The President's Address. 
which means the luminosity of the reflected image was greatly 
increased, and a more equal illumination transmitted to each 
eye. 
The arrangement exhibited and recommended by the 
inventor does not differ materially in form and outline from 
his well-known form of binocular prism, and fits into the 
same space in the common double tube : the addition of 
another triangular prism in contact with the first reflecting 
surface allows direct rays to pass straight through into the 
eye-piece, while the others are reflected obliquely as usual. 
The plan is apparently simple ; but the objection raised against 
it is, that the difficulties of construction are so great that the 
inventor only is capable of making them. It is to be hoped 
that this assertion is unfounded. 
A somewhat different plan has been carried out by Mr. 
Ahrens, in which the principle of two combined reflections 
is still made available as in Mr. Wenham’s; but as the di- 
rect rays are thrown out of the axis, two new bodies would be 
required for its application. The several plans for obtaining 
the whole aperture in each eye so quickly following upon 
Messrs. Powell and Lealand’s arrangement, shows that an 
effect not depending upon a solitary condition may still afford 
ample scope for inventive ingenuity ; but it is candidly ad- 
mitted that combining an object with its own identically 
reflected image will give no stereoscopic relief, and conse- 
quently afford but little assistance in defining the projections 
and depressions of organic structure ; yet it remains to be 
proved whether in carrying the now habitual use of two eyes 
in observations with the low powers, on to the more trying- 
investigations with the highest, may not afford relief, and 
enable some observers to continue the use of the instrument 
beyond the time which sometimes compels them to lay aside 
the microscope, from the distress and injury to sight occa- 
sioned by employing one eye only for too long a period 
beyond its powers of endurance. 
Mr. Piper has brought before us an economical and 
convenient cardboard cabinet for objects, and a mode of 
making a slide with a movable cover for the preservation of 
objects which it is desired to view, without the interposition 
of a covering glass. It must be admitted that it is much 
better, when practicable, to examine objects as nearly as 
possible in their natural state, and these slides may assist in 
the preservation of many objects without the flattening and 
distortion incident to the usual mode of preparation. 
Mr. How has brought before us a useful and economical 
substitute for a mechanical stage, which he has attached to his 
