376 
MR. E. H. GRIFFITHS ON THE VALUE OF 
The steel chamber, together with the mercury, weighed nearly 2 cuTs. It stood on a 
small tripod in a galvanized iron tank, whose capacity was about 20 gallons. The tank 
itself was placed on a bed of Portland cement before the cement had hardened, and 
thus the whole erection was firm and stable. When the outer tank was filled, the 
surface of the water was about 3 inches above the lid of the steel chamber and was 
maintained at that level by a constant inflov^ of water, which entered almost above 
the screw Q and left by an overflow pipe shown at W. The screw at Q rotated in 
such a direction that the water was forced downwards, passed under the steel 
chamber, and returned across the lid. The screw revolved about 800 times a minute, 
and the stirring was very thorough, so that it was impossible to detect any difference 
of temperature in diflerent portions of the tank, even when hot water was being 
admitted, unless the thermometer was held immediately against the entrance pipe. 
A glass tube with narrow bore (Sprengel tubing) was fixed into the steel tube at D 
and communicated with the regulating apparatus shown in Plate 4, fig. 1. Rh the 
regulator—the gas entering at A and leaving at B. The tube R was about 1 inch in 
diameter and was drawn to a fine opening at its lower end. The thin glass partition 
C passed down the centre of this tube and projected at its lowest extremity into the 
narrow opening. To render the partition air-tight, its edges were coated with hard 
shellac, and after it had been thrust into position, the tube was warmed until the 
shellac melted. The top of the tube was closed with shellac, thus the gas, entering 
at A, could only arrive at B by passing round the lower end of this partition, and a 
very small movement of the mercury in the narrow neck sufficed to cut off the supply. 
We adopted this form of regulator after considerable experience of the ordinary fonn, 
in which the supply passes down an inner tube and up the annular space around it, 
which labours under the defect that the adhesion between the mercury and the 
inner tube causes the gas to remain cut off for some time after the mercury has com¬ 
menced to contract. The form here shown is free from this defect, as it is found that 
the mercury does not adhere to the thin glass partition. Beneath the narrow tube 
a small reservoir (capacity about 3 cub. centims.) at jE” allowed considerable contraction 
to take place, and yet permitted the mercury to be kept in view. A side tube passed 
from E to the three-way taps F and H, and thus, by means of the tap at F, mercury 
could be withdrawn when necessary. The tubes F[K and HL were about 4 feet 
in length —K terminating in a thistle-funnel, in which a supply of mercury was 
placed. 
The tube L was connected with the three-way tap M, by which communication 
could be made with the exhaust water-pump, or with the open air. Behind the tube 
L was fixed a vertical scale of millimeters, and the whole of the tubing was rather 
wide-bore Sprengel. Through the tap at H mercury from the arm KH could be 
passed into the arm KL to any convenient height. By means of the taps H and F 
any portion of this mercury could be passed into the regulator, and, if necessary, the 
same amount could at any time be withdrawn by connecting L with the exhaust (by 
