166 Miscellanies. 



the weight the blade gives, till the object is attained. If the razor 

 have been properly ground and prepared, a very fine edge will be 

 given in a few seconds, and it may be renewed again during a very 

 long period, wholly by the same means. 



The author has had a razor in constant use during more than two 

 years and a half, and no visible portion of its metal has been worn 

 away, though the edge has remained as fine as possible, and he has 

 never at any one time spent a quarter of a minute in setting it. He 

 thinks it operates best when the temperature of the blade has been 

 raised by the aid of warm water. 



Although a cylindrical bar is much superior to a plane surface for 

 for giving an edge to a razor or pen knife, it is ill calculated to give a 

 fine point to a lancet. For this purpose a plane surface is made a 

 quarter of an inch wide on one side of the bar, and this form is found 

 to be extensively useful. 



The author finds that the material which appeared to receive the 

 most eager edge (and very durable) was wootz, and that which re- 

 ceived the smoothest edge and best adapted to surgical purposes, was 

 a"mixture of rhodium and steel ; the powers of pure steel appeared 

 to be intermediate. — Journal of the Royal Institution, Vol. I, p. 13. 



3. Interesting optical experiments. — If, without closing the lids, 

 the left eye be covered with the hand, or some other obstacle, and a 

 candle or lamp be held in the right hand within two or three inches 

 of the right eye but rather below it, (keeping the eye directed straight 

 forward,) on moving the candle slowly backward and forward, i. e. 

 from right to left, (or if the candle be held on the right side of the 

 eye it may be moved up and down,) a spectrum appears after a short 

 time in which the blood vessels of the retiiia, with all their ramifica- 

 tions, are distinctly seen projected, as it were, on a plane without the 

 eye, and greatly magnified. They seem to proceed from the optic 

 nerve, and consist of two upper and two lower principal branches, 

 which are variously ramified towards the field of vision, where a dark 

 point is seen, which sometimes appears concave. A similar but in- 

 verted figure, and less distinct, appears in the left eye. The origin 

 of the vessels is a dark oval spot, with a light areola ; the figure it- 

 self, or rather fragments of it, are seen under various other circum- 

 stances. There can be no doubt that it is formed by the central ves- 

 sels of the retina. A remarkable circumstance of this phenomenon 

 is, that at the point corresponding to the projection of the foramen 



