The micrometers are constructed with moveable frames or tubes, so as to be either applied or taken away in the readiest manner.
For the uses of the pearl micrometer as applied to the telescope, see Mr. Cavallo’s pamphlet descriptive of its use, 8vo. 1793, and the Philosophical Transactions for 1791.
A DESCRIPTION OF THE MOST APPROVED MICROSCOPES, AND THE METHOD OF USING THEM.
In the preceding chapter I have endeavoured to give a comprehensive view of the theory of the microscope, and the principles on which the wonderful effects of this instrument depend. I shall now proceed to describe the various instruments themselves, their apparatus, and the most easy and ready mode of applying them to use; selecting for description those that, from some peculiar advantage in their construction, or from the reputation of the authors who have recommended and used them, are in most general use. What is said of these will, I hope, be sufficient to enable the reader to manage any other kind that may fall in his way.
DESCRIPTION OF ADAMS’S IMPROVED AND UNIVERSAL LUCERNAL MICROSCOPE. Fig. 1. Plate III.
This microscope was originally thought of, and in part executed by my father; I have, however, so improved and altered it, both in construction and form, as to render it altogether a different instrument. The approbation it has received from the most experienced microscopic observers, as well as the great demand I have had for them, has fully repaid my pains and expenses, in bringing it to its present state of perfection.
As the far greater part of the objects which surround us are opake, and very few sufficiently transparent to be examined by the common microscopes, an instrument that could be readily applied to the examination of opake objects, has always been a desideratum. Even in the examination of transparent objects, many of the fine and more curious portions are lost, and drowned as it were in the light which must be transmitted through them; while different parts of the same object appear only as dark lines or spots, because they are so opake, as not to permit any light to pass through them. These difficulties, as well as many more, are obviated in the lucernal microscope; by which opake objects of various sizes may be seen with ease and distinctness; the beautiful colours with which most of them are adorned, are rendered more brilliant, without in the least changing their natural teints. The concave and convex parts of an object retain also their proper form.