PHYSICS — BARNETT, BARUS. 213 



PHYSICS. 



Barnett, S. J., Tulane University of Louisiana, New Orleans, Louisiana. 

 Grant No. 149. Investigation of the electric displacement and electric 

 intensities produced in insulators by their motion in a magnetic field. 

 (For previous reports see Year Books Nos. 3, 4, 5, and 6.) $250. 



The work abstracted in the last report, together with that accomplished 

 since, has been published.* The effect has now been studied with four 

 different insulators, and in all cases Lorentz's theory has been confirmed. 

 The effect in question could not be studied with some of the cylinders pre- 

 pared, for reasons given in the complete paper. In two cases the motional 

 e. m. f. under investigation was masked by a much larger e. m. f., radial in 

 direction, independent of the magnetic field, and proportional to the square of 

 the angular speed. While a true centrifugal differential displacement of the 

 oppositely charged constituents of matter, which this result would suggest, 

 doubtless exists, its theoretical magnitude, even on the most favorable hy- 

 pothesis in the case of conductors, is far less than the effect obtained would 

 indicate. And other important reasons exist for discarding such an interpre- 

 tation of the observations, for which no satisfactory explanation has been 

 found. Experiments on this effect and on the electromagnetic effect are to 

 be continued. The complete paper contains corrections of two erroneous 

 statements made in the abstract. 



Barus, Carl, Brown University, Providence, Rhode Island. Grant No. 505. 

 Study of the character of properties of condensation nuclei. (For 

 previous reports see Year Books Nos. 4 and 5.) $500. 



(i) During the earlier part of the year Dr. Barus continued his investiga- 

 tions on the nuclei of pure water with regard to their size and persistence. 

 These nuclei are obtained by the precipitation of water on the nuclei of 

 water-vapor, in a dust-free fog-chamber, by sudden cooling. The fog- 

 particles so obtained evaporate to water nuclei on compression, the number 

 of the latter as compared with the former being greater as the evaporation of 

 fog-particles is more rapid and as their size is larger. In the extreme case 

 nearly 50 per cent of the fog-particles were represented by these residual 

 water-nuclei. It was a curious observation that whereas the relatively enor- 

 mous fog-particles of pure water evaporate at once beyond the range of visi- 

 bility, such evaporation stops in cases of certain of the invisible water par- 

 ticles (0.5 to 50 per cent of the total number of fog-particles), as the evapo- 

 ration is more rapid in the manner specified. The remaining fog-particles 

 evaporate completely. It was impossible to detect any electrical effect due to 

 rapid evaporation. The cause of these phenomena is difficult to ascertain, 

 but it may be suspected that it is associated with the composite nature of the 

 molecule of liquid water. 



* Physical Review, November, 1908. 



