AS DETERMINED BY FIVE PLATINUM-RESISTANCE THERMOMETERS. 
243 
Temperature of Steam. 
Thermometer . 
1 . 
2 . 
3. 
4. 
5. 
1898, October 4 
„ 5 
101-286 
101-474 
101-610 
•589 
101-389 
•367 
101-179 
Adopted values 
101-29 
101-47 
101-60 
101-38 
101-18 
To those who have standardised naked platinum thermometers the discrepancies in 
the separate results for the b. p.’s of Nos. 3 and 4 may appear large. It should, 
however, be pointed out that it was necessary to standardise these instruments 
while they were sealed up in strong brass tubes with heavy leaden-covered leads 
attached ; hence it was impossible to eliminate altogether the effects of conduction 
along these tubes, but for reasons given on p. 244 it was not considered necessary to 
take further precaution against the small errors arising from this cause. In deter¬ 
mining the zero points the thermometers were placed in a trough 3 feet long, and 
any error arising from this cause was very much diminished. 
One of the most important considerations in connection with this subject is the 
degree of permanence in the fundamental points as determined at considerable 
intervals of time. It was the occurrence of discrepancies between the values which I 
found in my first observations and those determined about a year and a half 
previously at the time that the instruments were set up, which induced me to have 
all the thermometers exhumed and to make a thorough re-examination of the whole 
apparatus. This examination led eventually to my discarding the original leads, the 
insulation of which was found to fall off very much when they became damp. 
Another series of discrepancies was traced to an uncertainty in the contacts at 
the switchboard. In the original form the four steel prongs in which the fourfold 
lead from the resistance box terminates, were inserted into mercury cups into which 
also were led the four brass strips to which the thermometer leads were soldered. 
By having the steel prongs amalgamated, and adding springs to keep each prong 
firmly pressed against the brass strips immersed in the mercury, a great improvement 
was experienced ; and, since this change was effected, we have had no trouble from 
the same cause. It has been the habit, too, to make the observations from time to 
time with the four steel prongs in both positions, which affords a very satisfactory 
check on the character of the contacts. 
Taking advantage of a visit from Mr. Griffiths on October 6, 1899, I had 
thermometer No. 1 (6 inches) dug up, and we examined its zero point after exactly 
a year’s continuous observations. Determined in the same way as in the previous 
} r ear, the zero point of this thermometer was found to agree with the earlier value to 
less than 0 c- 005 C., the actual values being 
In 1898 ...... 0-306' 
and in 1899 .. 0’302 
2 i 2 
