446 
PROCEEDINGS OF THE SOCIETY. 
features that are not present on other microscopes in the Society’s 
collection. 
The first is an Andrew Ross, a very old model, with a plain stage 
having a sliding plate, a wheel diaphragm, two capped eye-pieces, 
objectives 1 in. and J in. 
The next instrument, by Smith, Beck & Beck, has the flat form of 
foot to be found on many of Messrs. Beck’s stands of that period, a 
foot which is particularly rigid. It is provided with coarse and fine 
adjustments, plain stage with sliding object carrier, underfitting ring 
with wheel , diaphragm, while the accessory apparatus consists of a double 
nose-piece, an erector, two capped eye-pieces, objectives § in. and ^ in., 
and three dark ground stops. Attention must be called to the fine 
adjustment on this instrument. There is not such another fine adjust- 
ment in the collection. The milled head exerts a direct pull from the 
under surface on the pillar supporting the microscope body, and it 
would appear that this principle must have been the parent of the 
micrometer fine adjustment, either by direct acting screw or against a 
spring introduced at a later date by the Germans. 
The third instrument is made by James Swift, and represents an 
exceptionally complete outfit. The stand has been developed not only 
for petrological, but for ordinary biological purposes. It is interesting 
here to note that both the analyser and binocular prisms are removable 
at will, and for use as a monocular a separate tube replaces the binocular 
drawtube. This, instead of being cut away, as is the method with the 
binocular microscopes, is solid throughout its length, thus preventing 
any stray light, and it projects beyond the length of the ordinary 
tube in order that no confusion may arise. The rotating stage 
has a rackwork movement, and the rotation divisions are on silver. 
A mechanical stage is provided with sliding bar, and here again the 
divisions are on silver. The substage is of the rack focussing and screw 
centring type, while centring screws are fitted to the stage. The com- 
bined condenser, which appears to be of the Webster achromatic type, 
and the polarizer, were probably introduced by Messrs. Swift, and special 
attention should be given to the iris diaphragm, which is a very early 
one and well made. The condenser has rotating cells for the selenites 
and mica dark ground stops, a pin-hole disc, glass discs, two selenites, 
and one J-wave plate mica. In addition to this, the accessories with 
the instrument comprise : one micrometer eye-piece with micrometer, 
three pairs of capped eye-pieces, one each capped eye-pieces D and F, 
one quadruple nose-piece, one Bertrand’s lens, and frog plate. The 
objectives are Messrs. Swift’s best series, the powers being 4 in., J in., 
4 in., and in. immersion. All are provided with correction collars. 
Mr. Conrad Beck exhibited a new and inexpensive microscope, in 
waterproof canvas case, and was thanked for his exhibit. 
A paper by Mr. S. C. Akehurst, “Larva of Chaoborus crystallinus 
(De Geer) (Corethra plumicomis F.),” was read in title. 
