896 
have now come to the front a high degree of accuracy is desirable. 
In this respect it was an advantage: 1s* that particularly by the 
investigation of KAMERLINGH Onnes and Horst *) on the seales of the 
hydrogen and the helium constant volume thermometers we could 
avail ourselves of a more accurate temperature scale *); 2nd that the 
eryostats used at Leiden allowed the measurements to be performed 
under more favourable circumstances in other respects also. In fact 
in the measurements published in this paper an accuracy of 2 °/, 
has been reached at hydrogen temperatures, while there is reason 
to expect that in subsequent measurements the accuracy will still 
be considerably increased. F 
§ 2. Method. Apparatus. We followed with some modifications 
the method which has been in particular developed by Nernst and 
Eucken, and which has shown itself to be very suitable for low 
temperatures. In this method a block of the metal to be investigated, 
provided with wires for heating and temperature measurement, is. 
suspended in a vacuum which is made as perfect as possible. Within 
the block a measured quantity of heat is developed by an electric 
current, and the increase of temperature produced is measured. 
Fig. 1 represents the cryostat with the calorimeter. To protect 
the block against the residual heat radiation which enters the calori- 
meter vessel C’ (the vacuum-vessels are silvered a slit being left open), 
it is silvered on the outside up to a few mms. below the sealing- 
places C, of the platinum wires. Moreover the plate C,, which through 
a platinum wire is in heat conducting connection with the bath, 
prevents radiation from above. 
In the block B of the metal to be investigated a chamber has - 
been drilled, into which the core K fits tightly. This core contains 
the wires which serve for heating and for measuring the temperature ; 
when the temperature wire has once been calibrated and the heat 
capacity of the core measured separately, it can serve for the 
successive measurements of the specific heat of all the metals of 
of which suitable blocks can be made, and of other substances also 
when use is made of a suitable vessel. The core consists (Fig. 2) 
of a solid cylinder AK, and two cylindrical mantles A, and K,, all 
1) H. KAMERLINGH Onvnes and G. Hoist. Comm. No. 141a (May 1914). 
2) The temperature scale used by Nernst, and also those of EucKEN and 
Scawers and of Nernst and ScHWERS are mainly based upon the older cali- 
bration of the thermometer Pfy by KAMERLINGH ONNES, BRAAK and CLAY, which 
has to be replaced by the newer one of KAMERLINGH ONNEs and Horst. Cf. 
further § 3, 
