546 



NATURE 



[December 22, 1921 



Dr. C. F. Marvin, chief of the U.S. Weather Bureau. 

 Referring to the action of gravity upon bodies moving 

 over a rotating globe, it is said to be expressed in 

 two wholly independent inertia reactions ; one, the 

 law of equal areas, is stated by the author to have 

 been fully recognised; the other action, though known, 

 is said never to have been christened, and its im- 

 portant part in controlling the motions of the air is 

 said to have been overlooked and misunderstood. Dr. 

 Marvin names this neglected principle the law of 

 the geoidal slope. Detailed quotations are given from 

 popular and mathematical writers, and their errors 

 are pointed out. The article concludes with a number 

 of categorical statements, giving important principles 

 which the motions of the atmosphere must satisfy. 

 This paper by Dr. Marvin formed the subject of the 

 discussion at the Meteorological Office at the first 

 lecture-meeting of this season, which was opened by 

 Sir Napier Shaw. A notice of the meeting at the 

 Meteorological Office and of the discussion on Dr. 

 Marvin's paper is given in the Meteorological Maga- 

 zine for November, and after a little criticism it sums 

 up with the following remark: "Although the points 

 brought out by Prof. Marvin are familiar to most 

 workers on dynamic meteorology, the publication of 

 the paper should call attention to the weak spot in 

 many text-books, and so improve the standard of 

 teaching the subject." 



When an electric current passes through a long 

 tube containing gas at a low pressure, one of the 

 most striking effects is the alternation of intensity of 

 light in the column of gas in contact with the posi- 

 tive electrode. The reasons for the alternations of 

 electric field on which the alternations of light depend 

 were stated in a general way by Sir J. J. Thomson 

 in his "Discharge of Electricity through Gases," 

 but in the December issue of the Philosophical Maga- 

 zine he gives these reasons a more definite and precise 

 form. By assuming that the current in the tube is 

 carried entirely by the electrons, he reduces the mathe. 

 matical difficulties considerably, and arrives at the 

 conclusion that when the pressure is less than a cer- 

 tain minimum determined by the nature of the gas 

 there will be at the end of the column nearest the 

 cathode periodic variations in the luminosity, which 

 will decrease in magnitude as the positive electrode is 

 approached, and that these variations will be super- 

 posed on a continuous luminosity. These conclusions 

 are in agreement with observation 



When running small electric motors it is neces- 

 sary, as a rule, to have resistances in the circuit at 

 the start which can be cut out when the speed of 

 the motor is sufficiently high. Bare resistance wires 

 are often used for this purpose, but as a rule they soon 

 become very brittle, and so have periodically to be 

 replaced. We recently had an opportunity of testing 

 two zenite resistances manufactured bv the Zenith 

 Manufacturing Co., of Willesden Green. They con- 

 sist of wires embedded in vitreous enamel. One of 

 them carried the rated current successfully for several 

 hours, but the other cracked slightly, the wire be- 

 coming exposed The makers state that the thermal 

 NO. 2721, VOL. 108] 



coefficients of expansion of the wire of the porce- 

 lain, and of the enamel in which it is embedded, are 

 the same. As a rule, however, the temperatures of j 

 the three substances will not be the same, and there- 

 fore there will be a tendency to crack. The zenite ' 

 units should prove very useful in a laboratory, as they 

 can be used for regulating the voltage applied to a 

 consuming device in an electric circuit. 



Vol. 14 of Contributions from the Jefferson Physical] 

 Laboratory and the Cruft Electrical Laboratory of: 

 Harvard University is a reprint of twenty-eight papers 

 issued from the laboratories during the years 1919 and 

 1920. They cover a wide field, and include twelve 

 on X-rays by Prof. W. Daune and his pupils, seven 

 on spectra (two of which are from Prof. Lyman), and] 

 six on apparatus for high pressure and the 

 properties of materials at such pressures by 

 Prof. Bridgman. Of the latter one of the 

 most important is that on the effect of pressure! 

 on the electrical resistivity of metals both in the 

 solid and liquid states, from which it appears that 

 the change of resistivity of a metal on melting follows] 

 the change of volume. The rate of increase of resis- 

 tivity with temperature is generally less for the liquid! 

 than for the solid, and normally the resistivity of] 

 solid and liquid decreases as the pressure increases. 

 Prof. Bridgman concludes from his work that the 

 amplitude of the atomic oscillation is the principal 

 factor in determining these changes of resistivity.j 

 and he puts forward a new theory of electrical conJ 

 ductivity in metals according. to which the electron! 

 of the older theories are not turned back by impact 

 with the atoms, but pass through the latter freely. 

 He shows that this theory reproduces the experimental 

 facts much better than any theory previously 

 advocated. 



In La Nature of November 12 M. Lemonon con- 

 tinues, and concludes, his articles on tidal power. 

 The present article illustrates and describes a number 

 of suggested methods of developing power by the 

 use of one or more tidal basins filled at high tide and 

 discharging through hydraulic turbines during the 

 falling tide. Such an installation developing 70 h.p. 

 for about five hours each day, situated at Saint- 

 Jouard-des-Guerets, on the Ranee, is illustrated. The 

 use of single- and double-basin systems is discussed, 

 and the barrage arrangements in a number of sug- 

 gested schemes are dealt with in some detail. The 

 article is purely descriptive, and does not attempt to 

 deal with the efficiency of the various methods out- 

 lined or with the financial and economic side of tidal- 

 power development. 



The National Research Council of the United States 

 has issued as its fourteenth bulletin a " General Sur- 

 vey of the Present Status of the Atomic Structure 

 Problem," by Profs. D. L. Webster and L. Page. 

 The former author has contributed a general account 

 of the phenomena, illustrated by diagrams, whilst 

 the latter has given the principal equations which 

 Bohr, Sommerfeld, and others have used in exploring 

 the problem of atomic dynamics. This survey will 

 be welcomed by readers who have not the time or 



