Dr» WoUmMs Microscopic Doublet. 249 



as I would be done by myself, and shall proceed to a rectifica- 

 tion of divers matters discussed by him, with precisely the 

 same delicacy and respect to his dignity and genius which I 

 should have observed had he been still living, (though, strictly 

 speaking, such men as Wollaston never die.) 



Dr. Wollaston's paper being hastily thrown together in 

 paragraphs, I shall number them, for the sake of convenient 

 reference ; in the original, the text contains nineteen, and the 

 Appendix three more. Dr. Wollaston seems to have been 

 animated by a most laudable ambition of surpassing every 

 thing which has yet been done in the way of improving micro- 

 scopes, and of presenting to opticians not only a better article 

 than has yet been produced, but a cheaper one also (Par. 6) : 

 in this most praiseworthy design, he assures us he has 

 thoroughly succeeded (Par. 4 and 18), and, moreover, con- 

 densed his instrument into a box four inches square (App. 

 Par. 2.) 



As there is not much connection between the different pas- 

 sages of his paper, I shall notice them pretty much in the 

 order in which they are written. Touching the instrument 

 itself, it may be divided, like all other microscopes, into 1st, 

 its optical part ; 2nd, its illuminative apparatus ; 3rd, its me- 

 chanical arrangement for applying the object, and adjusting 

 the focus, &c. 



Par. 2. •• In the illumination of microscopic objects, whatever light is 

 collected and brought to the eye beyond that which is fully commanded 

 by the object glasses, tends rather to impede than to assist distinct 

 vision." 



I'Par. 3. " My endeavour has been to collect as much of the admitted 

 light as can be done, by simple means, to a focus in the same plane as 

 the object to be examined." 



The principle laid down in Par. 2 is undoubtedly correct, 

 at least if taken in a certain sense, and unconnected with the 

 following Par. 3. It is well known, that the aberration of all 

 optical instruments is most sensible with brilliant objects, or 

 with others rendered so artificially. Thus, it may be said, 

 that a telescope which is unable to command or define a large 

 star, will nevertheless reduce a small faint one to a brilliant 

 dot, and an outsized reflector, which cannot, perhaps, give any 



