[WHEELER] THERMAL EXPANSION OF ROCK 27 
and 10 of 1-10th ohm. The ends of the bridge wire are soldered to 
German silver bands going around the ends of the cylinder and contact 
is made with these by means of German silver springs attached to the 
base-board. 
The connections are evident from the diagram. The 300 ohm coil 
will be seen to form part of the bridge wire. In place of C & C', which 
were originally cadmium cells, two Weston cells, furnished by Mr. A. N. 
Shaw of the Physics department were substituted as the standard of 
the E.M.F. The object of having two cells was simply that one might 
serve as a check on the other. The terminals R and R' were connected 
to a storage battery of which the E.M.F. remains practically constant 
for some little time, after balancing against the Weston cells by means of 
varying the amount of resistance in the circuit. 
R? and R° were connected to a galvonometer sensitive to less than a 
tenth of a bridge division; and R* and R’, to the long leads going to 
the thermo-junction. 
After the apparatus had been assembled, the calibration of the 
thermo-junction in connection with the Tory bridge was undertaken. 
The following table is a summary of the results of the various deter- 
minations which were made :— 





Point Determined. Divisions on Bridge Temperature. 
8 Wire. 
SOS SR ER Pls ONS occ rapes ayaa) ees 185.3 443 .4°C 
RENE OC ATEN PET 29.3 100.0 
SDS. her seule AU RE 186.5 444.6 
Winter alor re ee Re ee cts 2.3 15.2 
PS Rei gag EE ARE AR SEL. See 444.0 962.0 
AURAI UNE eee eee ee ae aia 272. (approx.) 657.0 
ADINUTN CUP MR NE | 274.6 657.0 
SIN AE Re PR SR EI UC 445.4 962.0 
SAUNA AE" eV 178.0 445.8 

In all these determinations, the thermo-junction was kept inside a 
porcelain tube. Considerable difficulty was experienced in the deter- 
mination of the sulphur point, it being practically certain that the 
sulphur vapour was superheated at first, as the sulphur point apparatus 
used is of the deep iron-cylinder form and it has been found that with 
this form of apparatus the vapour is very likely to be superheated. 
It seems possible that 178 bridge divisions even is a little too high. 
The metals were heated in a gas furnace until melted. Then the flame 
