March 26, 1915] 



SCIENCE 



467 



the electrodynamie theory of light in which the 

 author demonstrates the ascendency of Wil- 

 helm Weber over James Clerk Maxwell and 

 predicts that " the explanations furnished by 

 the electronic theory . . . contain the germs of 

 future progress in electric-light engineering." 

 The reasons for this prophecy, however, are 

 not disclosed. 



After explaining what an arc is, the condi- 

 tions under which it is formed and the 

 method of adjustment the author describes the 

 physical and chemical properties of ts^pical 

 electrode materials and the process of manu- 

 facture of carbon electrodes. This is followed 

 by a brief discussion of the theory of electrical 

 discharges based upon the electronic theory. 

 In the fifth chapter the author reviews some 

 of the investigations made upon spark dis- 

 charges between electrodes of different shapes 

 in air. The treatment of this subject seems 

 scant and antiquated in view of the many per- 

 tinent investigations made during the past ten 

 years. The effect of gas pressure, humidity, 

 temperature and kind of gas is not considered. 



The most valuable contributions to the subject 

 are made in the last three chapters. The sixth 

 chapter has to do with the voltage and current 

 conditions in the direct and alternating-cur- 

 rent carbon are lamp, the seventh with the dis- 

 tribution of energy in carbon arc lamps and 

 vapor tubes, and the eighth with the relation 

 between power and light emitted by plain and 

 mineralized carbon arc lamps and vapor tubes. 



The author confesses that some of his re- 

 marks are of purely didactic nature, and these 

 digressions, although prohibitive of smooth 

 development of the subject, contain many valu- 

 able suggestions. In expressing his disap- 

 proval of the term " watts per candle " the 

 author has anticipated the recent suggestion 

 of the term " lumens per watt." In remark- 

 ing that " physiological effects can no more 

 be expressed in mechanical horse-power than 

 can, for instance, Beethoven's ' Ninth Sym- 

 phony ' " it would seem, in view of the meas- 

 urements reported by our modern nutrition 

 laboratories, that the author might have chosen 

 a less vulnerable example. The text at times 

 seems to rise above the subject, the discussion 



in places being supported by cosmogonic reflec- 

 tions and the fourth dimension. 



R. G. Hudson 

 Massachusetts Institute of Technology 



SPECIAL ABTICLES 



LIGHT AND THE BATE OF GROWTH IN PLANTS 



A STUDY of the development of about a hun- 

 dred seed-plants in darkness in an equable 

 temperature chamber from 1900-03 in the 

 New York Botanical Garden gave foundation 

 for the following statement : 



The failure of a large proportion of tlie forms 

 examined to make an accelerated or exaggerated 

 growth when freed from the influence of light, 

 even when provided with an adequate food-supply, 

 shows that light has no invariable or universal 

 relation to increase in length, or thickness or to 

 the multiplication or increase in volume of sepa- 

 rate cells.i 



Precision appliances for the measurement 

 of illumination and of other environmental 

 conditions in daylight were not available at 

 that time, and it was therefore not possible tp 

 follow the contrasting reactions which ac- 

 companied illumination and shading of the 

 large plants which were the subjects in the 

 extended experiments. In one series, however, 

 the peduncles and scapes of Arisaema nearing 

 the end of their period of elongation showed 

 in initial acceleration when light was totally 

 excluded from the plants. This acceleration 

 reached its maximum in twenty-four hours 

 then decreased to a minimum equivalent to 

 the original rate in about four times this 

 period. The older plump assertion that " light 

 retards growth " continued to be cited without 

 modification by writers of text-books and com- 

 pendiums. The few investigators who turned 

 attention to the subject have been content with 

 referring to such cyclopedias. Thus Blaauw^ 

 says, in discussing positive and negative photo- 

 growth reactions: 



1 MacDougal, ' ' Influence of Light and Dark- 

 ness on Growth and Development," Mem. N. Y. 

 Bot. Garden, 2, pp. 307, 308, 1903. 



2 ' ' The Primary Photogrowth Eeaction and the 

 Cause of the Positive Phototropism in Fhycomy- 

 ces nitens," Kon. Akad. van Wetensch. te Amster- 

 dam. Proe. of meeting, January 31, 1914. 



