Januaby 30, 1903.] 



SCIENCE. 



181 



ments used, which represented types from 

 all parts of the world. Mr. Bauer referred 

 especially to the satisfactory performance 

 of certain earth inductors, which were able 

 to give dip determinations with such accu- 

 racy as to readily show the diurnal varia- 

 tions. Mr. Bauer also gave a report of the 

 observations made at the time of the solar 

 eclipse in 1901 to detect the presence of 

 magnetic disturbances accompanying it. 

 Observations had been made at thirty dif- 

 ferent points distributed all over the world. 

 Unmistakable evidences of magnetic dis- 

 turbances were shown by the curves exhib- 

 ited, the maximum of the disturbance oc- 

 curring at the time of totality. Since the 

 time of totality was widely different at 

 different points, the effect observed could 

 not be due to disturbances of the ordinary 

 kind. 



Professor E. F. Nichols and G. F. Hull 

 presented a very interesting paper giving 

 the final results of their work on the ' Pres- 

 sure Due to Radiation.' Since their first 

 work on this subject alterations in the ap- 

 paratus had been made which permitted of 

 much greater accuracy in the results. The 

 pressure as computed from the observed 

 energy of the radiation used was found to 

 agree with the pressure actually observed 

 to within 1 per cent., the greatest variation 

 being 1.1 per cent, and the more usual vari- 

 ation being about 0.6 per cent. The effect 

 of wave-length on the pressure was tested 

 by using light which had been filtered 

 through a water cell or through red glass. 

 In each case the pressure was found to de- 

 pend upon the energy only, and no indica- 

 tion of any dependence upon wave-length 

 was observed. This is in accordance with 

 theory. 



In connection with this work the authors 

 also described an experiment by which 

 something greatly resembling a comet's 

 tail was obtained under conditions approx- 

 imating those of nature. A pow^der con- 



sisting of a mixture of emery and puff-ball 

 spores was placed in a vacuum tube con- 

 structed somewhat like an hour-glass. The 

 vacuum was made as perfect as could be 

 obtained, precautions being also used to get 

 rid of mercury vapor. Upon pouring the 

 powder from one part of the tube to 

 the other, and at the same time concen- 

 trating upon it the rays from an arc, the 

 lighter portions of the powder were seen to 

 be blown out as though repelled by the 

 light, and presented an appearance quite 

 similar to that of a comet's tail. The effect 

 was of the same order of magnitude as 

 would be expected from the authors ' values 

 for light pressure. The authors considered 

 it quite possible that the phenomena might 

 in part be due to other causes ; but even if 

 this is true the experiment reproduces the 

 behavior of a comet's tail with great accu- 

 racy. The apparatus used in measuring 

 light pressure and with the tube showing 

 the laboratory comet's tail were exhibited. 



Professor E. H. Hall gave a historical 

 account of the various' experiments that 

 have been made to detect a southerly de- 

 viation of a falling body, and described 

 recent experiments by himself on the same 

 subject. With suitable precautions to 

 avoid disturbances, nearly 1,000 balls had 

 been dropped through a distance of about 

 23 meters. The average deviation toward 

 the south was 0.05 mm. The results are 

 especially interesting, since the theory of 

 the subject as developed by Gauss and 

 others does not indicate that any deviation 

 should be expected, while most previous 

 experiments, like those of Professor Hall, 

 indicate a slight effect. 



The papers by J. R. Benton, viz., 'The 

 Elasticity of Copper and Iron at — 186° 

 C.,' 'Thermodynamic Formulas for Iso- 

 tropic Solids Subject to Tension' and 'Ex- 

 periments in Connection with Friction Be- 

 tween Solids and Liquids,' will have been 



