CHAP, vin ] HELIOGRAPHY PHOTOLITHOGRAPHY. 327 



" At the present day thirty years have elapsed since the discovery 

 of Daguerre ; how have these ambitious hopes been realised ? 



" Warren de la Eue in England, William Cranch Bond in America, 

 and others, have bravely put their hand to the work. They have 

 adapted powerful astronomical glasses to photographic apparatus, 

 and they even succeeded in giving their apparatus, dining the short 

 interval necessary for producing proofs, the same movement as the 

 celestial bodies whose image they were trying to see. Thus the moon 

 has been photographed in her different phases ; but the details have 

 remained far below those to be discerned by an able observer. Bond 

 devoted his study to the fixed stars, and he employed a telescope 

 capable of showing stars of the fourteenth magnitude ; but he could 

 only obtain feeble and scarcely visible images of stars of the fifth 

 magnitude. 



"We might certainly allude to some very valuable drawings which 

 we owe to astronomical photography ; but it is not the details of the 

 starry sky that we can gain and preserve by this means : it is rather 

 the phenomena presented by objects long known and giving a powerful 

 light. 



" I will first allude to the spots on the sun, the reproduction of 

 which only requires a fraction of a second, and with a very accurate 

 result. Yet, even in this instance, the details are far inferior to those 

 which can be reproduced by able observers accustomed to these 

 phenomena ; but a very important point of its kind is gained, an 

 image of the sun at a certain moment, and, if I may be permitted to 

 use an expression of Sir John Herschel, the sun is forced to write for 

 us his own history. 



" These experiments will be, or, to be more exact, have already 

 been very useful, particularly in total eclipses of the sun. There is 

 no draughtsman, however expeditious he may be, who can do in two 

 or thiee minutes the ordinary duration of the phenomenon what 

 Warren de la Eue did in Spain on the last occasion of a solar eclipse, 

 for, supposing all to have been prepared beforehand, one may obtain 

 not only three, but twelve or fifteen images of a phenomenon which 

 disappears so rapidly. For the "planets, even the large ones, photo- 

 graphy is of little use, and will teach us few new things. It is 

 even less useful when applied to the stars. The groups of the Pleiades 

 and of Orion have been photographed, and one could recognize the 



