1. Commun. Kamerlingh Onnes Lab., Leiden No. 108. § 6;Kamerlingh Onnes;Proc. roy. Acad. Amsterdam,1908
2. Commun. No. 119, § 4;Kamerlingh Onnes;Proc.,1911
3. Commun. No. 124b, § 1;Kamerlingh Onnes;Proc.,1912
4. Commun. No. 147b;Kamerlingh Onnes;Proc.,1915
5. Commun. No. 202b;Keesom;Proc,1929