Chemistry and Physics. 517 



was found that the potential gradient along the axis of the arc 

 was constant in all parts of the positive column and independent 

 of the length of this region. The potential-fall per centimeter 

 decreased hyperbolically as the current strength increased. The 

 anode and cathode drops were determined directly. The anode- 

 fall was independent of the length of the arc but decreased in 

 the interval between - l and 3 amperes from 150 to 30 volts, the 

 course of the curve being partly dependent upon the material of 

 the anode. The cathode-fall amounted to 20 volts and was inde- 

 pendent of the arc length and of the current. It depended very 

 slightly upon the nature of the cathode. 



Direct measurements of the cross-section of the arc in carbon 

 dioxide brought out the fact that the current density increased 

 linearly with the field strength. 



In the last part of the paper the author advances a theory to 

 account for the conductivity in the arc. It is based primarily on 

 the ionization produced by the collision of electrons whose 

 chaotic thermal velocity exceeds the inferior limit necessary for 

 ionization. By the addition of certain auxiliary hypotheses 

 regarding both the influence of radiation upon the conductivity 

 and the nature of recombination, the theory is developed suffi- 

 ciently to give the order of magnitude of the observed conduc- 

 tivity. Such details as the limiting of the cross-section of the 

 arc, the course and position of the characteristic in different gases, 

 •and the dependence of the characteristic upon pressure are 

 readily explained qualitatively on this theory. — Ann. d. Physik, 

 vol. xlvii, pp. 141-196, June, 1915. h. s. u. 



9. Prinzipien der Atomdynamik ; von Dr. J. Stai;k. Ill 

 Teil. Die Elektrizitat in chemischen Atom. Pp. xvi, 280, with 

 94 figures. Leipzig, 1915 (S. Hirzel). — As stated in the preface 

 to Part I (see this Journal, vol. xxxii, p. 67, 1911), the atomic 

 structure of matter would be the theme of the third and last 

 Part of the book. By the aid of his valence hypothesis concern- 

 ing the electrical structure of the surfaces of chemical atoms the 

 author has succeeded in correlating and accounting for a large 

 number of physical and chemical phenomena. A general idea of 

 the scope and contents of the present volume may be obtained 

 from the titles of the five chapters, which are: " Grundlagen 

 der chemischen Atomistik, Gleichgewicht der innermolekularen 

 Bindunsr, Reaktion der innermolekularen Bindung, Zwischen- 

 molekulare Bindung," and " Optik der Yalenzfelder chemischer 

 Atome." h. s. tr. 



10. Ten Years' 1 Work of a Mountain Observatory : by George 

 Ellery Hale. Pp. 99," 66 illustrations. Publication No. 235, 

 Carnegie Institution of Washington, 1915. — This little book con- 

 tains excellent photographs of the larger instruments which have 

 been installed in the Mount Wilson Solar Observatory and in the 

 associated physical laboratory at Pasadena, together with lucid, 

 concise accounts of the important results obtained with each type 

 of apparatus during the last decade. Good progress in the con- 



