A writer in the _North-British Review_, No. 50, considers it strange
that a variety of facts which must have presented themselves to the
most careless observer should not have led to the earlier construction
of Optical Instruments. The ancients, doubtless, must have formed
metallic articles with concave surfaces, in which the observer could
not fail to see himself magnified; and if the radius of the concavity
exceeded twelve inches, twice the focal distance of his eye, he had in
his hands an extempore reflecting telescope of the Newtonian form, in
which the concave metal was the speculum, and his eye the eye-glass,
and which would magnify and bring near him the image of objects nearly
behind him. Through the spherical drops of water suspended before his
eye, an attentive observer might have seen magnified some minute body
placed accidentally in its anterior focus; and in the eyes of fishes
and quadrupeds which he used for his food, he might have seen, and
might have extracted, the beautiful lenses which they contain, and
which he could not fail to regard as the principal agents in the vision
of the animals to which they belonged. Curiosity might have prompted
him to look through these remarkable lenses or spheres; and had he
placed the lens of the smallest minnow, or that of the bird, the sheep,
or the ox, in or before a circular aperture, he would have produced a
microscope or microscopes of excellent quality and different magnifying
powers. No such observations seem, however, to have been made; and even
after the invention of glass, and its conversion into globular vessels,
through which, when filled with any fluid, objects are magnified, the
microscope remained undiscovered.