THE PRESSURE DUE TO RADIATION. 117 



chtiracter of the gas action, which he found no way of eliminating 

 from his experiments. 



After Bartoli's work, the subject was dealt with theoretically by 

 Boltzmann," Galitzine,^ Guillaume,'" Heaviside,'' and more recently 

 Goldhammer,*^ Fitzgerald,'" Lebedew,^ and Hull''' have discussed the 

 ])earing of radiation pressure upon the Newtonian law of gravitation, 

 with special reference to the repulsion of comets' tails by the sun. 

 The theory of radiation pressure, combined with the known properties 

 in negative electrons, has recently been more or less speculatively 

 applied by Arrhenius* to the explanation of many cosmical and 

 terrestrial phenomena, among which the following may be mentioned: 

 The solar corona, zodiacal light, gegenschein, comets, origin of come- 

 tary and meteoric material in space, the emission of gaseous nebulas, 

 the peculiar changes observed in the nebula surrounding Nova Persei, 

 the northern lights, the variations in atmospheric electricity and ter- 

 restial magnetism and in the barometric pressure. Schwarzschild' 

 computed from radiation pressure on small spherical conductors the 

 size of bodies of unit density for which the ratio of radiation pressure 

 to gravitational attraction would be a maximum. 



Before the Congres international de Physique in IIMJO, Professor 

 Lebedew,^' of the University of Moscow, described an arangement of 

 apparatus which he was using at that time for the measurement of 

 light pressure. He sun)marizes the results already obtained as follows: 



Les resultats des mesures que j'ai faites jusqu'ici peuvent se resumer ainsi: L'ex- 

 perience montre qu'un faisceau lumineux incident exerce sur les surfaces planes 

 absorbantes et reflechissantes des pressions qui, aux erreurs pres d'observation, sont 

 egales aux valeurs calculees par Maxwell et Bartoli. 



No estimate of the "errors of observation" was given in the paper, 

 nor other numerical data. Unfortunatel}" the proceedings of the Paris 

 Congress did not reach the writers, nor any intimation of the methods 

 or results of Professor Lebedew\s work, until after the publication of 

 their own preliminary experiments. 



«L. Boltzmann, Wied. Ann. 22, 31, 291, 1884. 



&B. Galitzine, Wied. Ann., 47, 479, 1892. 



cCh. Ed. Guillaume, Arch, de Gen. (3), 31, 121, 1894. 



dO. Heaviside, Electromagnetic Theory, 1, 334. London, 1893. 



«D. A. Goldhammer, Ann. der Phys., 4, 834, 1901. 



/G. F. Fitzgerald, Proc. Roy. Soc. Dub., 1884. 



'JF. Lebedew, Wied. Ann., 45, 292, 1892; Astrophysical Journal, 14, 155, 1902. 



/'G. F. Hull, Trans. Astron. Soc. Toronto, p. 123, 1901. 



'8. A. Arrhenius, Lehrlnich der kosmischen Physik, Leipzig, 1903, pp. 149-158, 

 200-208, 226, 920-925. 



J K. Schwarzschild, Kgl. bayer. Akademie d. Wissenschaften, 31, 293, 1901. 



^"P. Lebedew, Ilai)ports presentes au Congres international de Physique (2), p. 

 133. Paris, 1900. 



