MICROSCOPE. 



229 



Martin'* 



tolir mi. 



Fij.30. 



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' Mi- microscope, which is used for shewing transparent ob- 

 PV jecta. The cylindrical tube 'i i the tube EF, 



Fig. 26, and m order to use it as a single microscope, 

 a handle c screws into a female screw at g, and the 

 tube Y is removed. The slider shewn in Fig. 28, and 

 containing six magnifiers, fits into a dovetail circle P, 

 Fig. 27- The slider at Fig. 29. slides in at k. Fig. 27. 

 and is used to condense the sun's rays strongly on the 

 object. Three of them marked 1, 2, 3, are used, cor- 

 responding to the numbers in Fig. 28. 



The body of the solar microscope is shewn at 

 ABCDEF, the part A BCD being conical, and the part 

 CDEF cylindrical. This but part receives the tube G 

 of the opaque object box. A large concave lens is 

 placed at AB for receiving the rays from the mirror 

 ONP, and converging them into the box HILX. 



A brass frame NOP is fixed to the moveable circular 

 plate a b e, and carries a plane mirror for reflecting the 

 sun's light upon the convex glass at AB; and by means 

 of rackwork moved by the nuts Q and R, this mirror 

 can be turned into such a position with respect to the 

 incident ray, that the reflected ray passes along the 

 axis of the tubes. The microscope is fattened to a 

 window-shutter by two screws d, e. The box HILX 

 for opaque objects is shewn open. It contains a plane 

 mirror M for reflecting the light from the lens A B up- 

 on the object, and this mirror is adjusted through the 

 door k i to the proper angle by a screw S. Two tubes 

 of brass are shewn at V and K, one sliding within the 

 other, and the outer one V sliding into the box. These 

 tubes carry two magnifying lenses. The interior tube is 

 sometimes taken out, and the exterior one (which is 

 seen within the box ) is then used alone. 



A brass plate H has its back part fixed to a tube A 

 by means of a spiral wire within the tube, which al- 

 ways presses the plate against the side H of the box. 

 The sliders, with the opaque objects shewn in Fig. 30. 

 pass between this plate and the side of the box, which 

 is done by drawing out the plate H by means of the 

 nut g. The following are the other parts of the opaque 

 solar microscope. 



Fig. 32. is a brass quadrangular slider case, to hold 

 any animal or opaque object, which u to be placed at 

 H, like the other tliders. 



Fig. 33. is a fourglas* slider in a brass frame, for ani- 

 malnilsr, dec. which U to be placed between the plates 

 at w, Fig. 27. 



Before using the solar microscope, a circle a little 

 larger than a be, must be made in the shutter of a 

 window opposite to the sun. The mirror NOP U then 

 put through this hole, and the square plate applied to 

 the shutter. The places corresponding to the two holes 

 of the screws d, e, are then marked on the shutter with 

 a pencil, and boles made large enough to admit the 

 screws, which, passing through the shutter, are screwed 

 into their respective hole* in the square plate, so M to 

 hold the microscope firmly in its position. 



In order to use the microscope for opaque objects, 

 the mirror NOP is turned by the screws Q, R, one of 

 which gives it a circular motion, and the other raises or 

 depresses it, till it reflects the sun's rays through the 

 tube ABEF upon a white paper screen or cloth from 

 4 to 8 feet square, placed at a distance of from 5 to 

 8 feet from the window. The tube G of the box 

 HILX is then put into the tube EF, and the mirror 

 M is adjusted through the door k i till the objects are 

 strongly illuminated. The door k i being shut, a distinct 

 image of the object will be obtained upon the screen, by 

 adjusting the tubes V and K with the magnifiers, which 



is done by moving them backwards and forwards. As 

 the sun is always in motion, it is necessary to shift the 

 place of the mirror NOP, so as to keep the reflected 

 light coincident with the axis of the tube. This effect 

 may be produced in a superior manner by adapting the 

 solar microscope to a HELIOSTATE (see that article in 

 vol. X. p. 705.) or piece of clockwork, which drives 

 the mirror continually so as to make it always reflect 

 the sun's light in one direction. 



In order to use the microscope for transparent ob- 

 jects, take away the opaque box HlLX, and insert the 

 tube Y of Fig. 27. in EF. Place the slider, Fig. 28. in 

 its place at n, a condenser, Fig. 29. into the opening at 

 h, and the slider, Fig. 32. with the objects between the 

 plates at m: then having adjusted the mirror NOP as 

 before, a magnificent picture of the object will be seen 

 on the white screen. 



The solar microscope now described, though possess- 

 ing all the advantages that can arise from mechanical 

 construction, il still a very imperfect instrument, being 

 liable to all the bad effects arising from the different re- 

 frangibilitv of light. 



The only method of remedying this defect, is to cor- 

 rect the colour either by using a combination of lenses 

 for the purpose of forming the image, or to use a lens 

 composed of differently dispersing and refracting media. 



We have already shewn in the article ACHROMATIC 

 TELESCOPE, oL i. p. 109- that achromatic eye-pieces 

 may be constructed with two, three, or four lenses, and 

 therefore we have only to substitute one of these eve- 

 pieces in place of the lenses of V and K, Fig. 27. Dr. 

 Robison tried the eye-piece of Ramsden, described in 

 the above article, p. 109, bottom of column 2. (where, 

 by the way, one of the focal lengths is stated at 7.025 

 in place of 1.025) as the magnifier of a solar micro- 

 scope, and found it to surpass every thing that he had 

 seen. " The picture formed by a solar microscope/' 

 says he, " is generally so indistinct, tint it is fit only for 

 amusing ladies, but with this magnifier it seemed per- 

 fectly sharp. \Ve therefore recommend this to the artNt< 

 as a valuable article of their trade." 



Another mode of improving the solar microscope has 

 been described by Dr. Brewster, in his Treatiie on 

 Nfif PhilotopMcal fntirummlj, and is founded on the 

 principle already explained, (see p. 226.) as applicable 

 to the compound microscopes. 



The method of fitting up the solar microscope, to 

 render it susceptible of this improvement, is repre- 

 unttd in Fig. 34. where AB is the illuminating 

 lens which receives the parallel rays of the sun, and 

 throws them upon the object. The object lens CD is 

 firmly cemented into one end of a tube m CD >i, which 

 has a tubular opening at E ; and at the other end of 

 the tube is cemented a circular piece of parallel glass 

 mm. The tube mCDn is then filled with water, or 

 any other fluid ; and the object, when fixed upon a 

 slider, or held with a pair of forceps, is introduced into 

 the fluid at the opening E. The slider, or the forceps, 

 may be easily rendered moveable, so that the object 

 may be placed at a proper distance from B ; or the ad- 

 justment may be effected by a motion of the screen on 

 which the image is projected. The plate of glass m n 

 might be removed, and the whole of the space between 

 AB and CD filled with fluid ; but if the fluid had any 

 tinge of colour, the transmitted light would, in this 

 case, partake of it, and injure the distinctness of the 



Solar Mi- 

 croscopes. 



Method of 

 using it for 

 transpa- 



rent o!) " 



eyepiece, 

 recom- 

 mended bjr 



Dr - Hobu 



Improve- 

 raent on 

 the tolir 

 microwope 



Fil 



If the microscope is fitted up for the examination of 

 transparent bodies, it is obvious, that the image will be 



