224 



MICROSCOPE. 



scopes. 



Fig. 20. 



Compound click the instant that any of the magnifiers comes into 

 Micro- i ts exact position in the axis of the other lenses. The 

 lenses are numbered from one to six, and the proper 

 number appears in a small opening made in the upper 

 side of the box P. This box screws into the arm CD, 

 and may be taken off when required. If we unscrew 

 the body Al>, the instrument becomes a single micro- 

 scope by looking directly through any of the lenses in 

 the wheel. The mirror O may be moved up or down 

 the bar EF, by pushing against the screw at r. In ad- 

 dition to the apparatus already described, as belonging 

 to single microscopes and to Cuff's compound micro- 

 scope, the following may be enumerated. A moveable 

 stage W, which is applied to the hole S of the stage by 

 the pin a, and has thus a horizontal motion under the 

 field of view. A very deep concave lens r is fitted to 

 the large hole of this stage, and also the concave and 

 plane glasses s and o, while to the small holes x, x a 

 black and white piece of ivory iv is fitted for opaque ob- 

 jects, and a concave and plane glass similar to o and s. 

 The arm CD is sometimes furnished with rack work, 

 to turn the pinion above, so as to move the magnifiers 

 in the most accurate manner over the objects ; and the 

 stage NIS is sometimes jointed, in order to turn by a 

 screw and teeth in a horizontal direction. In using 

 this microscope, the slider holder K, containing a slider 

 of objects, is placed in the stage NIS, and the arm CD 

 is moved in its socket, till a mark on the side is brought 

 to the edge of the socket. The arm is then turned, till 

 the magnifier is directly over the object, the eye being 

 then placed at the upper end of the tube AB, and the 

 light reflected strongly up into it from the mirror O. 

 The pinion M is then turned to the right or left till 

 the object is seen in the most distinct manner. When 

 the objects are opaque, the slider-holder K is removed, 

 and either the concave glass, or the jointed pliers, are 

 placed on the stage. The concave silver speculum e is 

 then screwed into the arm a, which is placed on the stage, 

 with the cylindrical part passing through the hole I ; 

 and the light being reflected upon the speculum from 

 the mirror O, it will be strongly condensed by it, and 

 thrown upon the opaque object. 



Improve- ^ we consider the construction of the different com- 

 ment on pound microscopes which have been described, it will 

 the com- be obvious, that a great deal must depend on the accu- 

 pound mi- rac y w ith which the axes of the small magnifying 

 croscope. j enses coincide with the axis of the instrument, or that 

 of the eye-glasses. The difficulty of effecting such a 

 coincidence is very great, and we believe is in a great 

 measure overlooked. We conceive, therefore, that the 

 tube which holds the magnifying lenses should have 

 an universal motion, so that, by means of screws, the 

 axis of the lenses could be brought into perfect coin- 

 dencc with the axis of the eye-glasses. 



III. Amici' t Reflecting Microscope. 



Amici'a re- ^ e nave a l rea dy seen that the reflecting microscope 

 fleeting mi- of D r - Barker was nothing more than the Gregorian 

 cioscope. telescope, with its tube lengthened so as to permit it 

 to act as a microscope ; and that the reflecting micro- 

 scope of Dr. Smith was the Cassegrainian telescope 

 fitted up in a similar manner. The new reflecting mi- 

 croscope constructed by Professor Amici of Modena, and 

 with which he has made several important discoveries, 

 is in like manner the Newtonian telescope converted 

 into a microscope. 



It consists of a horizontal brass tube ABCD, 12 Compound 

 inches long, and 1 T J of an inch in diameter. A con- Micro- 

 cave metallic speculum AB, having its reflecting surface 

 a portion of an ellipsoid, whose foci are F and f, is 

 placed at one end of the tube; the distance AF being 

 2, S jy inches, and A/ 12 inches. A small arm rx within Fig. 21. 

 the tube, carries a plane speculum of an oval form, 

 placed at the distance of 1^- inches from AB, sup- 

 ported by an oblique section of an metallic cylinder, -/^ of 

 an inch in diameter, and inclined 45 to the axis F/l 

 The object is placed below the tube at MN, and as tar 

 before the mirror s as the focus F of AB is behind it ; 

 and it is supported by a moveable object-bearer attached 

 to the pillar below it. The diameter of the tube ABCD 

 is about IVo inches, and the thickness of its metal ^th. 

 The object is always placed at the distance of half an 

 inch from the edge of the tube, and may therefore 

 be illuminated by a convex lens, attached in the usual 

 way to the stage or object-bearer. A large concave 

 illuminating mirror below for throwing light upon 

 transparent objects, has a diameter of about 3 inches, 

 and a focal length of about 2 Y ! j. M. Amici has been 

 able to apply to this instrument, a power of one mil- 

 lion*, calculating the number of times that the superficies 

 is magnified, whereas the best microscopes of Adams, 

 Dollond, Delebarre, do not magnify more than 225,000, 

 or about 4-75 times in diameter. See The Edinburgh 

 Philosophical Journal, Vol. i. p. 135, where a more 

 detailed account of this instrument will be found. 



IV. Dr. JBretvster's Reflecting Microscope. 



This instrument, which will be understood from 0r. Brew- 

 Fig. 22, possesses several advantages, and in particu- ster's ve- 

 lar that of being applicable to the stand and apparatus of Besting ml- 

 any compound microscope. Though it is drawn in a C1 'scope. 

 horizontal position, it is intended to be placed vertical- *>' 

 ly. It consists of a concave speculum AB, whose sur- 

 face is a portion of an ellipsoid, having F and J for its 

 foci. It is perforated at O, like the speculum of a Gre- 

 gorian telescope ; and between this aperture ami F is 

 placed a small convex speculum s, whose surface is 

 part of an ellipsoid, having F and <p for its foci ; s f be- 

 ing equal to MN, the distance of the object. The 

 back of the speculum is ground into a concave form a b, 

 for the purpose of condensing the light upon the ob- 

 ject MN. The rays diverging from MN are made to 

 diverge still more by reflection from the small mirror 

 s, so that F is their virtual focus ; and these reflected 

 rays, falling upon the speculum AB, as if they had di- 

 verged from one of its foci F, will be reflected to f; 

 and there form a magnified image, which will be again 

 magnified by the eye-glass placed at LL. The convex 

 mirror s is carried by the arm * r, which is moved by 

 means of the screw r T, so that F is one of its foci. 

 An object placed at MN will therefore be seen very 

 distinctly by a microscope of this kind ; and it has 

 such a distance from the mirror AB, as to be capable 

 of receiving any degree of artificial illumination. If 

 this microscope is placed vertically in the arm ED of 

 the compound microscope shown in Fig. 19, made 

 large enough to receive it, it may be used along with 

 all the apparatus adapted to that or to any other com- 

 pound microscope. If a change of magnifying power 

 is required, we have only to use a deeper eye-glass 

 LL ; and as the place of the object is not altered by 

 this change, the concave illuminating speculum a 6 



This is 1000 times reckoned i& the usual way. 



