208 ANNUAL OF SCIENTIFIC DISCOVERY. 



cess in photography, discovered by Prof. Delamotte, of King's College, London, 

 and which is said to be the most important improvement in this branch of art 

 which has been brought out since the discovery of the collodion process. 



The new compound, called oxymel, consists of acetic acid 7 fluid ounces, 

 distilled water 8 fluid ounces, and honey (despumated) 5 pounds. 



" By the help of oxymel, all the beautiful delicacy of the finest collodion 

 pictures may be obtained, with the convenience of the paper process, and with 

 much more certainty and much greater ease. Tourists may take a dozen or 

 two plates ready prepared, and during a week or a fortnight may expose them 

 in the camera as they may require, and in the evening, or even in a day after- 

 wards, may develope the pictures they have obtained at their convenience." 



PHOTOGRAPHIC VIEW OF A PORTION OF THE MOON'S SURFACE. 



M. Secchi, astronomer at Rome, has sent to the French Academy a photo- 

 graphic view of the part of the moon's surface in which stands the crater 

 named Copernicus. The scale is about ^-^o-^o- The photograph was not 

 taken direct from the moon, but from a design executed with great care on a 

 somewhat larger scale, and having for its base a micrometric triangulation of 

 the principal points of the area. The details were brought out with a lens 

 magnifying 760 to 1000 tunes : the work, seemingly easy, was attended with 

 great difficulties, on account of the change hi the shadows with every hour, 

 the moon's libration and change of distance. To avoid all these difficulties a 

 general sketch was first made under the most favorable light and view for 

 marking out the crater, such as is ordinarily had when the moon is ten days 

 old. After this, the details were separately mads out, and then all were 

 combined in their true relations, so as to make the complete sketch. The 

 result thus reached was corrected by several examinations made from the 

 first point of view. A professed draughtsman was occupied with the work 

 during seven consecutive lunations, without counting the tune employed 

 previously in practising preparatory to the work, 



As the drawing was intended to represent the great central crater, the area 

 around is not yet filled with all the details that may be introduced. After 

 completing the design with every possible care, M. Secchi has had copies 

 taken by photography, one of which he has sent to the Academy. The 

 crater or annular mountain has two circular walls. The outer, which is the 

 lowest, has a diameter of about 48 seconds (one second corresponds to 1-820 

 meters) ; the inner, the true border of the crater, has a mean diameter of 

 38 seconds, and has a peak, somewhat elevated, on its western side. The 

 inner area is 20 seconds across. The interior has a steep escarpment around, 

 and a triple circuit of broken rocks and a great number of large masses piled 

 up at the foot of the escarpment, as if they had fallen from above. There are 

 two great depressions in the north and south borders of the crater ; and it is 

 remarkable that in the direction of this line, outside, both north and south, 

 there are some small craters. 



After having established the perfect resemblance which exists between the 

 volcanic mountains of the environs of Rome and the lunar mountains (com- 

 paring with the chart of the Roman territory made by the French officers), 



