192 MANAGEMENT OF THE MICROSCOPE. 



dese' of Mr. Ealfs, we find sure reason to conclude that these re- 

 searches must have been made with the instrumentahty of lenses, 

 which would in the present day be regarded as of very limited 

 capacity. I hope that, in these remarks, I shall not be under- 

 stood as in any way desirous to damp the zeal of those, who are 

 applying themselves to the perfectionizing of achromatic objec- 

 tives. I regard it as a fortunate thing for the progress of science, 

 that there are individuals whose tastes lead them to the adoption 

 of this pursuit ; who stimulate our instrument-makers to go on 

 from one range to another, until they have conquered the diffi- 

 culties which previously baffled them ; and then apply themselves 

 to find out some new tests, which shall offer a fresh difficulty to be 

 overcome. But it is not the only, nor can I regard it as the chief 

 work of the Microscope, to resolve the markings upon theDiato- 

 macese, or tests of the like difficulty ; and although I should con- 

 sider this as the highest object of ambition to our makers, if the 

 performances of such lenses with test-objects were any fair mea- 

 sure of their general utility, yet as I think that I have demon- 

 strated that the very conditions of their construction render them 

 inferior in this respect for the purposes of ordinary microscopic 

 research, I would much rather hold out the reward of high ap- 

 preciation {we have no other to give) to him who should produce 

 the best working microscope, adapted to all ordinary requirements, 

 at the loivest cost. It does not seem to me an unapt simile, to 

 compare the devotees of large angular apertures to the gentle- 

 man of the ' turf.' It is, I believe, generally admitted, that the 

 breeding of a class of horses distinguished by speed and ' blood,' 

 which is kept up by the devotion of a certain class of our country- 

 men to the noble sport of racing, is an advantage to almost 

 every breed of horses throughout the countiy ; tending, as it 

 does, to develope and maintain a high standard in these particu- 

 lars. But no one would ever think of using a race-horse for a 

 roadster or a carriage-horse ; knowing well that the very qualities 

 which most distinguish him as a racer, are incompatible with 

 his suitableness for ordinary work. And so I think that the 

 ' breeders' of first-class Microscopes (if I may so designate 

 them) are doing great service, by showing to what a pitch of per- 

 fection certain kinds of excellence may be carried, and by thus 

 improving the standard of ordinary instruments ; notwithstand- 

 ing that, for nearly all working purposes, the latter may be prac- 

 tically superior." 



102. Test Objects. — It is usual to judge of the optical perfection 

 of a Microscope, by its capacity for exhibiting certain objects, 

 which are regarded as tests of the merits of its object-glasses; 

 these tests being of various degrees of difficulty ; and that being 

 accounted the best instrument, which shows the most difficult 

 of such tests. Now it must be borne in mind, that only two out 

 of the four qualities which have been just enumei-ated, — namely, 

 defining power, and resolving power, — can be estimated by any 



