( 775 ) 



P — — 2.623 

 P 1= = 552.610 

 P s = — 1354.86. 

 The differences II' -//„ between the given values of p and those 

 calculated with these coefficients have been represented in (he last 

 column of table XV. They amount to little more than I atmosphere. 

 The results given in the table have been reproduced in a diagram 

 on PI. II 1 ); the curve traced there is the calculated parabola. 



It follows further from the values of the coefficients, that the 

 parabola cuts the ordinate p = in two points, where pvj is respec- 

 tively 0.00480 and 0.40307, from which follows with theformula') 



{pv A ) T = 0.99939 {1 + 0.0030618(7'— 273°.09)j 



for the corresponding temperatures measured on the absolute scale, 



2\ — 1°.3 r 8 =110°.2. 



The top of the parabola lies at a pressure of 53.73 at ins. the 



value of pvj is here 0.20394, from which follows, in connection with 



the value of — ; — I determined from the isotherms, viz. 



V dt y p =53.73 



0.0053, for the absolute temperature of the isotherm which passes 

 through the top that 



T — 63°.5. 8 ) 



Physics. — "On the measurement of very low temperatures. XIV. 

 Reduction of the readings of the hydrogen thermometer of 

 constant volume to the absolute scale." By Prof. H. Kamerlingh 

 Onnes and C. Braak. Communication N°. 97 6 from the Physical 

 Laboratory at Leiden. 



(Communicated in the meeting of Jan. 26, 1907). 



§ 1. Introduction. 



As it is till now difficult to obtain pure helium, and very 

 easy to obtain pure hydrogen (c.f. Comm. N°. 94/", June J 906), 

 the scale of the normal hydrogen thermometer (that with constant 

 volume under a pressure of 1000 m.M. of mercury at 0°) is for the 



a ) The temperatures have been given in absolute degrees below zero. The 

 temperatures noted down on the plate undergo slight alterations on account of a 

 more accurate calculation of the corrections to the absolute scale. They become 

 — 103°.54, -135°.07, -182°.75, -195°. 20, -204°.62, -212°.73 and -217°.32. 



2 ) This value of A ._ has been calculated from Schalkwijk's determinations of 



AU 



isotherms (cf. the conclusion of § 10). 



8 ) in this the corrections to the absolute scale have been taken into account. 



