Reade, on a New Hemispherical Condenser. 
59 
round the orifice of the tube. The slides or discs are then to be 
heated in the flame of the lamp^ so as to drive off the 
moisture, and raise considerably the temperature, of the 
glass. The slide or disc, thus heated^ is to be placed over the 
mouth of the tube, and kept there till bright spots appear on 
its under surface. The spirit-lamp is then to be removed, 
and the glass allowed to cool. The process may be conducted 
with the two hands over the lamp, or 
the holder may be supported on a retort- 
stand, as is shown in figure 32, and the 
spirit-lamp removed for a time after each 
operation. Good results can only be 
obtained when the slide or disc is heated ; 
but if too much heat is used, the crys- 
tals are dissipated as soon as formed. 
When the operation is quite successful, 
we obtain one of the most beautiful of 
microscopic objects, and one of the very 
best illustrations of the value of the binocular microscope 
as a means of identification and diagnosis."^ 
On a New Hemispherical Condenser for the Microscope, 
and its use in illustrating an important principle in 
Microscopic Illumination. By the Rev. J. B. Reade, 
R s 
(Read May 8tli, 1861.) 
The condenser which I am now using has been so favor- 
ably received by several of my friends, that I am induced, at 
their request, to oflPer a description of it to the members 
of our society. I need scarcely say, that an unpretending 
single lens cannot be proposed as a rival to the almost per- 
fect combinations in use among us ; but it may, perhaps, 
take its place as an efficient adjunct to the microscopes of 
those observers who are disinclined, from one consideration 
or another, to procure more expensive apparatus. 
The condenser consists of a hemisphere of glass, about 
one and three-quarter inches in diameter, with an arrange- 
ment of stops by which difficult test objects are well defined 
under half-inoh object-glasses of 90° aperture. It is set 
in a thin brass ring, and screws upon a cylinder adapted, like 
other fittings, to the opening of the sub-stage of the microscope. 
* Tor a more detailed description of the mode of obtaining crystals of 
arsenious acid, consult a paper iu 'Beale's Archives/ No. iii, 1858, and the 
second edition of my 'Principles of Torensic Medicine/ in which several 
of the forms depicted here will be found figured. 
