568 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
about care in using high power objectives, and warning of the danger of 
racking downward, &c. Having to use a fine, high power, dry objective 
of very short working distance, always nearly or quite touching the 
cover-glass when in focus, it is well known that the thickness of a series 
of cover-glasses of the same number varies greatly ; hence, one of a 
package could be worked through, while another could not. 
Looking across the stage and carefully racking down until the front 
of the lens was so close to the cover that I could not see between them 
with a hand-lens, thereupon applying the eye to the eye-piece, and 
manipulating the screw of the fine-adjustment, I often found that I was 
still above the focus, and it became an important consideration as to how 
close I could press the cover-glass with safety and advantage when 
searching for an object mounted in aqueous or glycerin medium. 
The little accidental motes when seen moving about in the medium 
sounded a note of alarm and said, ‘You can go no closer; even now 
there is danger.’ I have a so-called safety nose-piece in my possession, 
a contrivance with a spring in it between the tube and the objective, to 
prevent unbearable pressure, but it is not always on the stand ; more- 
over, it is a troublesome thing in changing objectives where the stand 
has a short working distance, for it makes quite a long affair to handle 
and not touch the cover-glass in changing lenses after using a low power 
as a finder. This safety spring admitted of an unpleasant pressure, 
sometimes causing the mounting fluid to swell over the cover-glass, 
sometimes getting on to the lens, greatly to my annoyance. At this 
junction I looked about me for a better remedy than the safety nose- 
piece to use in my studies of objects on slides not finished by drying and 
sealing in a permanent mount. I then began to use the short slide as 
presently to be described. It was a new idea to me ; whether new or 
not to other and more experienced workers, I cannot tell, but I do not 
remember having ever seen it mentioned in any of the microscopical 
books or journals at my command. I formed, in this way, a preference 
for slides 2 in. long and 7/8 in. wide, finally coming down to 1 in. and 
3/4 in. long, and corresponding in length with the excellent short slides 
furnished by the Bausch & Lomb Optical Company, and very nearly 
corresponding with the length of the German slides furnished by Zeiss, 
of Jena, and to be had of Emmerick, in New York. Both of these, 
however, I found too wide for using as safety slides with my apparatus, 
the opening in the slide carrier on my No. 560 Bausch and Lomb stand 
being just an inch wide. I therefore was obliged to get the best, 
clearest glass I could find, and make my own slides, 7/8 and 3/4 in. 
wide by 1 and 3/4 in. long. A fine file or a piece of scythe whetstone 
rubbed over the edges and corners removes any sharpness, and is quickly 
done. A thousand slides of this kind can be easily and quickly made, 
and will answer every purpose in ordinary work. By mounting the 
object in one end I have a safety slide. 
Place the slide so that the mounted end, when projecting over the 
opening in the stage, is free in air. Now it is apparent that when thus 
placed under the close- working objective it cannot be injured, because, 
when the point of the objective presses on the cover-glass ever so 
slightly, it can make no more than this slight pressure, for the slide, 
being placed see-saw- like over the opening, will begin the dip of the see- 
