4) H. Kamerlingh Onnes and J. D. A. Books: Commun. Phys. Lab., Univ. Leiden No. 170b (1924) .
5) H. Kamerlingh Onnes and C. Braak: Commun. Phys. Lab., Univ. Leiden No. 99a (1907); H. Kamerlingh Onnes and C. Braak: No. 100a (1907); H. Kamerlingh Onnes and C. Braak: No. 100b (1907).