140 REPORT — 1859. 



has been found preferable not to magnify the focal image, but to take enlarged 

 positive copies on glass direct from the original negative, by means of an 

 enlarging camera, and in this way the impressions, 8 inches in diameter, 

 exhibited at the Meeting were produced. 



In making positive copies, some of the more minute details are, unfortu- 

 nately, always lost, for no means exist by which enlarged positive copies can 

 be produced showing all the treasures of the original negative ; a perfect 

 enlarging lens being still a desideratum*. As an instance may be cited the 

 streak in the lunar disc, which Mr. James Nasmyth has called " the railroad," 

 indicated in Beer and Madler's map as a straight line to the east of the 

 crater Thebit between latitude 19° and 23° south, and between longitude 7° 

 and 9° east. In the photograph it is shown to be a crack in the lunar crust 

 with an irregular outline, and the eastern edge is perceived to be depressed 

 below the western, which forms a perpendicular clitf. This, although sharply 

 denned in the negative, is frequently lost in positive copies. For the exami- 

 nation and micrometrical measurement of the minuter details which celestial 

 photography is capable of furnishing, recourse must still be had to the 

 original negative. 



Notwithstanding the disturbances which arise from the atmosphere, minute 

 irregularities in the driving-clock, and the want of means for following the 

 moon's motion in declination, I have obtained pictures of the moon that bear 

 examination with the three-inch object-glass of a compound microscope 

 magnifying about 16| times, and which show with good definition details 

 occupying a space less than two seconds in each dimension. Two seconds 

 are equal to about g-g- th of an inch on the collodion plate in the focus of 

 my telescope, and in the finest photographs, details occupying less than yoVo tn 

 of an inch are discernible with the three-inch object-glass ; hence much 

 valuable work has already been accomplished. A second on the lunar sur- 

 face at the moon's mean distance being about one mile (1'149 mile), it will 

 be evident that, selenological disturbances, extending over two or three miles, 

 would not escape detection, if such occur, provided photographs continue to 

 be taken for a sufficiently long period. 



Lunar Phenomena recorded by Photography. 



Full Moon. — Variations of apparent Diameter. — By the delineation of our 

 satellite, photography brings out palpably several phenomena which, although 



well known, are not always present to the mind ; for example, about every 

 29 days it is stated that there is a full moon, but we see by the photographic 

 picture that there never is a full moon visible to us, except just before or just 



* Mav 1860. — As these sheets are passing through the press, the author has been in- 

 formed by Mr. Dallmeyer (son-in-law of the late Mr. Andrew Ross) that he has brought 

 his investigations on this subject to a successful termination, and that he has just produced 

 enlarging and diminishing lenses which copy without any sensible distortion or dispersion. 



