800 PROF. W. H. MILLER ON THE CONSTRUCTION OF THE NEW STANDARD POUND. 
and capable of being closed so as to be air-tight by a plate of glass E, 
smeared with lard. The tube PQ is graduated by lines traced upon the 
glass. The original tube, graduated in inches, having been broken, was 
replaced by a tube graduated in centimetres by M. Bunten. The sub- 
division is effected by an ivory scale S, of ten millimetres divided on the 
side next to the glass tube, to every fifth of a millimetre, attached to a 
rectangular rod of deal carrying frames on which filaments of silk TU, 
VW are stretched, and slips of brass having eye-holes so adjusted that 
the planes through the threads and the corresponding eye-holes may be 
perpendicular to the rod, the tubes being between the eye-holes and the 
Fig. 5. threads, as shown in the section fig. 5. A weak brass spring 
attached to the rod keeps it in contact with the tubes, with 
the silk threads and ivory scale close to that part of PQ 
which is graduated, so that it can be easily moved up and 
down, and is retained in the position in which it is left by 
the pressure of the spring. The support of the stereometer 
is adjusted by three foot screws till a thread of unspun silk by which a 
small weight is suspended, hangs coinciding with the axis of the tube DB. 
Within E is a cup in which is placed the solid the volume of which is 
sought. Mercury having been poured into D till its surface rises to P, 
the first division of the graduation, the mouth of the cup is closed so 
as to be air-tight by the plate of glass. The stopcock is then opened 
and the mercury allowed to escape till the difference of the altitude of 
the mercury in the two tubes is nearly equal to half the height of the 
mercury in the barometer at the time of the observation. Let the point 
M of the graduation mark the height of the mercury in PQ, and C the 
height of the mercury in DB. Let u be the volume of the air in the cup 
F before the solid was placed in it ; the volume of the solid ; b the 
altitude of the mercury in the barometer reduced to the temperature of 
the mercury in PQ and BD. Then 
5-MC 
Fig. 4. 
U — V- 
MC 
vol. PM. 
3 
13 
In order to find the capacity of the portion of the tube included between 
P and any point M in the graduation, the cup F is taken off’ and the 
stopcock L screwed into the iron collar N. The screw K is taken out, 
and the tubes placed vertical in an inverted position. The tube PQ is 
then filled up to about 50 cm with mercury poured through a slender 
glass tube inserted into the opening at K. This precaution is necessary 
in order to prevent the formation of air-bubbles on the inner surface of 
the tube, which would interfere with the correct estimation of the 
capacity of the tube. The stopcock is then opened, and the mercury contained in a 
