NATURAL PHILOSOPHY. 1-15 



nize them, cannot embrace any of the rays of light which come from 

 those parts of the object which lie in such positions towards the sides, 

 top, bottom, or hinder parts as cannot pass in straight lines to an aper- 

 ture of the size of the pupil, in fact, unless it agree almost exactly 

 with the exact perspective form of the object, the pupil being the point 

 of sight. If, then, an object be placed before a lens, the part of the 

 lens towards its centre of the size of the pupil is capable of forming 

 a correct image of that object, consisting of rays coming from pre- 

 cisely the same parts of it as an eye would receive were its pupil in 

 the same position. But all the parts of the lens or mirror of the same 

 size which lie around and at a distance from this portion of it, would 

 receive rays coming from parts of the solid object which the true eye 

 could not receive, and which must therefore form as many unnatural 

 images as there Avere such parts ; and the photographic picture which 

 embraces and confounds into one hideous mass all these, anv one of 



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which by itself would be correct, must in the very nature of things 

 give a most confused and displeasing representation of the object. 

 Sir David illustrated and proved these assertions by a diagram of a 

 Lens with a simple solid form, a cylinder topped by a cone behind, 

 placed in front of the lens, pointing out the parts which alone could 

 be embraced in a correct perspective view of it, and what parts the 

 large lens or mirror would moreover receive and transmit rays from, 

 to be jumbled in the photographic picture with that which would alone 

 give a correct idea of the object as seen. He showed from the now 

 familiar illustration afforded by the binocular stereoscope, how very 

 dissimilar Avere the pictures of the same object received by small 

 lenses placed as near as the two pupils of the human eye ; images so 

 distinct that a child could readily distinguish them ; and yet multitudes 

 of such images were all received and jumbled together in those pho- 

 tographic pictures where lenses or mirrors of that or larger say 

 three or four inches aperture were used. "The photographer, 

 therefore," said Sir David Brewster, " who has a genuine interest in 

 the perfection of his art will, by accelerating the photographic pro- 

 cesses with the aid of more sensitive materials, be able to make use of 

 lenses of very small aperture, and thus place his art in a higher posi- 

 tion than that which it has yet attained. The photographer, on the 

 contrary, whose interests bribe him to forswear even the truths of 

 science, will continue to deform the youth and beauty that may in 

 ignorance repair to his studio, adding scowls and wrinkles to the noble 

 forms of manhood, and giving to a fresh and vigorous age the aspects 

 of departing or departed life." He then produced an exact diagram 

 of photographic images of a simple object produced by Mr. Buckle of 

 Peterborough. The acting diameter of the lens was 3 inches ; and 

 by using it with all covered, except a central space of 2-10ths of an 

 inch diameter, and then along with this space exposing circular spaces 

 of the same size towards the outer circumference of the aperture, the 

 effect of the combination of the marginal pictures was most distinctly 

 exhibited and demonstrated, by halos extending round the true image, 

 and the sharp cross lines ruled* on the object and shown in the iniag 



