CHAP, vii.] PHOTOGRAPHY ON PAPER AND ON GLASS. 309 



First we obtain, from the negative a positive of the same size. 

 This we submit to the amplification of the solar microscope, so that 

 the enlarged proof is a negative. This proof is obtained on a collo- 

 dionized glass, which has been sensitized by the usual processes. 

 When exposed and fixed, the negative proof, enlarged to the required 

 size, supplies positives. In this way the enlarging optical apparatus 

 is only used once, and the rapidity of this method is very great. 



The difficulty in the enlargement of photographic proofs consists 

 in rapidly obtaining very clear proofs undistorted and preserving the 

 vigour of tone of the proofs obtained in the first instance. At first, 

 enlarged photographs were very unsatisfactory in these respects ; but, 

 by perseverance, they have been brought to wonderful perfection. 

 At the Universal Exhibition of 1867 might be seen a magnificent 

 full-length portrait, and an enlarged view of Amiens Cathedral , 

 which, composed only of four pieces, measured no less than two 

 metres in width and two and a half in height. Applied to astronomy, 

 we shall see that this method of enlarging, in the hands of able and 

 scientific operators, has produced remarkable results. 



The importance of this process not so much for ordinary views 

 and portraits, as for the reproduction of objects whose multiplied 

 details escape the pencil of the most patient and talented artist will 

 be understood. The wisli of Arago, with regard to Daguerre's inven- 

 tion, that faithful reproductions might be obtained of the thousands of 

 hieroglyphics covering the monuments of ancient Egypt, is realized 

 at the present day, thanks to the enlarging process in photography ! 



If the image, some centimetres in diameter, of a body like the 

 moon, may thus be transformed into a proof of a metre or more in 

 diameter, enabling us to study at leisure the orthographic configuration 

 of our satellite, how much more precious is the enlarging method for 

 fixing the thousands of images of those natural objects which, by 

 their minuteness, escape the eye ! To obtain this result, the clearest 

 possible images of these infinitesimal atoms had to be produced. This 

 object has been realized, and the result is an entirely new branch of 

 the art, microscopic photography. 



This new step is due, in a great measure, to M. Bersch ; who has 

 invented the optical instruments necessary for the production of 

 microscopic images, for their subsequent amplification, and the 

 arrangements necessary for the different operations required in their 



