We have already shown in the article AC/IROMATIC TELESCOPE, that achromatic eye-pieces may be con structed with two, three, or four lenses, and therefore we have only to substitute one of these eye-pieces in place of the lenses of V and K, Fig. 27. Dr. Robison tried the eye-piece of Ramsrlen, described in the above article, (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 microscope, and found it to surpass every thing that he had seen. " The picture firmed by a solar microscope," says he, " is generally so indistinct, that it is fit only for amusing ladies, but with this magnifier it seemed perfectly sharp. We therefore recommend this to the artists as a valuable article of their trade." Another mode of improving the solar microscope has been described by Dr. Brewster, in his Treatise on New Philosophical Instruments, and is founded on the prin ciple already explained, (see p. 248.) as applicable to the compound microscopes.
The method of fitting tip the solar microscope, to render it susceptible of this improvement, is represented in Plate CCCLXXVII. Fig. 34. where AB is the illu minating 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 n, which has a tubular opening at E; and at the other end of the tube is cemented a circular piece of parallel glass m n. The tube m CD n 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 adjustment may be ef fected 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 image.
If the microscope is fitted up for the examination of transparent bodies, it is obvious, that the image will he 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 compl.:Aely removed,' and an ad ditional transparency is communicated by the fluid, which 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 transparency.
The advantages arising from immersion in a fluid, avhich have been very fully stated in Chapter II. p. 248, apply with peculiar force when the objects are used in the solar microscope. • This microscope may he rendered perfectly achro matic, by using the same fluids, and by giving the lens nearly the same radii of curvature, which have been al ready mentioned.
On the Lucernal Microscope.
THE lucernal microscope is an instrument for exhi biting to one or more persons magnified representations of microscopic objects when illuminated by an Argand lamp. It was invented by Mr. Adams, and has the pro perty of enabling the observer, who has no knowledge of drawing, to make an exact delineation of the object he is examining.
It is represented in Plate CCCLXXVII. Fig. 35, 36, 37, and 38. In Fig. 35. it is fitted up for viewing opaque objects, and consists of a large pyramidal box of ma hogany 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 cur ved piece IK. At N is a dove-tailed piece of brass for receiving the clove-tail at the end of the piece LAIN. The part MN consists of two brass tubes, one sliding within the other, and the inner one carries the flat piece of brass LAI, 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 AI, and it may be made to approach to or recede from the box, by pulling out or pushing in the tube NI to which it is attached. At the other end of the box is fixed a tube P, which receives another tube 0, at the end of which the magnifiers are fixed. A long square bar RS, which passes through the sockets YZ, carries the stagefg h i that holds the objects. This bar may be moved backwards or forwards, for the purpose 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 screw-nut shown separately in Fig. 36. The body of the microscope is kept steady by the brass bar d e, which sustains the curved piece KI.
The objects are placed in the front side of the stage f g h i between four small brass plates, the edges of two of which are seen at k and 1. 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 upper pieces of brass, are lifted up by the small nut in.