THE PLANET MARS 127 



observers have been led here is both instructive and startling, 

 as they have found that, even under conditions so good as to 

 be incredible to those who have not seen them, no advantage 

 in definition is gained by dilating the aperture beyond eighteen 

 inches ; and when the conditions are less than the best, a very 

 perceptible loss of detail occurs. 



It seems probable that until some better climate be found, no 

 very substantial advance can be made in the effective power of 

 our instruments but as yet so little is known of the conditions 

 prevailing in out-of-the-way localities that it is quite likely that 

 diligent search may reveal a better place. Meanwhile we must 

 console ourselves with the knowledge that the optician has done 

 all he can for the problem, having made telescopes much larger 

 than the astronomer can use profitably. 



Having made this discovery, we must turn our thoughts 

 from the lens at the big end of the telescope to the man at the 

 small end, whose qualifications must now be examined. 



Only those whose profession is the use of their eyes can 

 realise how much training is both necessary and possible and 

 how much the degree of proficiency attained depends upon the 

 nature of the training. Just as musicians are called upon to 

 learn different instruments, so astronomers are called upon to 

 view different objects. 



There are two main divisions of visual astronomy — stellar 

 and planetary — differing from each other in as many essentials 

 as do fiddling and piano playing. In the case of a star, the 

 observer knows what he is seeking — namely a small disc of 

 light ; all he needs is to see that the star is there. 



The case of a planet is different. The disc is there, it 

 cannot escape notice but we are not concerned with it but with 

 its parts. The glimpses of detail which our troubled atmosphere 

 permits us to obtain are but momentary and therefore one of 

 the first essentials is that the observer shall cultivate quickness 

 of perception as well as acuteness in discrimination. Herein 

 lies the fundamental difficulty of Martian observation which 

 only long practice can surmount. 



When the conditions are not the best, only the very quick 

 observer will be able to see anything properly. The canals may 

 flash into sight repeatedly without the inexperienced observerever 

 perceiving them. He must wait for one of those rare occasions 

 when the detail is steadily visible during a second or two, in 



