The Presidents Address. 
59 
angles to eacli other. This arrangement is very convenient 
for the display of both sets of lines in that difficult object, 
the Amician test. A similar plan, I believe, exists in the 
Kev. J. B. Readers hemispherical condenser. 
Mr. Eichard Beck's " Sorby Illuminator^^ well deserves 
mention. It was specially constructed for those examinations 
of metallic and other mineral bodies, the structure of which 
has been elucidated by Mr. Sorby. 
It consists of a large parabolic reflector attached to the 
objective. This affords a brilliant illumination of an oblique 
character ; and by turning a milled head, a second small flat 
mirror becomes so placed as to stop all action of the parabolic 
mirror, and substitute for it an illumination which is nearly 
vertical. The effect is very striking, and often exceedingly 
instructive. If, for example, we have a transparent mineral 
under inspection, slanting illumination gives one information 
to be obtained by a very penetrating view, while the vertical 
one almost destroys penetration, and brings out minute 
scratches and markings on the surface. This apparatus is 
best adapted for powers varying from 1^ to f rds inch. 
Messrs. Smith and Beck have introduced, during the past 
year, a new-pattern cheap microscope, called the " Popular 
Microscope.^^ The chief arrangements of this apparatus have 
been devised for the purpose of giving many of the advantages 
of higher class instruments at a reduced cost, and this object 
appears to have been gained. The mechanical stage adapted 
to it is very simple and flat. Two milled heads work con- 
centric spindles, as in Messrs. Powell and Lealand^s form. 
One of these spindles has a friction hold upon a plate which 
it carries up and down, while the second spindle pulls the 
first backwards and forwards horizontally, and the movable 
plate is so attached as to go with it. Thus, rectangular 
motions are very simply obtained. 
Considerable attention has been recently given to various 
forms of aquatic boxes for maintaining a continuous supply 
of fresh water to objects under constant observation, which 
thus sustain their vital growth for a long period. The employ- 
ment of these is strongly to be recommended, for there is yet 
much to be discovered concerning the metamorphoses which 
some of the lower microscopic forms of plant and animal life 
pass through, and a patient investigation will probably show 
that many which are now classed as distinct species are 
merely different phases of the same type, and which alternate 
in a higher or lower scale of development according to the 
varied conditions of temperature and nutrition under which 
they are grown. 
