PROCEEDINGS OF THE SOCIETY* 
831 
objectives, using sunlight with an achromatic condenser in the axis. 
The inspection of these photographs reminded him that in discussing 
the production of such work recently with Mr. Comber, they were 
agreed upon the advantage of using sunlight, as compared with the oxy- 
hydrogen lamp, from the fact that when the image of the sun was focused 
on the object by a properly constructed achromatic condenser, the 
illumination was perfectly even over the whole field from centre to 
margin; but with the oxy-hydrogen light, focusing the illumination 
really resulted in the projection upon the object of an image of the 
incandescent spark and its immediate surroundings in the lime-cylinder, 
which image always consisted of a brightly luminous point encircled by 
a more or less mottled or cloudy appearance, representing the adjacent 
parts of the lime-cylinder that were not so highly luminous, on which 
the gas-jet was not so active. Doubtless, in the hands of a skilled 
manipulator the difficulties in the use of the oxy-hydrogen light were 
corrected as far as practicable ; still, there always remained an element 
of uncertainty in its use, demanding incessant watchfulness ; the light 
would vary in momentary intensity, or would flicker and become 
decentered, and the resulting photograph would embody not only an 
image of the object, but very frequently this would be mixed up with 
irregular mottled appearances which were in reality projections of the 
ever-varying condition of the source of light — the more or less incam 
descent parts of the lime-cylinder. The evenness of the solar illumination 
was well shown by Dr. Eoster’s photomicrographs, though he thought 
in some of them — notably in that of Surirella gemma , the condenser 
was not quite accurately centered. The greyness in some of them was 
probably due to errors in the photographic manipulations. 
Mr. G. F. Dowdeswell’s note on “ A Simple Form of Warm Stage ” 
was read, and the apparatus exhibited. It consisted of a thin, flat, quad- 
rangular plate of copper, having a projection of about 6 in. at one of the 
front corners ; an aperture was made in the centre to correspond with 
the aperture of the Microscope stage, and a copper tube was soldered 
across the surface near the back edge, in which a clinical thermometer 
could be inserted. In use the copper plate was to be clamped on the 
Microscope stage, and a spirit-lamp adjusted to heat the metal projection, 
and, by conduction, the preparation on the stage. 
Prof. C. Stewart inquired if the copper plate was intended to rest 
upon the metallic stage of the Microscope ? If so, he thought there was 
likely to be a considerable loss of heat by conduction. 
Mr. G. 0 . Karop said that a piece of flannel or cloth was usually 
placed between the two. He thought the great fault of all such things 
was that no means existed for controlling or maintaining the tempera- 
ture at any given point, so that when the observer was looking closely 
at some object of great interest he was very apt not to notice the rise 
of temperature, and the result was that it got so hot that the thermo- 
meter would break, to say nothing of what became of the object. 
What was wanted was a self-regulating warm stage, which would main- 
tain a given temperature, supplied at a price within the reach of tho 
bulk of medical students. 
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