the Permanence of Impressions on the Retina. 535 



knit, and its eyes are directed toward the lire ; at the same time 

 the fire kindles, flames up, and casts a bright light, which strongly 

 illumines the head beneath, and causes the parts of the latter 

 M'hich remain in shade to appear very dark. When at length 

 the head rises and takes breath, its cheeks flatten, its mouth 

 opens, its brows grow smooth, and its eyes are directed towards 

 the spectator ; the fire also then becomes less glowing, loses 

 some of its brightness, and the head, which moreover is less 

 near to it, is seen in semi-darkness. One of our great artists, 

 M. Madou, has been kind enough, at my request, to di-aw the 

 model of the head taken at the moment when it blows with the 

 greatest force. I aftei-wards placed this drawing in one of the 

 compartments of the disc, increasing the angular dimensions of 

 all its pai'ts in the relation of 4 to 5 ; I then modified it suitably 

 in the other compartments, and paid the greatest attention to 

 the execution of these figm'es. The ordinary phenakisticope 

 gives but a very imperfect idea of the efi'ects which may be pro- 

 duced by the emplojTnent of the principle on which it is founded, 

 effects which are completely realized by means of the new appa- 

 ratus now described : my little blowing-man has excited great 

 admiration in those persons who have seen him act. 



But the experiment may be carried still further, by turning 

 to account an idea communicated to me by Mr. Wheatstone, and 

 which consists in combining the principle of the stereoscope 

 with that of the phenakisticope. By means of the stereoscope, 

 an ingenious instrument invented by the physicist I have just 

 named, objects dra^vn perspectively upon plane surfaces in out- 

 line appear, as is well known, to have three dimensions ; and the 

 illusion is such, that it is absolutely impossible to divest oneself 

 of it. Let us suppose, then, that we succeed, by the combination 

 of the two kinds of insti-uments, in adding this last effect to 

 those of the phenakisticope ; then figures simply painted upon 

 paper will be seen unmistakeably in relief and in motion, and 

 will thus present, in a complete manner, all the appearances of 

 life. This will be the illusion of art carried to its highest degree. 



Now the modification of the phenakisticope described in this 

 Note is eminently fitted to realize the combination in question. 

 It is known that the representation of an object in the stereo- 

 scope requires the simultaneous employment of two designs 

 having a certain relation between them, and placed on the two 

 sides of the apparatus ; it would suffice, therefore, to construct 

 two transparent discs, such that the figures should have one to 

 another the relation desired for the stereoscope; to fix these discs 

 to two systems similar to that whi(;h we have described, and 

 suitably adapted to tiic two extremities of Mr. Wheatstone's iu- 

 utrument; and lastly, to arrange so that the two systems should 



