278 COREESPONDENCE. 



perfect or complete, having all its working parts. If, in front of this, 

 we fix an extra " system," then we form a new compound instrument 

 or structui-e. Whether such a compound structure is to be called 

 an object-glass, is, of course, only a question of words, about which it 

 would be frivolous to dispute. Anything may be called anything. 

 But what is not a question of words, but of things, is, that the new 

 structm-e is not an object-glass in the same sense in which the word had 

 been used in this discussion ; inasmuch as it possesses different pro- 

 perties, and works under different conditions. What this difference 

 consists in I pointed out specifically in my former communication. 

 And that the assertion about the limitation of the angle had reference 

 to object-glasses, as commonly understood, is seen very plainly from 

 the original of the discussion ; for such are the object-glasses described 

 and figured in his large diagram by Dr. Pigott, who first introduced 

 the question and first fell into the error. 



The other part of Dr. Woodward's paper does not immediately 

 concern myself. I therefore only mention in passing that it contains 

 a similar oversight, which I have no doubt will be pointed out. 



Neither in this nor in his former paper has Dr. W. thrown 

 any new light upon this subject. And it is, I think, to be regretted, 

 that he has complicated a question in itself elementary, and of no 

 difficulty whatever, by coming forward without having first taken the 

 trouble to ascertain what exactly it was that had been asserted and 

 was denied. 



Your obedient servant, 



S. Leslie Beakey. 



" Fair Play " on Dr. Pigott. 

 To the Editor of the 'Monthly Microscopical Journal.'' 



224, KegejJt Street, Nov. 10. 



Sir, — Your correspondent, " Fair Play," is an ardent believer iu 

 and defender of Dr. Pigott's claims to be a discoverer in the difficult 

 subject of high-power definition. 



I take some interest in the subject, and would spare no pains to 

 inform myself of any real advance made. But because in many of 

 Dr. Pigott's contributions to the ' Monthly Microscopical Journal,' I 

 see but a sprinkling of valuable original matter embedded in a mass of 

 irrelevancy that suggests error when not defying comprehension, I 

 am led to a feeling of doubt as to the justice of his claims to be con- 

 sidered the inventor of a really successful Aplanatic Searcher. Will 

 " Fair Play," who is so well informed of Dr. Pigott's case, or still 

 better, will Messrs. Powell and Lealand tell us what shai"e Dr. Pigott 

 really had in the invention of the " Aplanatic Searcher " ? Whether 

 the basis of it was perchance some previous attempt of these renowned 

 opticians to construct a successful Amplifier — Dr. Pigott's share in the 

 invention not being the discovery of any new princij)le, but limited to 

 the suggestion of minor details ? 



The question of the practical utility of the Aplanatic Searcher is 

 probably decided in the negative, because, though Dr. Pigott has over 



