On a Series of Lantern Slides. By Dr. A. Clifford Mercer. 317 
and Burrill beliostat * on a shelf-table. The window-sash is glazed 
with plate glass through which the light from the mirror passes 
without that deterioration which occurs when light passes through 
the wavy surfaces of an ordinary pane. The place for the beliostat is 
so marked that it can be within a minute accurately set and levelled 
over a meridian line cut in the surface of the shelf-table. I have 
neglected to say previously that the whole apparatus in the room is 
also accurately placed and levelled over an extension of the same 
meridian line cut in the floor. By referring to figs. 35 and 36 
it will be seen that the table-top expansion is not directly sup- 
ported by the three legs. The three legs support a ring into the 
lumen of which fits nicely but freely a circular plate of hard wood 
fastened centrally to and below the table-top expansion. This con- 
struction permits the camera and Microscope to be turned out of 
meridian while the revolving board remains in meridian for oblique 
illumination with sunlight. On returning the camera support to the 
meridian, cleats on the floor stop the instrument in correct position. 
In photomicrographing opaque objects by sunlight the heliostat is 
shifted to a meridian one foot to the east, as are also the alum and 
ammonio-sulphate of copper cells. The sunlight from the heliostat, after 
passing through the cells, is received by a long-focus concave mirror 
and reflected on the opaque object. 
Slide 55 (fig. 40) is a photograph of a Powell and Lealand No. 3 
stand with a side tube added for photomicrography and a lever 
attachment to the pinion of the draw-tube. The mirror, now in the 
side tube, can be moved into and out of the axial tube by means of 
the milled-headed screw seen under the side tube. It is obvious, too, 
that the use of the tubes can be reversed : the Microscope can be 
used in the vertical position, the object and illumination arranged in the 
ordinary way, then the mirror pushed into the axial tube to reflect 
the image-forming rays into a camera attached to the side tube. To 
the right is seen the adjustable standard for supporting the eye-end of 
the axial tube when horizontal. It is adjustable in height by means 
of the milled-head screw arrangement seen about one-fourth down 
the standard. 
A convenience peculiar to the Powell and Lealand, or Boss, model 
of stand is shown in slides 61 and 62 (not figured). The axial tube 
is removed and its supporting arm turned to one side. By means of 
stage forceps various large objects are supported, or on a broad wood 
superstage a bit of manuscript is flatly fastened, while a short-focus 
doublet landscape lens on the camera front serves, instead of a Micro- 
scope objective, to cover a comparatively extensive area and give a 
perfectly flat field. 
Exposures are made in a very simple way. While the sensitive 
plate is being placed, a black card stands close to the ammonio- 
* Proc. Amor. Stic. Micr., 188.5, p. 103. 
