( 1100 ) 
rise one can obtain an indication of the accuracy of the correction. 
For vapour density determinations the same dilatometer 4, was 
used but along with the volumenometer @; in this the gas was 
measured in a graduated tube, while it could be connected with A 
through Kag keeping Aa, closed. 
§ 4. Vapeur Pressures of Helium. The observed pressures have 
been corrected for the height of the helium surface above the middle 
of the thermometer reservoir 7/1’, for the aerostatical pressure be- 
tween the place where the pressure is measured and the surface of 
the liquid helium, and for the reduction of pressure due to friction 
along the coils of the regenerator spiral. In this way the following 
values were obtained : 
Helium, maximum pressure. 
Temperature 
760 7 
19 Pooer 
| II mean. 
5.01 565 
} 26 1.20 3.23 197 
2.31 2.40 Zeb ‚| 
1.47 1.49 1.48 3 
Columns I and Il refer to two independent measurements. 
In fig. 1 of Pl. I log. p & 760 (where p is expressed in atmos- 
1 
pberes) is graphed as a function of. At the same time the figure 
gives us an idea of the agreement with the van per Waats vapour 
p , Ti, BAE 
pressure law og. a =F (1 — 7). from which it would follow that 
ke / 
the curve should be a straight line. 
The curvature of the experimental curve is but small, but it is 
still clear that f decreases at the lower temperatures. 
If f is calculated from the tangent at 7’= 4.°29K. it is found 
that f=—1.2, T, = 5.°8K., while the two temperatures 4.°29 and 
3.°23 give f=11, T, = 5.°7 K. At lower temperatures f becomes 
