MICROSCOPE. 



349 



and its portability is a great recommendation. 

 The one in our own possession is packed, with 

 its tripod, into a box whose outside dimensions 

 are 7 5 inches by 5, and its depth only 2, and 

 this also contains a short body with meniscus 

 eye-piece, four ordinary magnifiers, and three 

 doublets and triplets, which may be used 

 singly or as objectives, illuminating lenses and 

 speculum, aquatic boxes, and other small ap- 

 paratus, the weight of the whole being no 

 more than 2 Ibs, although a magnifying power 

 of 450 diameters, with sufficient penetration to 

 exhibit the markings on the Podura, and with 

 perfect steadiness, may easily be obtained by it. 



The instruments we shall now describe are 

 not adapted for use in any other way than as 

 compound microscopes. Their size and weight 

 are such as would render them far less conve- 

 nient than the smaller forms already described 

 for use with simple lenses, although there is no 

 other reason why they should not be thus em- 

 ployed. Every constructor of microscopes has 

 his own favourite model ; and there are few re- 

 cently made instruments of the highest class 

 which do not possess some particular recom- 

 mendations. Amidst the numerous claimants 

 to our notice, we shall select two; of which 

 the first is the form adopted by one of the best 

 constructors of achromatic objectives in this 

 country ; and the second is the one which we 

 have ourselves had in use for several years, 

 and which we do not desire to lay aside for 

 any we have seen. With respect to the former, 

 our limited space compels us to refer to the 

 article Microscope in the Penny Cyclopaedia, 

 where a delineation and full description of Mr. 

 Ross's Microscope will be found.* 



We shall now describe the microscope 



* [Without wishing in the least degree to detract 

 from the merit of Mr. Ross's microscope, (to 

 which, on the contrary, he bears willing testi- 

 mony ,) the Editor deems it but justice to refer 

 to a very beautiful instrument constructed by Mr. 

 Powell, which lie has employed for some time, and 

 which is also used by several observers in this city. 

 The body of tlie microscope moves on a triangular 

 bar, bavins; a bearing of three inches, which ren- 

 ders it ve.-y steady. The coarse adjustment is ob- 

 tained by a rack and pinion, attached to which are 

 two large milled heads, which allow of the body 

 being adjusted with either hand. The fine adjust- 

 ment has also two milled heads, only two inches 

 apart from the coarse one, and their axis being 

 horizontal and parallel to each other, renders the 

 motion of the hand from one to the other perfectly 

 easy, without removing the eye from the body of 

 the microscope. The stage is seven inches square. 

 The convenience of its being thus large is, that the 

 hands do not interfere with the object when adjust- 

 ing it. The heads that move the stage have their 

 axis in the same line, and so placed that with the 

 same hand the stage may be moved in all direc- 

 tions ; this is convenient when viewing an object, 

 the surface of which is very irregular ; with the 

 right hand you can move the stage, and there being 

 two beads to the adjustments for the body, with 

 the left the object can be adjusted into focus. There 

 are likewise two milled heads to one motion of the 

 stage, by which means both hands may be employed 

 at the same time, which is sometimes requisite. 

 On the same bar that the body rests, moves the 

 " achromatic condenser," by which arrangement it 

 is certain to move in the same line with the body, 



which we have ourselves been accustomed to 

 employ, and state what we regard as its advan- 

 tages; not omitting to notice the objections 

 which may be brought against it, and bearing 

 in mind that every microscopist is naturally 

 most partial to the form which he has himself 

 adapted to his own ideas of convenience. It 

 is principally constructed according to the 

 plans of Mr. Pritchard and Dr. Goring ; and 

 we may observe in liminc, that the objections 

 which have been brought against any form of 

 construction in which the body is screwed by 

 its lower extremity to a horizontal arm, as 

 placing it in the most unfavourable position for 

 vibration, independently of the stage, are ap- 

 plicable only to instruments which are not 

 made with sufficient solidity ; for, having had 

 an opportunity of comparing the quality in this 

 respect, of Mr. Ross's microscope, with our 

 own, the two being placed in exactly the same 

 circumstances, we could not find that there 

 was any inferiority on the part of the latter. 

 It must be borne in mind, that every increase 

 in the size and power of a microscope must be 

 accompanied by more than a corresponding 

 increase in solidity, in order to guard effec- 

 tually against oscillation. 



The stand or basement is a slab of solid 

 mahogany 12 inches square and 1^ inch thick, 

 loaded with lead at the corners, and having a 

 strip of thick baize, about 1J inch broad, glued 

 round the edge of the underside; the whole 

 weight bears upon the baize, which does not 

 readily communicate vibrations; and the large 

 surface over which the pressure is distributed 

 gives the instrument a degree of imperturba- 

 bility which would scarcely have been antici- 

 pated. The slab is surrounded by a slightly 

 elevated rim ; and it thus serves as a most con- 

 venient little table, on which the various pieces 

 of apparatus required for microscopical obser- 

 vation may be carried about witli the instru- 

 ment without any danger. The pillar of the 

 microscope carries at its lower extremity a 

 screw, above which is a flange or shoulder of 

 2 inches diameter; the screw is received into 

 a socket let into the wooden foot, and firmly 

 attached to it, and itself having a shoulder of 

 equal size ; so that, when the pillar is firmly 

 screwed down upon it, there is not the least 

 tendency to vibration between the two. The 

 socket is not let into the middle of the base, 

 however; but its centre is only 2$ inches from 

 one of the sides, and 9^, therefore, from the 

 other; so that, in fact, when the microscope is 

 placed vertically, the centre of the stage pretty 

 nearly corresponds with the centre of the foot. 

 The object of this is to give a decided prepon- 

 derance in weight to the front of the foot in all 

 positions of the microscope ; for we are inclined 

 to think that much of the oscillation so fre- 

 quently complained of in microscopes is to be 



which is most essential, for unless it did so whrn 

 using different power object-glasses, the axis of the 

 lenses would not coincide. There are m;iny other 

 conveniences and improvements to this microscope 

 which cannot be mentioned in this brief notice, 

 ED.] 



