J. C. Draper— Projection of Microscope Photographs. | 259 
scribed no channel of outflow ; and it is evident, moreover, that 
he gave little thought to the subject, for he made the somewhat 
astonishing suggestion that four outflowing streams might have 
coéxisted—one at the Soda Spring Pass, one at Red Rock, one 
near Malade City, and one at the head of the Malade River. If 
he had seen the channel at Red Rock, I do not doubt that he 
Art. XXXVII.—On the Projection of Microscope Photographs ; 
ty JOHN CHRISTOPHER Draper, M.D., LL.D., Professor of 
atural History in the College of the City of New York. 
IN the lanterns that are constructed for the projection of pho- 
tographic or other images on a screen, the support or stage on 
which the photographic slide is placed is close to, and at an in- 
variable distance from, the condensing lens. So long as the ob- 
jects to be projected are nearly equal in size to the diameter of 
the condenser, this is the only adjustment that can be made to 
illuminate the whole surface of the object; but, when the 
diameter of the field occupied by the object is only one-half, or 
one-quarter of the diameter of the condensing lens, the_bril- 
lianey of the result obtained upon the screen may be greatly in- 
creased by removing the supporting stage or object carrier to a 
greater distance from the condenser, so that a convergent beam 
of light may fall on the object to be projected. T'o accomplish 
this I have constructed the following form of lantern: 
In the figure, a is a zirconia light, mounted on an adjustable 
base (see American Journal of Science and Arts, Sept., 1877, 
page 208), which may be used with a condensing lens of very 
short focus, since the zirconia is not burrowed into cavities 
Where the oxyhydrogen flame impinges, as happens with lime 
cylinders, and causes the flame to be reflected upon the con- 
densing lens and thereby destroys it. In the jet employed, the 
gases are mixed just before they are ignited. 4, , is a short 
focus condensing lens. ¢, the stage or support carrying the pho- 
tographie or other design to be projected. d, the projection 
