174 GENERAL CONDITIONS OF SCIENTIFIC RESEARCH. 



it is no small help towards the discovery or solution of 

 any problem to be first gf all apprised, in one way or 

 another, of the truth of its conclusion, and to know for 

 certain that it is not an impossibility that is being sought 

 after ; and that, therefore, the information and the cer- 

 tainty that the telescope had already been made were of 

 such use, that, without them, I should in all probability 

 never have made the discovery. To this I answer, that 

 the help given me by the information I received un- 

 doubtedly awoke in me the determination to apply my 

 mind to this subject, and without it I should very likely 

 never have turned my thoughts in that direction ; but 

 besides this, I cannot believe that the notice I had had 

 could in any way render the invention easier. I say, more- 

 over, that to find the solution of a problem, already thought 

 out and expressed, requires far greater genius than to 

 discover one not previously thought of;' (?) 'for in the 

 latter chance can play a great part, whilst the former is 

 entirely the work of reasoning. We know that the Dutch- 

 man, the first inventor of telescopes, was simply a common 

 spectacle-maker, who, handling by chance glasses of various 

 kinds, happened, at the same moment, to look through 

 two, the one concave, the other convex, placed at different 

 distances from his eyes, and in this wise observed the 

 effect which followed, and thus invented the instrument ; 

 but I, warned by the aforesaid notice, came to the same 

 conclusion by dint of reasoning, and since the reasoning is by 

 no means difficult, I should much like to lay it before you.' 

 ( This, then, was my reasoning : this instrument must 

 either consist of one glass, or of more than one ; it cannot 

 be of one alone, because its figure must be either concave 

 or convex or comprised within two parallel superficies, 

 but neither of these shapes alter in the least the objects 

 seen, although increasing or diminishing them ; for it is 



