206 
Proceedings of the Royal Society 
9. Notes from the Physical Laboratory of the University 
By Professor Tait. (With a Plate.) 
After passing through the usual routine work of acquiring skill 
in the fundamental operations, several of my students have re- 
mained long enough in the laboratory to make investigations in 
various branches of Physics. A great many of these inquiries 
related to matters already thoroughly known ; but some have 
claims to notice as dealing with subjects on which our information 
is as yet incomplete. These I propose, from time to time, to lay 
before the Society. Their value as scientific results must depend 
on the skill and care of the experimenters. For the forms of 
apparatus employed, and the mode of conducting the experiments, 
I am, in most cases, responsible. 
(1.) Mr J. P. Nichol has made a long series of experiments upon 
the Radiation and Convection of Heat, mainly to determine the 
amount of radiation in absolute measure, but incidentally with a 
view to finding how convection varies with the density of the air. 
The following is a preliminary notice of his work. The radiating 
body was a thin spherical shell of copper, filled with hot water. 
Its surface was sometimes bright, sometimes covered (by means of 
photographic varnish) with lamp-black. It was suspended by fine 
wires in a metallic vessel, which was blackened internally, fitted with 
a pressure-gauge, surrounded by cold water, and connected with an 
air-pump. An iron cup was let into the top of the shell, and con- 
tained a little mercury surrounding the bulb of a thermometer 
whose stem ascended in a glass tube which was inserted in the lid 
of the closed vessel. Considerable trouble was caused at first by 
the water leaking out of the shell when its temperature was high 
and the vacuum good — but in the later experiments this was 
entirely got over. 
As it was suspected that a difference of thickness of the lamp- 
black coating might influence the amount of radiation, the mode of 
experimenting finally adopted was to alter the air pressure in the 
vessel from time to time ; first, for instance, half an hour’s cooling 
at 100 mm , then half an hour at 200 mm , then at 100 mm , and so on. 
But the portions of the curves of cooling thus found on separate 
days fitted well together into a single continuous line, as is seen in 
