THE BRITISH ASSOCIATION AT YORK. 231 
the latter has been made to coincide with the optical axis of the 
object glass. This will enable the microscopist to illuminate the 
whole field of a }-inch object glass through an aperture of 1-1ooth 
of an inch in diameter. But it can only practically be done by a 
fine set of mechanical motions in rectangular positions, giving per- 
fect command of the position of the flame. 
There was also exhibited an apparatus for continuous observa- 
tion of minute organisms, with the highest powers, by preventing 
evaporation of the fluid in which the organisms live. ‘This appa- 
ratus was devised by Messrs. Dallinger & Drysdale, for prosecuting 
their “‘ Researches into the Life History of the Monads.” It is 
used upon the ordinary mechanical stage of the microscope, so as 
to admit of the continuous examination under the highest powers 
of the same drop of a putrefactive or other fluid without allowing 
it to evaporate. The capillarity of the linen carries over a constant 
supply of moisture; part of this linen is included in a central 
cylinder, into which the object glass projects, and the water thus 
constantly carried into this air-tight chamber causes the air therein 
to become so saturated that evaporation from the fluid, under 
examination, cannot take place. ‘The highest powers may be used, 
as the india-rubber diaphragm yields instantly to the screw of the 
“fine adjustment.” 
An apparatus for studying the effects of successive applications 
of heat to the freshly emitted spore of the septic organisms, with- 
out allowing access of air from without after hermetically sealing, 
was also shown by Mr. Dallinger. The instrument consists essen- 
tially of a flat round cell, with extremely thin floor and roof, and 
with a very narrow space between. ‘This cell is in communication 
with a bulb, in which is the septic fluid suitable to the organism 
whose spore is being subjected to heat. The spore, just seen 
to be emitted from the sac under a suitable lens, is by arrange- 
ments detailed in the Proceedings of the Royal Society, inserted 
in the bulb; which is then subjected as a whole to the heat 
required, and hermetically sealed. The heating, however, drives 
off the air; its absence might be an injurious factor in the ex- 
periments. Hence the second bulb above the large one containing 
the fluid is so placed, that it is divided from it by a very thin 
septum ; a piece of platinum is placed loosely in it, and it is filled 
with calcined air and closed. Hence when, by heating the septic 
fluid, the air is driven off, and it is closed, the calcined air in the 
upper bulb is introduced by shaking the piece of free platinum 
upon the thin septum, which breaks it, and the air it contains is 
diffused in the closed bulb with its cell. By placing the whole ina 
cradle the behaviour of the spore may be studied with high powers 
in the flat cell referred to. 
Further on were to be seen a collection of mineral and rock 
