Chemistry and Physics. 81 



Kichards and his pupils, that tlie present edition has been made 

 necessary. 



The clear view that tins book gives of all atomic weight 

 investigations, and the impression given of the most laborious 

 calculations and the most painstaking conclusions, are its important 

 features. The author has followed his original plan of subject- 

 ing all the data, unless they are clearly defective, to a mathemati- 

 cal treatment according to their jjrobable errors. In this treat- 

 ment most of the older work has practically no influence upon 

 the final results, although in some instances older work seems to 

 have too great an effect upon modern work that is probably freer 

 from constant errors. It is probable that Dr. Clarke's method 

 must be abandoned eventually in favor of using only the most 

 accurate modern results in calculating the atomic weights, but 

 more work appears to be needed before this can be accomplished 

 satisfactorily. In any case the present work is most useful and 

 important. h. l, w. 



5. Pressure of Light on Gases. — Peter Lebedew calls atten- 

 tion to a paper by J. Kepler, "De Coraetis Augustae Vindeli- 

 corum, 1619," in which the author comes to the conclusion that 

 the repulsion of comets' tails by the sun is due to a pressure 

 exercised by the light rays. Lebedew also discusses a paper of 

 Fitzgerald, who working on Maxwell's well-known calculation of 

 light pressure, calculated the magnitnde of this pressure on the 

 supposition that each gas molecule behaved like an absolutely 

 black sphere under light pressure as black spheres of much 

 larger dimensions. Lebedew quotes recent investigators to show 

 that no restrictions are necessary to the theory that the gas 

 molecule behaves as an absolutely black body, and he proceeds to 

 measure the effect of light pressure, which Kepler was the first 

 to predict — which Maxwell calculated — which Lebedew showed 

 by investigation, and which Arrhenius has made the basis of a 

 wide generalization in cosmical physics. The results of Lebedew's 

 investigation are as follows : 



(1.) The existence of the pressure of light on gas is shown 

 experimentally. 



(2.) The pressures are directly proportional to the quantity of 

 energy impinging and to the absorption coefficients of the gas. 



(3.) Within the faults of observation B^tzgei'ald's contentions 

 are shown to be true. — Ann. der Physik, No. 1, 1910, jjp. 411- 

 43 "7. J. T. 



6. Coherers. — Dr. W. H. Eccles examines the subject of 

 coherers, mathematically and experimentally, and puts forward 

 the hypothesis that the properties of an oxide coherer " may 

 arise solely from the temperature variations caused in the minxite 

 mass of oxide at the contact by the electrical oscillations and by 

 the applied e.m.f. — Phil. Mag., June, 1910, pp. 869-888. 



J. T. 



7. Measurement of High Pressure. — The Reichanstalt at Char- 

 lottenburg continues its work on the measurement of pressure by 



Am. Jour. Sci. — Fourth Series, Vol. XXX, No. 175. — July, 1910. 

 6 



