1876 .] Microscopy . 285 
cannot fail to have been struck with its brilliant definition : indeed the only 
drawbacks to its use have been its awkward form of mount and its great cost. 
The platyscopic lens admits of the same freedom in the manner of holding 
which makes the Coddington so convenient, while its freedom from chromatic 
and spherical aberration renders its definition vastly superior. Its working 
distance is also much greater than that of any lens of equal magnifying 
power: this is very perceptible in the smallest of the series, which gives so 
much space that opaque objects can be viewed with the greatest facility — an 
important matter to naturalists in field observations. The spines on the pollen 
of the Malvaceae are easily seen, and a very good view is obtained through a 
considerable depth of water. The performance of the lowest power is won. 
derful for so small an amplification, and, from its large field and long working 
distance, makes a good lens for dissection or other minute operations, espe- 
cially when mounted on a suitable stand. Owing to the perfect corrections of 
the platyscopic lens, the internal diaphragm made in the Coddington by 
grinding out the equatorial portion is not needed : the result is a vast increase 
in illuminating power, enabling the glass to work well in very bad lights. It 
is the most perfect single magnifier yet produced. 
The address of H. C. Sorby, F.R.S., President of the Royal Microscopical 
Society (Trans. Roy. Micr. Soc., Feb. 2, 1876) contains a vast amount of in- 
teresting matter. The limit of the power of the microscope is discussed at 
some length, and especial attention drawn to the difficulty of distinguishing 
true structure from interference fringes when the intervals between the real 
markings are of the same order of magnitude as half the length of the waves 
of light. This effeCt is altogether independent of the quality of lenses. It 
depends on the physical constitution of light itself, and would only be the 
more perfectly seen with more perfect objeCt-glasses. Some very intricate 
calculations are entered into with regard to the size of the ultimate atoms of 
matter. This part of the subject is too complicated to admit of an abstract. 
A careful perusal of the paper will repay those interested in so important a 
subject. 
The subject of Micro-photograohy has been brought before the Medical 
Microscopical Society by Mr. G. M. Giles. The principal novelty is the way 
in which the employment of the heliostat is dispensed with. This is effected 
by the use of a long focus condenser, giving an image of the sun of such di- 
mensions that it remains in field a sufficient time to permit of the object being 
photographed. The lens employed is an achromatic, photographic single 
combination, of 3J inches diameter, aud about 10 inches focal length. The 
microscope is inserted into a “ bellows ” camera, capable of being drawn out 
to a length of about 2 feet, and of a size to take plates 6 inches square. The 
mirror is about 4J inches square, is mounted so that its movements may be 
directed by means of cords running over grooved pulley : this is needed on 
account of the great length of the apparatus. The remainder of the fittings 
are of a kind that would suggest themselves to any practical photographer. 
Dr. M. H. Stiles, in an account of a method of staining and mounting wood 
sections, calls attention to a few points of manipulation which may prove of 
interest to microscopists. For softening dried specimens for cutting, a mixture 
of equal volumes of alcohol, glycerin, and water is recommended. For 
bleaching previously to staining, if required : — A solution of \ ounce of chloride 
of lime in a pint of water, shaking occasionally for an hour, and, after allowing 
the sediment to subside, decanting the clear solution. After pouring off the 
bleaching solution, wash the sections by soaking them for at least twelve hours 
in water, changing frequently, and finishing off with distilled or rain water. 
The elimination of the chlorine will be much facilitated by placing the sec- 
tions, after removal from the bleaching liquid, in a solution of hyposulphate 
of soda (1 drachm to 4 ounces of water) for an hour, and then washing as di- 
rected. Dr. Stiles, after staining, bleaching, and washing the sections, washes 
them three or four times with spirit, and, after draining, soaks them in oil of 
