47-2 
1)1{. J. II. VIXCEXT (JX THE DEXSlTY AXD COEEFICIEXT 
I'lie funnel ^vus provided witli a sci'ewed collar, J, wliicli va.s permanently shrunk 
on to tlie cylindrical portion of its outer surface. This collar served to support a 
removable ring of iron, K. The walls of this ring (which we may call the mercury 
collar) were higher than the toj^ surface of D, when this latter was in position. The 
mercury collar ser^"ed two purposes ; it provided a means of sealing tlie whole of the 
top of the funnel l)y hooding Vvdth mercury when the closing plate D was in 230sition, 
the mercury it contained surrounded the bulb of the thei'inometer which was used 
to tind the tempei'ature of the contents of the funnel. When the funnel was not in 
position foi- the actual determinations of buoyancy, it could be held in a vice l)y the 
tlat surfaces cut in the thick metal at B. 
The vessel Avhich served to contain the water or ice, 'while it and its contents 
boated in tlie mercurv in the funnel, is shown in liy;. G. It was somewhat of an 
umbrella shape, and was cut out of a solid block of mild steel in the lathe. It was 
perfectly smooth, and provided no lurking places for air. The sides. L, were made of 
decreasing thickness downwards as also was the central stem, M, which was jiierced 
at its lower end witli a hole which served to attach the wire hy which the scale pan 
Avas supported. 
Steel wires of two diameters were used in the experiments—one, about '17 mm. in 
diameter, Avas used in the preliminary investigation of the dilatation of the umbrella, 
the other, about ’2 mm. in diameter, Avas used in the actual experiments Avhen 
the umbrella held ice or Avater. The Avire passed tlirough the mercury in the funnel, 
doAAui the centre of the tube, N, through the small hole in C, and had a specially 
constructed clamp attached to the end outside C. This clamp aa^is made so that 
Avhen held up close to the hole o hy the buoyancy of the umljrella and its contents, 
it coidd be enveloped by the screAved closed tidje, P (tig. 4). The clamp is shoAvn 
in tig. 7. The peculiarity in the construction of this clamp Avas that it aaus 
pierced by the holes Q and K, through Avhich the Avire passed as Avell as being held 
by tlie jaAvs. This arrangement made the cliance of the AAure slipping A^ery small. 
The course of the Avire is indicated by a broken line in tig. 7. The loAver portion ot 
the clanpj AA^as also drilled A\dth a screAved hole, S. This hole seiwed to receive a hook 
hy Avhicb the scale pan used to hold the Aveights in the equilibrations Avas supported, 
and was screAA'ed inside so as 'to enable the clamp to be attached to the piece C (tig. 4) 
ahvays at a definite distance by means of a second screAved piece Avhich could be 
attached to C. The object of this arrangement A\-as to ensure ahvays that the Avire 
AA'as tlie same length. 
In tig. 8 an iron cylindrical vessel is shoAvn in section. This reservoir could be put 
on the tube N (tig. 4), Avhich Avas made slightly conical at its loAA^er end in order to 
lit into the hole T. A bent Avire, U, Avas fixed into the side of the reservoir, and 
served to keep the stojiper, P, submerged AAdien the leservoir Avas full of mercury. The 
use ot this portion of the apparatus will be referred to in describing the process of 
filling the funnel A\dth pure, dry, air-free mercury. 
