230 



M I C R O S C O P E. 



cope. 



much more perfect than if it had been formed in the 

 common way. The opacity which arises from a con- 

 traction of parts is thus completely removed, and sn 

 additional transparency is communicated by the fluid, 

 vhich could not have been obtained in any other way. 

 Substances, indeed, which with the common solar mi- 

 croscope appear opaque, will, in the present form of 

 the instrument, exhibit a very great degree of transpa- 

 rency. The advantages arising from immersion in a 

 fluid, which have been very fully stated in Chapter 

 II. p. 226., apply with peculiar force when the ob- 

 jects are used in the solar microscope. 



This microscope may be rendered perfectly achro- 

 matic, by using the same fluids, and by giving the lens 

 nearly the same radii of curvature, which have been 

 already mentioned. 



CHAP. IV. 



On the Lucernal Microscope. 



On the Iu. THE lucernal microscope is an instrument for exhi- 

 eernal mi- biting to one or more persons magnified representations 

 croscope. o f microscopic objects when illuminated by an Argand 

 PLATE lamp. It was invented by Mr. Adams, and has the 

 CCCLXXIX. property of enabling the observer, who has no know- 

 ledge of drawing, to make an exact delineation of the 

 object he is examining. 



It is represented in Fig. 35, 36, 37, and 38. In Fig. 

 Fig. 35, 36, 35, it is fitted up for viewing opaque objects, and con- 

 37, 38. s j g ts of a large pyramidal box of mahogany ABCDE, 

 about 14 inches long, and six inches square at its large 

 end. This box is supported on a brass pillar FG, by 

 means of the socket H, and the curved piece IK. At N 

 is a dove-tailed piece of brass for receiving the dove- 

 tail at the end of the piece LMN. The part MN con- 

 sists of two brass tubes, one sliding within the other, 

 and the inner one carries the flat piece of brass LM, at 

 the top of which is a hole L for the eye. This piece may 

 be raised or depressed, and fixed in any position by a 

 milled screw at M, and it may be made to approach to 

 or recede from the box, by pulling out or pushing in 

 the tube M to which it is attached. At the other end of 

 the box is fixed a tube P, which receives another tube 

 O, at the end of which the magnifiers are fixed. A 

 long square bar RS, which passes through the sockets 

 YZ, carries the stage/ h i that holds^the objects. This 

 bar may be moved backwards or forwards, for the pur- 

 pose of adjusting the stage, by means of a pinion at a 

 working in a rack ; and this pinion is moved either by 

 a handle b c furnished with an universal joint, or by the 

 Fig. 36. screw-nut shewn separately in Fig. 36. The body of 

 the microscope is kept steady by the brass bar de, which 

 sustains the curved piece KI. 



The objects are placed in the front side of the stage 

 fg h i, between four small brass plates, the edges of two 

 df which are seen at k and /. The two upper pieces of 

 brass which are moveable, are fixed to a plate which 

 is acted on by a spiral spring, that presses them down 

 and confines the slider. This plate, and the two up- 

 per pieces of brass, are lifted up by the small nut in. 

 Fig. 37. The Argand lamp, shewn in Fig. 37. throws its 

 light upon a glass hemisphere a, which conveys it to 

 the concave mirror o, from which it is reflected upon 

 the objects. 



When the stage for transparent objects, shewn in 



'8- 38 - pjg. gg. is to be used, the upper part fg rs, of the 



opaque stage is taken out, and the two legs 5 and 6 of 



the transparent stage fit into the under part r s. The 

 sliders are confined at 7, and the lenses for condensing 

 the light are placed in the brass tubes 9, 10, which 

 may be drawn out or pushed in by the pin 11. The 

 magnifiers are screwed into the hole 12, ond are ad- 

 justed by the nut 13, working in a rack 1, <>.. 



At the end AB of the wooden body, there is a slider 

 represented as partly drawn out at A. \Vhen it is 

 taken completely out, three grooves will be seen, one 

 of which contains a board forming the end of the box, 

 the next a frame with a ground glass, and the third, 

 ( or that farthest from AB, ) two large convex 

 lenses. 



When the instrument is fitted up as shewn in the 

 figure, it is ready for adjustment. The lamp being 

 placed before the glass hemisphere n, the mirror o must 

 be inclined till it receives the light from the hemis- 

 phere, and reflects it upon the objects. The wooden 

 slide A being taken out, and the cover and the ground 

 glass removed from their respective grooves, the piece 

 LM is pulled out or pushed in, and raised or depressed 

 till the eye at L sees the large lens placed at the end 

 AB of the wooden body, filled by a uniform field of 

 light. The eye still looking through the aperture at 

 L, the lenses are adjusted to their focal distance by 

 turning the pinion A, and the ground glass is placed 

 before the large lenses. The image of the objects will 

 now be seen beautifully depicted upon the ground 

 glass, and may be accurately delineated upon it with 

 the point of a pencil. The objects when magnified, 

 are seen to the greatest advantage by a single observer, 

 when his eye is applied to the aperture L, but if two or 

 three persons wish to see the objects at the same time, 

 the guide LM must be removed. The large lens must 

 be taken out of the groove, and the image received on 

 the rough glass. 



Some slight improvements have been made on the 

 Lucernal microscope by opticians, and by the Rev. Dr. 

 Prince and Mr. Hill, an account of which will be found 

 in Adam's Essays on the Microscope, 2d Ed. p. 84, &c. 



Account of a New Method of Illuminating Objects in 

 the Solar and the Lucernal Microscopes. 



The great defects which still attach to the solar and Account of 

 lucernal microscopes, arise from the imperfect method a " ew e - 

 of illuminating the objects. The method suggested by ! ho< ! c 

 jEpinus, and employed almost universally by opticians, ob',,""''^ 

 of reflecting the light concentrated by a lens upon the the solar 

 objects by means of a plane-mirror, is good enough so and the lu. 

 far as it goes ; but in consequence of the light arriving cernal mi- 

 from one direction only, the surface of the illuminated croscopc. 

 object is covered with deep shadows ; and the intensity 

 of illumination is by no means sufficient when the power 

 of the instrument is considerable. 



We propose, therefore, that in the solar microscope 

 the sun's light should be reflected by a very large mir- 

 ror through four apertures, A, B, C, D, each of which 

 is furnished with an illuminating lens, such as NP, Fig. 39. 

 Fig. 25, or n, Fig. 35. The four cones, if condensed, 

 are then received before they reach their focus, by an 

 inclined mirror, such as alt, Fig. 25, or o, Fig. 35, 

 which reflects them upon the object ef; the distance 

 ab + bf being always less than the focal length of the 

 illuminating lens NP. In the lucernal microscope, it 

 would be advisable to place an argand lamp opposite 

 each of the apertures A, B, C, D. By these means the 

 light would fall upon the surface of the object in four 

 different directions ; a high degree of illumination 



