ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
107 
The highest power is a No. 4 Leitz ; this has been chosen, not only- 
on account of its being of the power that was required, but also because 
it makes a very fair low-power lens when the front lenses are removed. 
The complete lens gives a power of 100 diameters with the tube ex- 
tended, and 66 with the tube closed ; when the front lenses are removed 
and the tube extended, a power of 32 is obtained. We have, therefore, 
a range of power from 30 to 100 diameters with the one objective. 
The other lens, which Messrs. Watson have constructed at my 
suggestion, is somewhat of a novelty. It is made on the plan of the 
Zeiss a* with a concave front, but it differs from those lenses in as 
much as its aperture is greater and its mount is a rigid one. The 
range of power in this lens is more than twice as great as in the case 
of Zeiss a*. For example, on this instrument my Zeiss a* gives a 
range of power from 6 to 10 diameters, while the new lens on the same 
instrument gives from 5 to 20 diameters. This lens will be valuable 
for all kinds of low-power work, as it will do the work which now falls 
to the 3-, 4-, and 5-in. lenses. 
In bringing forward this instrument let me express a hope that it will 
open a wider field for research and extend the ever-growing popularity 
of the Microscope.’’ 
Fig. 5. 
C3) Illuminating- and other Apparatus. 
New Exact and Easily Constructed Spherometer.* — Signor G. 
Guglielmo has devised a new form of spherometer which can be easily 
constructed out of ordinary laboratory apparatus without the use of a 
micrometer screw. 
The apparatus is represented in fig. 5. A is a cylindrical or 
prismatic vessel covered with a glass plate in which two holes are bored. 
Through one of these holes there 
passes nearly to the bottom of the 
vessel the glass or indiarubber 
tube which is connected with the 
burette B. Through the other 
opening projects a glass or metal 
rod (C or C x in the figure) which 
possesses two points a and b and 
slides in the holder D. In order 
to work the apparatus, a liquid 
is poured into the cylindrical 
vessel and into the burette, and 
the level in A adjusted exactly 
to the point b. The plate, of 
which the thickness is to be mea- 
sured, is then placed on the glass 
plate beneath the point a. This 
will have the effect of raising b 
above the surface of the liquid. More liquid is then introduced from 
the burette until the level in the vessel is again flush with b. The 
* Atti d. R. Acc. d. Lincei. Rndct. (1893) I. 4. See Zeitschr. f. Instruraentenk., 
xiii. (1893) p. 393. 
