4 T HORV, /a/>anese ''Magic" Mirrors. 



reveal some peculiarities, and this proved to be the case. 

 By making the mirror more or less convex by hand 

 pressure, although only in one direction, the design in the 

 one case started out in a wonderfully vivid manner, and 

 in the other a blurring was the result. It was now only 

 the work of an hour or so to have an arrangement fitted 

 to the back of the mirror, whereby more or less pressure 

 could be brought to bear on it, and with this the effects 

 produced were very pronounced. 



In order to absolutely determine whether, after all, 

 some of the effect produced may not be due to the 

 varying density of the metal, the back of another mirror 

 casting was thickly coated with resin so as to prevent any 

 flexure whatever during grinding and polishing — the 

 polishing in this case also, to make assurance doubly sure, 

 being done by the hand alone, no polishing block being 

 used. The effect produced was that only the faintest 

 indication of the design appeared on reflection, until the 

 mirror was strained, when it became lighter or darker than 

 the surrounding surface according as the reflecting surface 

 was more or less convex than in the normal state. 



On soldering an arrangement to the back in order to 

 show the effects, a slight strain was put upon the mirror, 

 rendering it more convex, and thus a decided effect was 

 produced which did not exist when the edge of the 

 mirror was free. A curious fact is brought out by means 

 of this arrangement, but one quite to be expected, viz., 

 that, when the surface is rendered less convex than the 

 normal condition, the principal features at all events 

 appear dark with a bright border. This, again, can easily 

 be shown to be the result of unequal flexure. 



A third mirror casting was next fitted with a chamber 

 from which the air was partially exhausted. On grinding 

 and polishing the mirror whilst in this condition of flexure, 



