathematician embodies in him- 

 self the most powerful of all instruments for the solution of celestial 

 problems, and we may also find encouragement in the simple means 

 that have served in many classical researches. When Young laid the 

 foundations of the wave theory of light, and discovered the principle 

 of the interferometer, his*instruments were limited to a small mir- 

 ror, a few bits of paper and cardboard, some fine hairs, and a couple 

 of knife blades. If we are not mathematicians or experimental 

 physicists, and do not share in the use of large telescopes, we may 

 still find ample encouragement in the history of astronomical 

 progress. We have only to recall the splendid results obtained by 

 systematic observation with small telescopes by such men as Burn- 

 ham, Barnard, and Carrington, or those derived, also with small in- 

 struments, by men like Huggins, Secchi, and the pioneers in astro- 

 nomical photography, from the prompt and intelligent application of 

 methods and devices borrowed from the laboratory. 



