548 KANSAS CITY REVIEW OF SCIENCE. 
possible, the laws regulating their internal movements. Drawings have been 
made of some of the nebule, and especially of the nebule in Orion, for upward 
of 200 years. But drawings are open to the objection that fancy or bias may 
distort the picture, and it is therefore difficult to depend upon the result and 
compare the drawing of one man with that of another. To apply photography to 
depicting the nebulee is difficult, because these bodies are very faint,and, of course, 
owing to the earth’s motion and other causes, they seem not to be at rest. They 
require a large telescope of special construction, and it must be driven by clock- 
work with the greatest precision. All such difficulties as those arising from re- 
fraction, flexure of the telescope tube, slips of loose bearings, atmospheric tremor, 
wind, irregularities of the clock-work, foggy or yellow state of the air, have to be 
encountered. The photographic exposure needed is nearly an hour, and a slip 
or movement of a very small fraction of an inch is easily seen in the photograph 
when it is subjected to a magnifier. 
‘The means I have used to obtain what is now presented to the Academy 
are as follows: First, a triple achromatic objective of eleven inches aperture mark 
according to the plan of Mr. Lewis M. Rutherford, for correcting the rays es- 
pecially used in photographing. This telescope is mounted on an equatorial 
stand, and driven by clock-work that I have made myself. The photographic 
plates are bromo-gelatine, and are about eight times as sensitive as the collodion 
formerly employed. As to the picture itself, it will be observed in the copies be- 
fore you that the nebula is very distinct in its bright position. The stars of the 
trapezium, and some others, are so greatly over-exposed that under the magnily- 
ing power employed, namely, 165 times, they assume a large size, partly from at- 
mospheric tremor and partly from other causes. In the lower right hand corner 
of the picture is a photograph of the trapezium of only five minutes’ exposure, 
and this shows the individual stars plainly. The nebule present a knotted struct- 
ure, as if a process of aggregation was going on, but on this topic I will not make 
any statement until I have a larger collection of original negatives, so as to de- 
termine what effects different lengths of exposure will produce. I should add 
that itis more probable that much more of the nebulz will be obtained in the 
pictures taken in the clear winter weather. This photograph was made at the end 
of September, when there was some fog and yellowness in the air, but, neverthe- 
less, the original shows traces of the outlying streamers seen in the drawings of 
Lord Ross, Trewvalet, Band, Lassell and others. A series of photographs taken 
during various parts of the winter season, and in different years, will give the 
means of determining with some precision what changes, if any, are taking place 
in this body.” . 
Copies of the photograph in the form of an artotype enlargement were pre- 
sented, which will be preserved by the recipients as the first ever successfully 
executed. The negative was taken on September 30, the exposure being fifty-one 
minutes. The large stars of the constellation are somewhat indistinct from the 
over-exposure necessary to obtain an impression of the nebule. In the lower 
