THE issue of the Journal of the Washington Academy of Sciences of June 15 contains the address of the retiring president of the Academy, Dr. F. B. Silsbee, of the Bureau of Standards, delivered in January. It extends to twenty pages, and deals with the additions which have been made during the last two or three years to our knowledge of the electrical properties of metals at very low temperatures. References are given to previous summaries up to 1935 and to nearly thirty memoirs on the subject which have been published since, most of them in 1936. The original description of a supraconductor as one in which the resistivity is zero is beginning to be replaced by the newer one that the magnetic induction is zero and that any current which flows in it is confined to an excessively thin layer at its surface. The abruptness of the change, of conductivity aa the temperature is lowered has been investigated, and in o the case of tantalum has been expressed by means of the error function. The paradox of how a magnetic field which cannot penetrate a supraconductor can still affect its conductivity is still unsolved, and the reasons for the decrease of heat conductivity and increase of specific heat in the supraconducting state have still to be determined.