1179 
slightly higher high up in the cryostat, than half way down and 
below. We intend to check this result shortly by special measure- 
ments in the eryostat. But although thus there appears to be a small 
difference of temperature below and above, this causes but a very 
small inaccuracy in our density determinations. The middle of the 
resistance thermometers, which were mounted parallel to the dilato- 
meter, was about on a level with the middle of the dilatometer; 
hence the temperature indicated by the thermometers must be very 
near the mean temperature of the dilatometer and this is the essential 
quantity. 
For the reduction of the ‘noxious’ volumes the pressures were 
of course used as measured, without any correction. 
It may be mentioned that for the whole series of measurements 
no less than about 170 litres of liquid hydrogen and 400 litres of 
liquid air were required. 
§ 4. The calculations. For these we may again in many respects 
refer to previous communications. The reduction to the normal con- 
ditions of the gaseous volumes in the noxious spaces at low tempe- 
rature gave no difficulties, since the thermal behaviour of hydrogen 
at the temperatures and pressures of the experiments is accurately 
known '). It was a great convenience, that these measurements have 
been united in a special reduced equation of state for hydrogen 
VII. H,.3.*); by using the coefficients in this equation the various 
reductions could be accurately computed. 
The volumes of the hydrogen menisci were found by using pre- 
vious measurements in the Leiden laboratory concerning the capillary 
constants of hydrogen *). For the manner in which these calculations 
were made we refer chiefly to our paper on the diameter of argon. 
For the density of hydrogen under normal conditions, i.e. the 
mass of 1 litre of hydrogen at O° and 1 atmosphere Mortry’s value *) 
0.089873 was taken, which appeared to us to deserve most confidence. 
As regards the accuracy of our measurements it may be observed 
that 0.1 of a mm. on the tube of the dilatometer corresponded to 
an accuracy of the liquid volume of about '/,,,,; this accuracy 
1) H. KAMERLINGH ONNES and C. BRAAK, these Proceedings 9, p. 754; 10, 
p. 204, p. 413, Leiden Comm. Nrs. 97a, 99a, 100a. 
*) Published by J. P. DALTON, these Proceedings 11, p. 863, Leiden Comm. 
N° 109a. 
3) H. KAMERLINGH ONNES and H. A. Kuypers, these Proceedings 17, p. 528, 
Leiden Comm.°N®. 142d. 
*) E. W. Mortey, Zs. f. phys. Chemie 20 (1896), p. 68, 242, 417 and 
SMITHSONIAN Contr. to knowledge 1895. 
76* 
