246 Scientific Intelligence. 



9. The Arc in Metallic Vapors in an Exhausted Space. — Dr. 

 E. Weintraub has conducted, in the laboratory of the General 

 Electric Company at Schenectady, an exhaustive series of experi- 

 ment on the Cooper-Hewitt mercury lamp. 



(1) By a series of experiments it was shown that in the process 

 of starting an arc the cathode plays an important role, so that a 

 certain change must take place on its surface before the arc can 

 start; the anode receives the current without any previous excita- 

 tion. 



(2) Starting from the recognition of this role of the cathode, a 

 new method has been devised for an instantaneous starting of the 

 passage of a moderate voltage current through the space separat- 

 ing the electrodes, and this no matter how long this space is. 



(3) The properties of the mercury arc have been studied, and 

 a number of differences in the behavior of the cathode and the 

 anode, beside the one mentioned above, stated. 



(4) The behavior of amalgams, as well as pure alkali metals, 

 has been investigated, and the complete analogy between the 

 behavior of the arc in their vapors and that of the mercury arc 

 shown. 



(5) Different ways have been found to cause an alternating 

 current to pass through mercury vapor in form of an arc. 



(6) On the basis of this a theoretically almost perfect rectifier 

 for conversion of alternating current into steady direct current 

 was developed. — Phil. Mag., Feb., 1904, pp. 95-124. j. t. 



10. Electricity and Magnetism. An Elementary Text-Book 

 Theoretical and Practical ; by R. T. Glazebkook. Pp. viii + 

 440. Cambridge, 1903 (The University Press). — This volume, 

 like the others by the same author in the Cambridge Phys- 

 ical series, is based on the first year work in physics as 

 given at the Cavendish laboratory. Also, like its prede- 

 cessors, it is a type of text-book little used in this country. 

 The ordinary method of carrying on instruction in physics is 

 threefold ; first, by means of a lecture course, second, by labora- 

 tory work, and third, by a quiz. As an aid to the two latter 

 branches, the common practice in this country is to provide the 

 student with two separate text-books — one treating the theory of 

 the subject from a general standpoint and the other containing 

 directions more or less minute for a certain number of experi- 

 ments. On the other hand, the English practice, as exemplified in 

 the book before us, is to combine the two books into one. That 

 this method has certain advantages in giving the student a better 

 perspective is obvious ; and that this view is coming to be more 

 appreciated here, is evidenced by the volume on Mechanics and 

 Heat which has recently appeared from the Ryerson laboratory 

 at Chicago. (See below.) 



The development of the doctrines of electricity and magne- 

 tism, together with their more important applications, is carried 

 out admirably along the lines which Maxwell made classic. The 

 experiments are well chosen and numerous examples are scattered 



