1882.] 
Notes . 
ng 
liar conditions under which the microscopic image is formed, 
very few persons have paid much attention to the subjedt. Like 
most old-established opinions, the dioptric theory of the micro- 
scopic image still holds its ground. It only needs the experi- 
ments to be seen to be convinced of the important bearings of 
Prof. Abbe’s discovery. A few hours spent in observing the 
wonderful influence the diffradtion spedtra have upon the magni- 
fied image will do more towards banishing the old erroneous 
ideas than the mere reading of many elaborate optical papers. 
No one can read the abstracts of Mr. Stephenson, Mr. Crisp, or 
the few pages devoted to the subjedt in the last edition of Car- 
penter on the Microscope, and at the same time carefully work 
through the simple experiments there described, without greatly 
adding to his knowledge of what seems at first a hopelessly ob- 
scure subjedl. For the purpose of examining the diffradtion 
spedtra in a more effectual manner than the usual way of re- 
moving the eye-piece and looking down the tube of the micro- 
scope, Mr. J. E. Ingpen, Secretary of the Quekett Microscopical 
Club, places a small “ Bamsden ” eye-piece, suitably mounted, 
over the ordinary eye-piece : by this means the ocular is con- 
verted into a small telescope, and permits the condition of the 
diffradtion spedtra which are formed just above the back lens of 
the objedtive to be readily observed. 
At the January meeting of the Royal Microscopical Society 
Mr. J. W. Stephenson gave the manipulative details of his pro- 
cess of mounting diatoms in phosphorus (“Journal of Science,” 
vol. iii., Third Series, 1880, p. 733). He also gave an account of 
another effedtive medium for mounting objedts to be examined 
with homogeneous immersion objectives. The new fluid consists 
of a saturated solution of biniodide of mercury in a saturated 
solution of iodide of potassium. The refractive index is i*68, 
giving a difference of visibility over balsam, in the case of dia- 
tomaceous silex of 0*14, and of air 0*54. The object is mounted 
by spinning a circle of white wax on a hot slide. This cell is 
filled with the medium, and the diatoms attached to the cover 
placed upon it ; a heated metal ring — e.g., an old gun-punch — is 
then pressed down in the cover to squeeze out the surplus fluid 
and melt the wax round the cover. After washing, to remove all 
traces of the solution, a few coats of gold-size will permanently 
secure the preparation. This medium possesses the advantage 
of being reduced to any refradtive index needed by dilution with 
water, and from its antiseptic properties would seem capable of 
preserving animal and vegetable tissues well ; of course time 
only can decide its properties in this respedt. 
M. A. Colson (“ Comptes Rendus ”) remarks that if disks of 
iron already partially carburetted are heated along with fresh 
disks, both absorb the same quantity of carbon if the diffusion 
of carbon in the metal is proportional to the duration of the 
