Trans. N. V. Ac. Sc/. 144 Mar. 20, 



about one inch in d'ameter. Daguerre had attempted the same thing, 

 but did not succeed. This is the first time that anything hke a distinct 

 representation of the moon's surface has been obtamed. 



(Signed) ROBT. H. Brownne, Secretary. 



Since that time celestial photography has been immensely improved. 

 When we read the names of the men who have done the most to 

 develop this beautiful branch of investigation, we find that a member 

 of the New York Academy of Sciences stands at the head. 



To Lewis M. Rutherford the world of science owes a great debt 

 for his untiring perseverance and ingenuity, shown in developing Celes- 

 tial Photography to such a point that it now bids fair to replace, in a 

 great measure, all other methods of observation. 



[The general outlines of the method of photography were given, 

 the several obstacles to be overcome were mentioned, and the plate- 

 holder illustrated and explained. The necessity of having a good clock 

 was shown. The differences between reflectors and refractors for 

 photographic work were illustrated, several advantages of each kind of 

 instrument being mentioned.] 



As a piece of interesting history relating to our subject, let me quote 

 from an English work. Chambers' Descriptive Astronomy. 



"To an American we are indebted for the best pictures of our satel- 

 lite yet produced, and it is difficult to conceive that anything superior 

 can ever be obtained ; and yet with the fact before us that De la Rue's 

 are better than anything taken in this country, so it may prove that 

 even the marvellous pictures of Mr. Rutherford may be surpassed." 



Mr. Rutherford appears, from a paper in Silliman's American 

 "Journal of Science for May, 1865, to have begun his work in lunar 

 photography in 1858, with an equatorial of 11/4^ inches aperture and 

 fourteen feet focal length, and corrected in the usual way for the visual 

 focus only. The actinic focus was found to be i^j of an inch from the 

 visual. The instrument gave pictures of the moon, and of stars down 

 to the fifth magnitude, satisfactorily, when compared with what had 

 been done previously, but not sufficiently so to satisfy Mr. Ruther- 

 ford. After trying to correct for the photographic rays by work- 

 ing with combinations of lenses inserted in the tube between the object 

 and the sensitive plate, he commenced some experiments, in 1861, with 

 a silvered mirror of 13" diameter. This was mounted in a frame and 

 strapped to the tube of the refractor. Mr. Rutherford enumerates 

 several objections to the reflector for this kind of work, but admits the 

 advantage of coincidence of foci. The reflector was abandoned for a 

 refractor, specially constructed, of the same size as the first one and of 

 nearly the same focal length — about -,^j shorter. This instrument was 

 corrected for the chemical rays only, and was, therefore, worthless for 



