904 REPORT— 1885. 
mented on steel containing manganese, and has obtained similar results. He has 
not, however, seen Dr. Hopkinson’s figures, and is unable to compare his own 
results with them. 
11. On the Cooling of Wires in Air and in Vacuum. 
By J. T. Bortomury, M.A., F.R.S.H. 
This paper gave a brief account of recent experiments on radiation of heat 
from the surface of metallic wires in air and in vacuum, A preliminary paper on 
this subject was communicated to the British Association at its meeting last year. 
Since that time the arrangements for experimenting have been greatly improved, 
and further results have been obtained. The object is to determine in absolute 
measure the loss of heat from the surface of small wires of various materials, both 
uncovered and covered with various coatings, the wires being surrounded with 
different gases at various pressures down to the very lowest. 
The chief experimenters on this subject in recent times have been Kundt and 
Warburg, and Mr. Crookes. My method of experimenting, which is very different 
from that of other experimenters, consists in passing a current of known strength 
through the wire under examination, and determining the increase in resistance of 
the wire due to heating of the currents when the wire has assumed a permanent 
temperature with the given current passing through it. When the temperature of 
the wire has become constant, the heat generated by the current (which can be 
calculated in absolute measure) must be equal to that emitted at the surface of the 
wire, plus that lost at the ends of the wire. The temperature of the wire at the 
moment is also ascertained from its resistance (as was done by Siemens in his 
experiments in resistance of platinum wire at different temperatures, ‘ Proc. R.S.’ 
vol. xix. p. 443); and the emissivity of the surface of the wire can thus be 
determined in absolute measure. 
My recent experiments have been directed to the determination of emissivities 
invery high vacuums. Using a Sprengel pump with five fall tubes, and a McLeod 
gauge of improved construction, due to Mr. C. H. Gimingham, I have obtained and 
measured a vacuum with air pressure as low as 4, M (one thirty millionth of an 
atmosphere). The wire with which I am experimenting at present is a platinum 
wire half a metre long and 0:04 c.m. in diameter. It is contained in a glass tube 
about 0°6 c.m. internal diameter. 
A table of emissibilities per metallic surface has not yet been completed, but 
one result obtained with a high vacuum may be quoted. On passing a current of 
1:18 amperes through this wire with full air pressure, the permanent temperature 
obtained by the wire was 75° C., the temperature of the room at the time being 
15:2 C. On exhausting down to 3, M (4 x 10-® atmosphere) and passing the same 
9 
current, the wire became heated to a good red heat. 
FRIDAY, SEPTEMBER 11, 
The following Papers and Reports were read :— 
1. On Kinetic Theories of Matter. 
By Professor A. Crum Brown, M.D., F.R.S. 
2. On Kinetic Theories. By Professor G. D. Livete, M.A., F.B.S. 
3. On Thermal Effusion and the Limiting Pressure in Polarised Gas. 
By G. Jounstone Stoney, LL.D., F.R.S. 
