The Argand lamp, shown in Fig. 37. throws its light upon a glass hemisphere n, which conveys it to the con cave mirror o, from which it is reflected upon the ob jects.
When the stage for transparent objects, shown in Fig. 38. is to be used, the upper part f g r s, of the opaque stage is taken out, and the two legs 5 and 6 of the trans parent 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, and are adjusted by the nut 13, work ing in a rack 1, 2.
At the end AB of the wooden body, there is a slider represented as partly drawn out at A. When 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 shown in the fi gure, it is ready for adjustment. The lamp being placed before the glass hemisphere n, the mirror o must be in clined till it receives the light from the hemisphere, 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 LAI 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 an uniform field of light. The eye still looking through the aperture at L, the lenses are ad justed 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 ob jects, when magnified, are seen to the greatest advantage by a single observer, when his eye is applied to the aper ture L, but if two or three persons wish to see the ob jects at the same time, the guide LAI 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, 23 Ed. p. 84, Ste.
..lccount of a New Method of illuminating Objects in the Solar and the Lucernal Microscopes.
The great effects which still attach to the solar and lucernal microscopes, arise from the imperfect method of illuminatiag the objects. The method suggested by
Epinus, and employed almost universally by opticians, of reflecting the light concentrated by a lens upon the ob jects by means of a plane-mirror, is good enough so far as it goes ; but in consequence of the light arriving from one direction only, the surface of the illuminated object is covered with deep shadows ; and the intensity of illu mination 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. 25. or n, Fig. 35. The four cones, if condensed, arc then received before they reach their focus, by an inclined mir ror, such as ab, Fig. 25. or o, Fig. 35. which reflects them upon the object ef; the distance ab+bf being al ways less than the focal length of the illuminating lens NP. In the lucernal microscope, it would be adviseable 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 high degree of illumination would be obtained for very dark objects, or for high powers; and by shutting up one or more of the four lenses, or parts of them, we should be enabled to find the particular direction of the light which is best suited for developing the structure, which it is the object of the observer to discover.
On Microscofzic Objects.
Almost every object in nature may be considered as an object fit for the microscope, either as a whole, if it is small, or in its parts, if it has considerable magnitude. The name of microscopic objects, however, is generally given to those minute animals which cannot be seen without the microscope, or to particular structures in the animal, vegetable, and mineral kingdom, which are remarkable for their beauty when examined by the microscope.
In our article ANIMALCULE, we have already entered into great detail respecting the most interesting animals which have been discovered by the microscope, and have represented some of the most important in Plates XXIII. and XXIV. We shall therefore confine our sel% es at present to a brief enumeration of microscopic objects which possess a particular interest.