SCIENTIFIC SUMMARY. 
511 
here describe Mr. Smith’s contrivance, for its mechanism is complex, and the 
description in the inventor’s paper occupies a couple of pages. The reader is 
referred for details to Silliman's Journal , No. 123. Mr. Smith says the 
mechanical finger can be moved about with the utmost precision over every 
part of the stage, and can be employed to shift the position of such delicate 
structures as diatomaceee. 
The Exhibition of Microscopic Objects to Classes is attended with difficulties, 
since each object has to be placed separately on the stage. To obviate this, 
Dr. J. Barker, of the College of Surgeons, Dublin, suggests a plan for placing 
a number of slides so that they may without difficulty be brought successively 
beneath the microscope. This contrivance consists of a large disk of wood 
with a number of round openings near the circumference, of about an inch 
in diameter, over each of which a slide is placed and retained in its position 
with the object over the aperture, by an elastic ribbon passed through some 
round holes in the disk. The disk itself is fastened to the stage by a 
piece of propelling brass work, made to fit and hold in the central 
opening of the stage, and projecting out beyond the stage in front, and 
bearing the pivot or axis adapted to the centre of the disk, and on which 
it revolves. Dr. Barker thinks the apparatus of great advantage for class 
demonstration, but we have very serious doubts as to the benefits attending 
its employment. 
Section of Hard Structures. — Dr. Halifax gives the following account of 
the method followed by him in the preparation of the sections of hard parts 
of insects, etc. He thinks that glass is the best surface on which to cut the 
parts ; it seems to do less injury to the razor’s edge than other substances, 
whilst by offering a perfectly unresisting medium it allows of the sections 
being made regularly and with uniformity. The razor works very easily over 
the surface, and is less liable to injury from scratches. The object must, of 
course, be fixed, in order to be available for the cutting of the razor ; and this 
he effects by placing the object in a paper cell, and imbedding it in wax. Then 
the plug or block, which is to be received by the well of the cutting instrument, 
will consist of a little cylinder, made up partly by a small cylinder of wood, 
and partly by a small cylinder of wax, and wax contents. In some cases 
the objects become almost useless, from the difficulty of removing the 
wax afterwards ; and, to avoid that, he previously immerses the object 
in stiff gum, and allows it a very short time to harden before inserting 
it in the wax capsule. — Vide Proceedings of the Microscopical Society of 
London. 
A Graduating Diaphragm of an ingenious kind has been constructed by 
Mr. S. B. Kincaid. It consists simply of a piece of India-rubber tubing 
stretched between two brass cylinders, one of which slides within the other. 
When the cylinders are caused to revolve on their common axis, and in op- 
posite directions, the tube becomes twisted ; by this means its bore can be 
diminished to any required extent, whilst a central, uniformly round aperture 
is always preserved. We have not seen Mr. Kincaid’s apparatus, and cannot 
speak therefore as to its efficiency. 
A New Form of Leaf Holder , and also a revolving slide holder for the 
microscope, combined with a selinite stage, have been described by Mr. 
James Smith, F.L.S., in the Microscopical Journal for July. 
