The solar microscope has been so nearly superseded by the oxy-hydrogen, that a brief description of the latter must suffice, particularly as their optical principles are similar.
The primary object in both is to throw an intense light upon the object, which is sometimes done by mirrors, and sometimes by lenses.
In Fig. 30, L represents the cylinder of burning lime, R R the reflector, which concentrates the light upon the object O O; the rays from which, pa.s.sing through the two plano-convex lenses, are brought to foci upon a screen placed at a great distance, and upon which is formed the magnified image.
[Ill.u.s.tration: Fig. 30.]
Fig. 31 shows a combination of lenses to condense the light upon the object. In either case the optical arrangements by which the image is formed admit of the same perfection as those which have been described for the compound microscopes. A few achromatic gla.s.ses for oxy-hydrogen microscopes have been made, and they will ultimately become valuable instruments for ill.u.s.trating lectures on natural history and physiology. One made by Mr. Ross was exhibited a few months since at the Society of Arts to ill.u.s.trate a lecture on the physiology of woods. It should be observed, however, that the oxy-hydrogen or solar microscope requires either a spherical screen, or that the objects should be mounted between spherical gla.s.ses, in order to bring the whole into focus at one time. This latter plan was adopted on the occasion just mentioned with perfect success.
[Ill.u.s.tration: Fig. 31.]