72 THE AMERICAN MONTHLY [ April, 
and a drop taken off the lower end upon a slide, to be examined at leisure 
with the microscope. The cap, ground and fitted upon the lower end, is put 
there as a precautionary measure, as will be seen farther on. 
The tube shown at 4 1s, we think, an improvement upon all of the fore- 
going, for, upon it there is no side aise to break off, and everything is com- 
prised in a small space. As will be seen by referring to the figure, there is 
a slight enlargement in the ground portion of the stopper-end of the tube, 
this protuberance coming down about one-half the length of the stopper, 
which is solid and ground to fit perfectly. The lower half, however, is pro- 
vided with a small longitudinal slit or groove, the lower end of which com- 
municates with the interior of the tube, whilst the upper end just reaches the 
enlargement in the side of the latter. Thus, in one position of the stopper, 
there is a communication between the tube and the outer air, whilst in all 
other positions the tube is quite shut. In all these tubes care must be taken 
to fill them completely with the urine, and to allow no bubbles of air to remain 
therein. 
The first of these settling tubes was made without the ground cap on the 
lower end, the latter being inserted into a small test-tube for safety. At the 
suggestion of Mr. J. L. Smith the test-tube was made a part of the appara- 
tus by fitting it (by grinding) upon the conical end, and in its present form 
it serves to protect the latter from dust and to prevent evaporation of the urine 
(or other liquid) and consequent deposition of salts, if, for any reason, the 
user should allow the tube to remain suspended for several days. 
These tubes will be found very useful for collecting and concentrating into 
a small bulk the sediment contained in any liquid, whether it be composed 
of urinary deposits, diatoms in process of being cleaned, or anything of like 
nature ; and, as the parts are all of glass, the strongest acids may be used, 
excepting, of course, hydro-fluoric acid, without harm to the tubes. 
March 11, 1887. 
The Zeiss Workshops at Jena. 
. J. Mayall, Jr., of the Royal Microscopical Society, detailed at the — 
wae meeting of the Society an account, of his recent visit to the ‘ Mecca 
of Microscopists.’ He received every attention from Professor Abbe, and 
could follow, in the fortnight of his stay, all the technical processes employed. 
It would hardly be possible to overrate the skill exhibited in the organization 
of the manufactory. Three hundred are employed, and the shops are so ar- 
ranged that those departments where the most delicate work is done are quite 
isolated from the j jarring of those where steam-power is in use, the casting and 
rough brass-work being all done on the premises. Only a small portion of 
the optical work is done by the aid of steam-power. The plank surfaces of 
eye-piece lenses were worked together in large sets. The glass slitting- 
machine, a rapidly-revolving iron disk, charged on the edges with diamond 
dust, was used in the preparation of prisms of different samples of glass to 
determine the refractive and dispersive indices. The slitters were used to cut 
out plates of optical glass of various required thickness ; these were then cut 
into squares and snipped to approximately a disc-shape by the grinders. 
These then cemented them upon a suitable block and ground and polished 
the surfaces upon metal tools attached to foot-lathes. The accuracy of the 
finished surfaces, was tested by Fraunhofer’s method, which consisted in pro- 
viding for each curvature required a pair of highly-finished standard convex 
and concave surfaces worked in rock-crystal, of which the radii had been 
accurately determined by means of a spherometer of great precision, the per- 
