432 Mr. H. Grubh on Telescopic Objectives and Mirrors. [April 2, 



and miglit watch narrowly every action tliat was taken, see every part 

 of tlie process, take notes, and so forth, and yet he could no more 

 expect to figure an objective himself, than a person could expect to be 

 able to paint a jDicture because he had been sitting in an artist's 

 studio for the same time watching him at his work. Experience 

 and experience only can teach any one the art, and even then it is only 

 some persons who seem to possess the power of acquiring it. 



A well-known and experienced amateur in this work declared his 

 conviction that no one could learn the process under nine years' hard 

 work, and I am inclined to think his estimate was not an exaggerated 

 one. 



True, it may be said that large objectives can be and are generally 

 turned out by machinery, but what kind of an objective would any 

 machine turn out if left to guide itself, or left to inexperienced 

 hands ? 



At the risk of being accused of working by what is generally 

 called the rule of thumb, I confess that conditions often arise, to meet 

 which I seem to know intuitively what ought to be done, what crank 

 to lengthen, what tempering is required of the pitch squares ; and yet if 

 I were asked I should find it very hard to give a reason for my so 

 doing which would even satisfy myself. 



I may safely say that I have never finished any objective over 

 10 inches diameter, in the working of which I did not meet with some 

 new exj)erience, some new set of conditions which I had not met with 

 before, and which had then to be met by special and newly devised 

 arrangements. 



A well-known English astronomer once told me that he con- 

 sidered a large objective, when finished, as much a work of art as a 

 fine painting. 



I have myself always looked upon it less as a mechanical opera- 

 tion than a work of art. It is, moreover, an art most difficult to 

 communicate. It is only to be acquired by some persons, and that 

 after years of toilsome effort, and even the most experienced find it 

 impossible to reduce their method to any fixed rules or formulae. 



[H. G.] 



