16 EIGHTH REPORT — 1838. 



dantly, as to lead me to conclude that the gelatinous appearance of this 

 liumour, in its natural state, is a mere illusion, and that, in fact, it con- 

 sisted of a liquid no way gelatinous, inclosed in a sTructurie of trans- 

 parent and, consequently, invisible cells. The vitreous humour of the 

 other eye, insulated as far as possible, was therefore placed in a saucer, 

 and beaten up with a fork, in the manner of an egg beaten up for culi- 

 nary purposes. By this operation, the whole was resolved into a clear 

 watery liquid, in which delicate membranous flocks could be perceived," 

 and drawn out from the water in thready filaments, on the end of the 

 fork. From this experiment, it is clear that the vitreous humour (so 

 called) of this fish is no jelly, but simply a clear liquid, inclosed in some 

 close cellular structure of transparent membranous bags, which, by 

 their obstruction to the free movements of the contained liquid, imitate 

 the gelatinous state." 



On Binocular Vision ; and on the Stereoscope, an instrument for illus- 

 trating its 2)henomena. By Professor Wheatstone. 



Professor Wheatstone stated that, at the last meeting of the Royal 

 Society, he had pi'esented the first of a series of papers on the phe- 

 nomena of vision, in the investigation of which subject he had been 

 for some years engaged. On the present occasion he proposed merely 

 to state so much as would enable him to explain the experiments which 

 the appaiatus on the table was intended to exhibit. This apparatus he 

 called a Stereoscope, from its property of presenting to the mind the 

 perfect resemblances of solid objects. To understand the principles on 

 which it was constructed, he explained the circumstances which enable 

 us to distinguish an object in relief from its representation on a plane 

 surface ; he showed that when a solid object, a cube for instance, was 

 placed at a short distance before the eyes, its projections on the two 

 retinae fonn two dissimilar pictures, which in some cases are so different, 

 that even the eye of an artist would with difficulty recognise them as 

 representations of the same object ; notwithstanding this dissimilarity 

 of the two pictures, the object is seen single ; and hence it is evident 

 that the mind perceives the object in relief, in consequence of the 

 simultaneous perception of the two monocular pictures. He next 

 showed, that if the object were thus drawn, first as it appears to the 

 right eye, and then as it appears to the left eye, and those two pictures 

 be presented one to each retina, in such manner that they fall on the 

 parts as the projections from the object itself would, the mind perceives 

 a form in relief', which is the perfect counterpart of the object from 

 which the drawings have been taken : the illusion is so perfect, that no 

 effort of the imagination can induce the observer to suppose it to be a 

 picture on a plane surface. Professor Wheatstone described various 

 modes by which the two monocular pictures might be made to fall on 

 similar parts of the two retinas ; but he gave the preference to a method 

 which may be understood by the annexed diagram. 



