CATADIOPTRICAL PHANTASMAGORIA. 87 



variations in the size of the phantasms, and the 

 transformations of one figure into another. The 

 contrivance for adjusting the lens LL, to give a 

 distinct picture at different distances of the screen, 

 will, of course, be required in the present appa- 

 ratus. In order to give full effect to the phan- 

 tasms, the living objects at AB will require to be 

 illuminated in the strongest manner, and should 

 always be dressed either in white or in very 

 luminous colours; and, in order to give them 

 relief, a black cloth should be stretched at some 

 distance behind them. Many interesting effects 

 might also be produced by introducing at AB 

 fine paintings and busts. 



It would lead us into too wide a field were we 

 to detail the immense variety of resources which 

 the science of optics furnishes for such exhibi- 

 tions. One of these, however, is too useful to be 

 passed without notice. If we interpose a prism 

 with a small refracting angle between the image 

 ab, Fig. 7, and the lens LL, the part of the 

 figure immediately opposite to the prism will be 

 as it were detached from the figure, and will be 

 exhibited separately on the screen P Q. Let us 

 suppose that this part is the head of the figure. 

 It may be detached vertically, or lifted from the 

 body as if it were cut off, or it may be detached 

 downwards and placed on the breast as if the 

 figure were deformed. In detaching the head 

 vertically or laterally, an opaque screen must be 

 applied to prevent any part of the head from be- 

 ing seen by rays which do not pass through the 

 prism ; but this and other practical details will 

 soon occur to those who put the method to an 

 experimental trial. The application of the prism 



