4-55 



using the common concave glasses till he was upwards of thirty years 

 of age, when No. 2 was barely sufficient ; 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 ridges 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, so that the 

 fluting then appeared distinct and single as at first, but the object 

 appeared at double its real distance, and apparently magnified in that 

 proportion. Though the different parts of the fluting 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 Wires. By William Hyde Wol- 

 laston, M.D. Sec. R.S. Read February 18, 1813. [Phil. Trans. 

 1813,^. 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 T -o-oth 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 is reduced in the 



