Carpenter on the Microscope. 349 



afforded by the assemblage of instruments at the late Exhibi- 

 tion, or by any other means of instituting an extended com- 

 parison of the operation of instruments of different kinds. 



The most important addition to the microscope since Dr. 

 Carpenter last wrote, is undoubtedly the binocular arrange- 

 ment of Mr. Wenham, which marked an enormous advance 

 upon the earlier methods adopted by that gentleman, or upon 

 those employed in the more complicated and less serviceable 

 form adopted by Nachet. At first the new binoculars were the 

 subjects of exaggerated praise, and their admirers appeared to 

 fancy that no one had ever seen objects in relief without their 

 aid. These notions have by this time sobered down, and the 

 binocular takes its permanent place as an addition to, not a 

 substitute for, monocular patterns. To some observers its utility 

 is much greater than others ; those whose eyes are the best 

 matched in point of focus and power being the best suited ; 

 while other persons — some eminent naturalists amongst them — ■ 

 do not find it of the slightest use. Most people, however, will 

 be helped by it for certain objects, and will agree with the 

 modified eulogium pronounced by Dr. Carpenter, who observes: 

 " It is requisite to bear in mind, that as the special purpose of 

 the binocular microscope is to convey to the mind the notion 

 of the solid forms of objects, of which some parts approximate 

 to the objective more closely than others, the rays proceeding 

 from the most projecting parts cannot be so nearly brought to 

 the same focus with those from the mediary, as to produce even 

 a tolerably distinct image of both at once ; and it is moreover 

 to be recollected, that when high powers are being employed, 

 and especially such as are of large angular aperture, the smallest 

 departure from exactitude in the focal adjustment gives indis- 

 tinctness to the image. It seems to be only with objectives of 

 comparatively low power and small angular aperture that images 

 most suited for the production of stereoscopic effects will be 

 produced; but for certain classes of objects this mode of exhibi- 

 tion is admirably adapted.-" 



Without depreciating the " binocular," we may remark that 

 a still greater boon to science wouldbe the construction of a micro- 

 scope adapted to take in a very large field, so as to facilitate the 

 study of marine and fresh- water animals or vegetables in an 

 aquarium, or large zoophyte trough. It is extremely difficult 

 to determine many interesting points of development unless 

 the objects can be watched under circumstances that make 

 them quite at home ; and although Mr. Warrington's portable 

 microscope can be brought to bear upon any vessel, it has the 

 defect of instruments intended for minute investigation, and 

 the field is not one-third of the diameter that could be advan- 

 tageously used. 



