1878.] 



The Magic Mirror of Japan. 



141 



the light best, and if the screen is distant, may be employed to pro- 

 duce a large figure of the pattern on the back of the mirror, but the 

 result is not nearly as beautiful as that obtained by either of the 

 former three methods, the first two in particular of which, if the 

 mirror is placed in a darkened room, at about fourteen feet distance 

 from the luminous point produced by a tropical sun, cause the reflec- 

 tion on the wall to assume an appearance startling even to an educated 

 mind, and which might well have brought to the feet of the magician 

 the ignorant poor of the middle ages. 



Referring to the arrangement of mirror and lens shown in fig. 4, 

 and remembering the reasoning employed in the case of figs. 1, 2, and 

 3, we should conclude that if a portion, AB, of the mirror is more- 

 concave than the rest, this portion ought to appear as bright on a 

 dark ground if the screen be held in the positions 1, 2, or 4, since, in 

 all these, DE is less than CD or EF, but if it be held at any point, 3 

 in the region between the principal focus P and JJ, then, since here 

 DE is greater than CD or EF, the concave portion ought to appear as 

 dark on a relatively light ground, while at JJ, the image being 

 uniformly illuminated, the appearance of the pattern ought to dis- 

 appear altogether. We should expect, then, that the passage of the 

 screen, either through P or through JJ, ought to produce an inversion 

 of the phenomenon if the theory that we are here advocating of the 

 Japanese mirror be correct. 



Fig. 5. 



Again, imagine the lens LL to gradually move up to the mirror 

 until it attains a very near position, as in fig. 5, then an inspection of 

 the direction of the rays shows that any concave part, AB, of the 

 mirror must appear on the screen as light on a dark ground for all 

 points between the lens and the principal focus P, but that it will be^ 

 seen as dark on a relatively light ground for all positions of the screen 



