from its Face the Figures embossed upon its Bade. 43i^ 



sent to England, either to Sir John Herschel, or to the writer . 

 of this notice ; and in the mean time he proposes to us the 

 question, " How are these strange optical effects produced?" 

 Mr. Swinton himself ingeniously conjectures that the phe- 

 nomena may have their origin in a difference of density in 

 different parts of the metal, occasioned by the stamping of the 

 figures on the back, the light being reflected more or less 

 strono-jy from parts that have been more or less compressed. 

 If mentals were absolutely opaque, and if the light which they 

 reflect never entered their substance, as in the case of re- 

 flexions from transparent bodies, then the only possible way 

 by which they could give a picture of the figures stamped be- 

 hind would be that which Mr. Swinton suggests *. 



I believe, however, on the authority of tlie phaenomena of 

 elliptical polarization, that in silver nearly one half of the 

 reflected light has entered the metal, and in other metals a 

 less portion; so that we may consider the surface of every 

 metal as transparent to a certain depth,— a fact which is proved 

 also by the transparency of gold and silver leaf. Now this thin 

 film having its parts of variable density in consequence of 

 the stamping of the figure, might reproduce the figure by re^ 

 flexion. It is well ki\o\yi\ X.hi\t sWvev polished bi/ Jiammering, 

 acts differently upon light from silver that has received a spe- 

 cular polish ; and I have elsewheref expressed the opinion 

 that a parabolic reflector of silvered copper polished by ham- 

 mering, will, from the difference of density of different parts 

 of the reflecting film, produce at the distance of many miles 

 a perceptible scattering of the reflected rays similar to what 

 takes place in a transparent fluid or solid, or gaseous medium. 

 I am satisfied, however, that, at the distance of a few inches 

 from the Chinese mirror, this evanescent effect will be alto- 

 gether imperce})tible, and that we must seek for another cause 

 of the phaMiomenon under consideration. 



Some years ago I had occasion to observe the light of the 

 sun reflected upon paper from a new and highly-polished gilt 

 button, and I made u drawing at the time of the figure which 

 appeared in the spectrum. It consisted of radiations exactly 

 like the spokes of a carriage-wheel, the radiations being 52.t7f«t 



• A series of very pretty deceptions miglu be niaile on the same principle, 

 by painting' (with thin trunspnreiit vurnishes laid <m in narrow lines) a 

 figure on the back surface of a plate of glass. The fujnrc would be seen by 

 reflecting the light of the sun upon a wall, in consequence of the reflexion 

 being destroyed, or nearly so, at those parts of the hack surface which are 

 covered with the varnish, and of the light being scattered at the outer sur- 

 face of the varnish. In ordinary lights the lines would not he visible, but 

 they would distinctly appear in the reflected ra}s of the suu. 



t Edinb. Trans, vol. xi. p; 47. 



