1882. 145 Trans. N. Y. Ac. Sez. 
seeing. The glass was completed in December, 1864; but it was not 
‘until March 6 of the following year that a sufficiently clear atmo- 
sphere occurred, and on that night the negatives were obtained, from 
which the pictures of the moon that we shall see to-night were taken. 
But even with this method Mr. RUTHERFORD was not satisfied. 
Coming back to the 11-inch object glass which he had used at first, 
he determined to see whether or not the addition of a meniscus lens, 
outside the front lens, would not give him the requisite shortness of 
focus and bring the actinic rays absolutely together. By this arrange- 
ment he got a telescope which can be used for all purposes of astro- 
nomical research, and he has also eclipsed all his former efforts.—(Lock- 
yer, Star-gazer, p. 467.) 
In the series of moon-pictures by RUTHERFORD and DRAPER, we 
have a complete map of the mcon ; not only are the grander outlines 
clearly shown, but many of the smaller details. [Illustrations were given 
of the work of BEER and MAEDLER, of Germany, and SCHMIDT, of 
Athens. Comparisons were made between the photographs and eye- 
drawings, and the use of photography in detecting changes in the 
moon was alluded to. ] 
In taking sun-photographs, it becomes necessary, on account of the 
dazzling brightness of the sun’s light, to make the exposure practically 
instantaneous. Some astronomers reduce the aperture of their tele- 
scopes, by suitable diaphragms, to about two inches diameter, thus 
cutting off a great deal of the sun’s light. Even then, the time of ex- 
posure is less than the three hundredth part of a second. [The method 
of making these quick exposures by what is called the instantaneous slide 
was explained, A series of pictures of the sun, by Mr. RUTHERFORD, 
was then thrown on the screen. The use of photography, in studying 
the mottled surface of the sun, was illustrated by photographs from 
RUTHERFORD and JANSSEN, and drawings trom NESMITH, SECCHI, 
HUGGINS and LANGLEY. | 
There are times when the sun shows us surroundings which it is im- 
possible to see ordinarily, as at total solar eclipses. Such atime is an 
exciting moment, the eclipse lasting from a few seconds to some six or 
eight minutes only, and the average time being such that altogether we 
have only a few days in a century for observation. Drawings made 
by two observers, side by side, differ very peculiarly. Photography as- 
sists us immensely in our study, and some of the best observations of 
eclipses have thus been made. [lllustrations of the photographs ot 
1851, 1860, 1869, 1870 and 1872 were then thrown on the screen and 
explained. A full description was given of the apparatus used by 
the American parties, in photographing the transit of Venus, and some 
illustrations of actual photographs taken were shown.] 
