342 
PROFESSOR O. REYNOLDS AND MR. W. H. MOORBY 
heated by work, under the pressaie of the artificial atmosphere at pressure j), to 
maintain which it parts with some of the air, which, in passing out into the flexible 
pipe, carries out saturated steam, which is condensed by radiation from the pipe. 
The water, with the remainder of the air, is then carried by the centrifugal pressure 
into the outer chamber in the brake case under a pressure of about 50 inches of 
mercury. It then passes the automatic cock into the flexible pipe at 41 inches 
pressure, thence rising to the thermometer bulbs at 40 inches. In passing the 
automatic cock with a difference of pressure of 9 inches, the pressure will be further 
reduced, probably 9 inches below that in the pipe, so that any air that might have 
been retained would come out at that point, and expand further as it approached the 
thermometer bulb. 
In the fii'st instance, it was thought that a pressure of 5 feet of water would 
prevent the formation of bubbles, and the air gap in the l^ipe leading from the 
condenser was placed at this height above the thermometer. But many, and some¬ 
times large, bubbles of air were observed passing up the thermometer chamber; and 
Mr. JMoorby observed that he could detect the passage of a large bubble by a fall in 
the thermometer before the bubble appeared in the glass chamber. 
To prevent this, the air-gap was raised till it was 12 feet above the thermometer 
bulb ; so that the error is limited to three ten-thousandths. E\mn so, as it is much 
larger than any of the errors of constant sign, it was important to try, by assimilating 
the conditions under which the water leaves the brake, to obtain experimental 
evidence which would narrow the limits. 
It may appear at first sight as though these losses from the air in the water Avould, 
like the radiation, be eliminated in the difference of the large and small trials, but 
this is not so, since the quantity of heat so lost is proportional to the amount of water 
used, or it may be greater in the heavy trials. 
The Standard of Length. 
44. The measures of length that the research involves are — 
(1.) The horizontal distance of the centres of gravity of the adjustable loads on the 
brake from the axis of the shaft. 
(2.) The vertical heights of the barometer at which the boiling-points of the water 
were determined. 
In order to secure a definite reference of these to the British standard, recourse 
was had to two carefully-preserved and independent measures derived from this 
standard. 
(1.) A set of gauges by Sir Joseph Whitworth and Co., consisting of three steel 
bars, 9, 6, and 3 inches respective!}^, with parallel plane ends f inch in diameter, 
adapted to a 20,000 of an inch measuring machine, which constitute the standards 
used in the engineering laboratory. 
