6 
PROFESSOR W. RAMSAY AND DR. S. YOUNG 
ture was apparently lowered 0“25° for a fall of pressure of 700 millims. The thermo¬ 
meter was next tested by a few determinations of the vapour-pressure of water. The 
water on the cotton-wool encasing the bulb having been frozen, pressure was raised to 
6 millims., and the melting-point of ice was observed. The mercury stood constant 
for a long time at —O’11. An apparent fall of temperature, due to reduction of 
pressure, of +0T9 — ( — 0Tl) = 0 - 3°, had thus occurred for a fall of pressure of 
754 millims., which agrees with sufficient accuracy with the former observation, 0'25°, 
for 700 millims. This change of zero-point was considered to be proportional to the 
pressure, and corrections introduced accordingly. A comparison of the vapour- 
pressures of water by our method gave results coincident with those of Regnauet 
up to 33°, and it was assumed that the graduation of the thermometer was equally 
regular below 0°. 
Vapour-pressures at Low Temperatures. 
Series I. 
Pressure. 
Temperature. 
Pressure. 
Temperature. 
millims. 
O 
millims. 
O 
73'65 
—17-73 
141-0 
-5-46 
74-15 
-17-68 
1527 
-3-90 
84-50 
-15-30 
153-85 
-3-73 
96-55 
-12-85 
168-9 
-1-81 
110-65 
-10-33 
184-05 
-0-11 
124-80 
- 7-94 
184 10 
-0-07 
139-85 
— 5"65 
186-05 
+ 0-13 
140-65 
- 5-55 
197-35 
+ 1-42 
Series II. 
Pressure. 
Temperature. 
Pressure. 
Temperature. 
millims. 
O 
millims. 
O 
79-95 
-16-24 
216-25 
+ 3-37 
105-45 
-11-23 
258-25 
733 
133-05 
- 6-74 
316-40 
11-96 
162-60 
- 2-71 
392-90 
17-19 
181-80 
- 0-33 
593-05 
27-64 
These results were plotted and a curve drawn through them. The pressures for 
each 5° between —15° and +5°, read from the curve, are as follows :— 
Temperature. 
Pressure. 
O 
millims. 
-15 
86-0 
-10 
112-3 
- 5 
144-8 
0 
184-9 
+ 5 
233-0 
