Curiosities of Science. 47 



lenses, which increase the force of the action ; the binocular lenses, 

 which do the work of the stereoscope ; nor of the innumerable other 

 mechanical aids which have sprung up for its use. 



THE STEREOSCOPE AND THE PHOTOGRAPH. 



When once the availability of one great primitive agent 

 is worked out, it is easy to foresee how extensively it will assist 

 in unravelling other secrets in natural science. The simple 

 principle of the Stereoscope, for instance, might have been 

 discovered a century ago, for the reasoning which led to it 

 was independent of all the properties of light ; but it could 

 never have been illustrated, far less multiplied as it now is, 

 without Photography. A few diagrams, of sufficient identity 

 and difference to prove the truth of the principle, might have 

 been constructed by hand, for the gratification of a few sages ; 

 but no artist, it is to be hoped, could have been found possessing 

 the requisite ability and stupidity to execute the two portraits, 

 or two groups, or two interiors, or two landscapes, identical in 

 every minutia of the most elaborate detail, and yet diffe/ing 

 in point of view by the inch between the two human eyes, by 

 which the principle is brought to the level of any capacity. 

 Here, therefore, the accuracy and insensibility of a machine 

 could alone avail ; and if in the order of things the cheap popu- 

 lar toy which the stereoscope now represents was necessary for 

 the use of man, the photograph was first necessary for the ser- 

 vice of the stereoscope. Quarterly Review, No. 202. 



THE STEREOSCOPE SIMPLIFIED. 



When we look at any round object, first with one eye, and 

 then with the other, we discover that with the right eye we 

 see most of the right-hand side of the object, and with the left 

 eye most of the left-hand side. These two images are combined, 

 and we see an object which we know to be round. 



This is illustrated by the Stereoscope, which consists of two 

 mirrors placed each at an angle of 45 deg., or of two semi-lenses 

 turned with their curved sides towards each other. To view 

 its phenomena two pictures are obtained by the camera on pho- . 

 tographic paper of any object in two positions, corresponding 

 with the conditions of viewing it with the two eyes. By the 

 mirrors on the lenses these dissimilar pictures are combined 

 within the eye, and the vision of an actually solid object is 

 produced from the pictures represented on a plane surface. 

 Hence the name of the instrument, which signifies Solid I see. 

 Hunt's Poetry of Science. 



PHOTO-GALVANIC ENGRAVING. 



That which was the chief aid of Niepce in the humblest 

 dawn of the art, viz. to transform the photographic plate into 



