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Transactions of the Society. 
nation.* This has an arc lamp fitted with mechanism for hand control 
of the carbons ; there is also a subsidiary image of the carbons cast on a 
side screen for the purpose of assisting regulation ; by these means a 
perfectly steady light can be maintained. The drawback in the use 
of the arc light for photomicrography seems to he that unless a bull’s 
eye is employed it is hardly possible to cover any ordinary object, 
because the image of the incandescent crater as minified by the sub- 
stage condenser presents such an exceedingly small surface. 
Mr. E. B. Stringer’s photomicrographic camera f is very elaborate, 
being fitted with a powerful condensing apparatus, each portion of 
which is capable of being independently centred. The specially 
interesting feature in this instrument is the control of the gas and the 
beautiful and uniformly illuminated disc of zircon, -which is about 
1 /4 in. in diameter. 
Next we have a binocular dissecting Microscope by Zeiss t fitted 
with two objectives ; the eye-pieces having Forro erectors by which 
an ortho-stereoscopic image is obtained. This apparatus is only suit- 
able for low powers, but yields very beautiful effects. 
Finally, two ancient Microscopes have been presented to the 
Society. The first being a second contribution to our cabinet by 
Mr. James More, jun., of a Microscope of the Culpeper type ; § this, 
which is fitted with a rackwork adjustment, was probably made by 
Jones (joost 1797). The other, the gift of Mr. George T. Harris, is 
an older example of the same pattern ; || in this the octagonal box foot 
is retained, the legs are slightly scrolled, and the body is covered with 
shagreen ; its date may be put back to circa 1750. 
Those about to name new diatoms should, before doing so, read 
Mr. T. Comber’s excellent paper H on ‘ The Limits of Species in the 
Diatomaceae.’ 
Two interesting old Microscopes have been lent for exhibition. 
One formerly belonged to Sir I). Brewster,** with which he worked 
until the year 1838. This contained the garnet lens which was con- 
structed for the purpose of reducing the spherical aberration, but 
which in reality introduced greater errors than it was intended to 
remove. 
The second old instrument was a Powell and Lealand,tt which was 
important, inasmuch as it possessed a transitional form of fine adjust- 
ment. 
With regard to Microscope objectives, while apochromatism remains 
for the most part where it was, considerable progress has taken place 
during the past few years in the improvement of semi-apochromats. 
The colours of the uncorrected dispersed rays have become less violent, 
* Journal R.M.S., 1897, p. 600. An extended account of this is in press. 
t An account of this is in press. 
+ Journal R.M.S., 1897, p. 602. § Tom. cit., p. 181, and 1898, p. 126, fig. 4. 
|| Op. cit., 1898, p. 126, fig. 3. f Op. cit., 1897, p. 455. 
** Made by Doliond, Journal R.M.S., 1898, p. 123, fig. 1. 
ft Journal R.M.S., 1898, p. 125, fig. 2. 
