[15] Memoires sur les Differences de la Construction et des Effets du Microscope, de M. L. F. Dellebarre, 1777.
From this period, to the year 1736, the microscope appears not to have received any considerable alteration, but the science itself to have been at a stand. The improvements which were making in the reflecting telescope, naturally led those who had considered the subject, to expect a similar advantage would accrue to microscopes on the same principles: accordingly we find two plans of this kind; the first was that of Dr. Robert Barker. This instrument is entirely the same as the reflecting telescope, excepting the distance of the two speculums, which is lengthened, in order to adapt it to those pencils of rays which enter the telescope diverging; whereas, from very distant objects, they come in a direction nearly parallel. But this was soon laid aside, not only as it was more difficult to manage, but also because it was unfit for any but very small or transparent objects: for the object being between the speculum and the image, would, if it were large and opake, prevent a due reflection of light on the object.
The second was contrived by Dr. Smith.[16] In this there were two reflecting mirrors, one concave and the other convex; the image was viewed by a lens. This microscope, though far from being executed in the best manner, performed, says Dr. Smith, very well, so that he did not doubt but that it would have excelled others, if it had been properly finished.
As some years are more favourable to the fruits of the earth, so also some periods are more favourable to particular sciences, being rich in discovery, and cultivated with ardor. Thus, in the year 1738, Dr. Lieberkühn’s invention of the solar microscope was communicated to the public: the vast magnifying power which was obtained by this instrument, the colossal grandeur with which it exhibited the minima of nature, the pleasure which arose from being able to display the same object to a number of observers at the same time, by affording a new source of rational amusement, increased the number of microscopic observers, who were further stimulated to the same pursuits by Mr. Trembley’s famous discovery of the polype: the wonderful properties of this little animal, together with the works of Mr. Trembley, Baker, and my father, revived the reputation of this instrument.[17]