( 939 ) 
supramarginalis. s.n.= substantia nigra. s.ol/f./.=stria olfactoria lateralis. s.s.t. = 
stratum sagittale internum. s.s.e. — stratum sagittale externum. 4 = sulcus temporalis 
superior. 71= gyrus temporalis superior. f = sulcus temporalis secundus, 711 = gyrus 
temporalis secundus. == sulcus temporalis tertius. 7i1= gyrus temporalis tertius, 
tap.=tapetum. fr.o.=tractus opticus V =ventriculis lateralis. v. @ As. = fasciculus 
Vicq-d Asyr. W = Wernicke’s field. 
Physics. — “The Rectilinear Diameter for Ovygen”. By B. Matitas 
and H. KAMERLINGH OnNES. Communication No. 117 from the 
Physical Laboratory of Leiden. 
(Communicated in the meeting of June 25, 1810 and January 28, 1911) !). 
§ 1. Introduction. As far back as Dec. 1894 the comparison of 
the equation of state for the permanent gases (particularly that for 
hydrogen) with the equation for ordinary normal substances was 
mentioned in Comm. N°. 14 dealing with the Leiden cryogenic Labora- 
tory as being one of the first objects for which efforts were made 
to develop the methods now used for obtaining accurate measurements 
at very low temperatures. While the law of corresponding states was 
assumed to be approximately correct for the group of substances of 
very low critical temperature as well as for the other normal substances, 
there were still reasons for suspecting that their reduced equations 
of state would show deviations on comparison with these of other 
substances greater than are found between various groups of ordinary 
normal substances. In fact, the reduced empirical equation of state for 
ordinary bodies differs considerably from the original reduced equation 
of VAN DER Waars; nor does this difference disappear when the 
equation is modified by making a calculation of the influence on the 
kinetic pressure of the finite dimensions of the molecules stricter than 
that developed by ascribing a constant value to 5. At that time the 
hope could be cherished that substances such as oxygen, nitrogen, 
and hydrogen would, on account of the simpler constitution of their 
molecules, show a better correspondence with the assumptions upon 
which vAN pER Waats based his caleulations, and that their reduced 
equations would approximate to the theoretical van per Waars 
equation, showing at the same time deviations from the reduced 
equations for the other substances. 
Operations intended to throw light upon this subject made but slow 
progress *). Cryostats had to be constructed that put a range of 
1) An excerpt from this paper appeared in the C.R. July and Aug. 1910. The 
Académie des Sciences at Paris has shown its greal interest in the study of the 
rectilinear diameter of liquids which exist at very low temperatures only, in granting 
one of us a subvention from the Bonaparte Fund so as to be able to come to 
Leiden. it is an agreeable duty to record our cordial thanks for this. 
2) See introduction to Comm. No. 974 (March 1907). 
