822 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Dr. Croolishank has, so far, been so satisfied with the oxyhydrogen light; 

 both for taking direct pictures and enlarging, that he has not deemed it 

 worth while to substitute any other. He more frequently employs it than 

 the paraffin lamp, partly on account of the diminished time in exposure, 

 especially when employing very high powers ; this is of great importance 

 where there is likely to be vibration from passing traffic. "With rapid 

 plates and the highest powers, the exposure has only been two or three 

 seconds, whereas, with the paraffin lamp, it may vary from three to ten 

 minutes, or even longer. 



The illuminating apparatus here shown consists of a lantern which not 

 only moves together with the Microscope on the central sliding-board, but 

 can be moved independently to or from the Microscope, and be clamped 

 with screws at the requisite distance for obtaining the best illnmination. 

 The lime cylinders should be of the best quality, of hard lime. Oxygen 

 should be supplied preferably in a compressed state in iron bottles. Not 

 only are the bottles much less cumbrous than the bags, but a small 

 quantity of gas can be used, and the residue left for an indefinite time, 

 and is always at hand to be turned on when required. On the other 

 hand, the retention of unused gas in the bags is liable to cause their 

 corrosion, owing to the impurities which are carried over in the manufacture 

 of the oxygen. 



A half-plate camera is employed, which is mounted upon a sliding 

 platform. This admits of the camera being pushed xip to the Microscope 

 when it is in the long axis of the apparatus, so as to make a light-tight 

 combination. The opening occupied in an ordinary camera by the lens, 

 can be shut off by means of an internal shutter, which is opened and closed 

 by turning a screw at the side of the camera. The dark-back is provided 

 with plate-carriers, so that either half, quarter, or lantern-size plates can 

 be employed. It is found convenient to have two or more dark-backs, so that 

 several plates may be exposed without re-arranging the light for each 

 exposure. 



Rafter's "Professional Photo-Micro-Camera."*— Mr. G. W. Eafter 

 criticizes a statement of the Hon. J. D. Cox that he obtained the best 

 results in photomicrography by using a No. 1 eye-piece in the Microscope 

 and no other amplifier. In his view the use of an eye-piece causes not only 

 great loss of light, but also great loss of distinctness in the image. He 

 also condemns the use of the Zeiss projection eye-pieces, on the ground 

 that " any process that necessitates the removal of one piece of apparatus 

 and the substitution of another in its place is for high-power work funda- 

 mentally defective," the inevitable disturbance of apparatus in making 

 such changes leading not only to loss of time, but usually to deterioration 

 of the negative. The author considers that the use of the simpler optical 

 combination of the adjustable achromatic amplifier for correcting micro- 

 scopic objectives when they are required to be used for projection is on 

 the whole preferable, and hence he included in a new camera which he 

 recently devised an arrangement for adjusting the amplifier so that the 

 best correction of the objective can be readily obtained. Aiter a very full 

 exposition of the optical principles involved, the camera is described as 

 follows : — 



" In order to get such ready means of adjusting the amplifier and to 



* Eafter, G. W., 'On the use of the Amplifier, With observations on the Theory 

 and Practice of Photomicrography, suggested by the design of a new Plioto-mif-ro- 

 camera,' sep. repr. from Rochester (N. Y.) OdontogrMphic JournRl, viii. (1887) pp. 110- 

 44 (14 figs.). 



