using the common concave glasses till he was upwards of thirty years
of age, when No. 2 was barely sufiicient; and he very shortly had
recourse to No. 3. In the course of a few years an increase of the
defect rendered it necessary for him to employ glasses still deeper,
and his sight soon required No. 5, where it has remained stationary
to the present time. From the progress which Sir Charles Blagden
has observed in his own short-sightedness, he is of opinion that it
would have been accelerated by an earlier use of concave glasses, and
might have been retarded, or perhaps prevented altogether, by at—
tention to read and write with his book or paper as far distant as
might be from his eyes.
In this communication he takes the same opportunity of adding an experiment made many .years since on the subject of vision, with a View to decide how far the similarity of the images received by the two eyes contribute to the impression made on the mind, that they arise from only one object. In the house where he then resided, was a marble surface ornamented with fluting, in alternate ridgm and concavities. When his eyes were directed to these, at the distance of nine inches, they could be seen with perfect distinctness. When the optic axes were directed to a point at some distance behind, the ridges seen by one eye became confounded with the impression of concavities made upon the other, and occasioned the uneasy sensation usual in squinting. But when the eyes were directed to a point still more distant, the impression of one ridge on the right eye corresponded with that made with an adjacent ridge upon the left eye, 0 that the fiuting then appeared distinct and single as at first, but the object appeared at double its real distance, and apparently magnified in that proporfion. Though the different parts of the flutiug were of the same form, their colours were not exactly alike, and this occasioned some degree of confusion when attention was paid to this degree of dissimilarity.
A Method of drawing extremely/fine l/Vires. By William Hyde Wol: lastou, M1). Sec. R.S. Read February 18, 1813. [PhiL Trans. 1813, p. 114.]
The author refers to Musschenbroek for an instance of a gold wire, recorded to have been drawn by an artist at Augsburg so fine, that one grain of it would have the length of 500 feet. It is not said how this was effected, and some doubt has been entertained of the possi- bility of it; but the author of this paper shows how gold may be drawn to the same degree of fineness, and also that platina may be made with great facility much finer than is above described.
The general principle of the method is the same for both. The metal intended to be drawn is first reduced, in the common mode, to a wire of about Tenth of an inch in diameter; and it is then coated with silver, so as to form a rod of considerable thickness. The rod is then drawn, as usual, till it is reduced to a slender wire, and it is presumed that the gold or platina contained in it i reduced in the
