862 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
The two speculum-metal centimetres above referred to, with their 
investigation as made by Prof. Rogers, will subserve the purpose of 
substandards, and the five glass centimetres can be used by observers 
for the verification of their glass stage micrometers, so that there need 
be hereafter no occasion to use ‘ Centimetre A,’ except as a final standard 
of reference. I would therefore respectfully recommend that ‘ Centi- 
metre A ’ be deposited with the Superintendent of the United States 
Coast and Geodetic Survey, and that hereafter the two speculum centi- 
metres be the working standard of the American Society of Micro- 
scopists.” 
Revolving Stage for Viewing Microscopic Sections, &c.* — Dr. T. 
Taylor, the chief of the Division of Microscopy in the U.S. Department 
of Agriculture, has devised a stage of which he gives the following 
account : — 
“ This plate exhibits a view of a new and improved form of revolving 
brass plate which I have recently devised in order to supply a need 
long felt in the division. It may be attached to any Microscope, and is 
designed principally for reviewing and comparing serial sections and 
textile fibres. This revolving plate is pivoted upon the substage by 
means of a downward-projecting pin. It may thus be rotated freely at 
the pleasure of the operator. Slides mounted with subjects for investi- 
gation and comparison are secured by means of spring clips upon the 
surface of the plate. 
A stage of this description which I am accustomed to use exhibits 
eleven different samples of wools. In jury trials relating to wools I 
have found it sometimes desirable to have six Microscopes in use at one 
time in illustrating the respective characteristics of various samples of 
wool. Even with this number the parties are seldom satisfied, as one 
person is obliged to move from one instrument to another, interfering, 
perhaps, with the view of other observers. The system I have initiated 
saves much time — an important consideration in the court-room. By 
means of the revolving plate eleven diverse samples may be compared in 
less time than an observer could move from one Microscope to another. 
Six stands of this model were on exhibition at the fourteenth annual 
meeting of the American Microscopical Society, recently held in this 
city, and the invention gave universal satisfaction. The publishing 
committee of the society have requested a description of this plate for 
the forthcoming volume of Proceedings. 
I use a similar form for high powers, consisting of perfectly clear 
glass 2 mm. in thickness, circular in form, like the preceding, and, like 
it, attachable to the plane stage of a Microscope. On this plate the 
objects may be arranged upon its margin, the same as on the usual glass 
slides, and the cover-glass fixed upon them, thus dispensing with clips, 
which interfere somewhat with the objective when using high powers. 
Or the plate may be perforated, as in the metal plate, the mounts fixed 
by means of wax or a drop of paraffin at the edges of the slides. This 
method, I find, renders the object sufficiently steady for examination, 
and the wax has the advantage of being easily removed when it has 
answered the purpose, leaving a clean plate for change of subject or 
* Report of The Microscopist for 1891, pp. 413-4. 
