222 REPORTS ON INVESTIGATIONS AKD PROJECTS. 



PHYSICS. 



Batnett, S. J., Tulane University, New Orleans, Louisiana. Grant No. 149. 



For deterininhig ivhether an electric intensity is developed in a dielectric^ 



moving at right angles to a magnetic field. ( For previous reports see 



Year Book No. 3, p. 124, and Year Book No. 4, p. 245.) $250. 



Experimental work has been in progress for some time, and will, it is 



hoped, be completed before the end of the present academic year. 



Barus, Carl, Brown University, Providence, Rhode Island. Grant No. 292. 

 The ionization and nucleation of atmospheric air, natural and dust-free. 

 (For previous report see Year Book No. 4, pp. 246-247.) $1,000. 



The chief purpose of the volume recently submitted to the Institution for 

 publication is the development of the fog-chamber of simplest practical 

 character capacious enough to admit of the measurements of the largest 

 available coronas and efficient up to the highest exhaustions applicable — /. e. , 

 those which do not uselessly overstep the optical limits of the experiment 

 where fog particles become so fine as to be virtually inactive in diffracting 

 or scattering white light. This seems to have been accomplished, and the 

 results, so far as they go, are in no way inferior to the accomplishments of 

 Wilson's piston apparatus. It has not, however, been possible to go much 

 beyond the large green-blue-purple corona. The forms beyond are filmy 

 so and nearly colorless as to be unsuitable for measurement, but the steam jet 

 nevertheless reveals a whole order of axial reds, oranges, and yellows lying 

 beyond which have not been detected in any form of fog-chamber whatever. 



As used in most experiments, including the author's own earlier work, 

 the fog-chamber with plug stopcock seems to be of very inferior efficiency 

 as compared with the piston form. This, however, in a properly manipu- 

 lated apparatus is the case only when the attempt is made to measure the 

 drop in pressure isothermally at the fog-chamber, closed at once after exhaus- 

 tion. The datum must be computed from the initial pressures of the fog and 

 vacuum chambers, their final pressures when in contact (always at the same 

 temperature), and their volume ratio. Though some correction would be 

 anticipated, one would not be prepared for the large difference between the 

 apparent isothermal drop and the true drop as actually appears. In the 

 experiments of the volume the relation is fully 100 to 77, a difference of 

 nearly 25 per cent. Hence it will be necessary to restandardize the coronas 

 with this result in view, an undertaking in which the author is now engaged 

 and which the large number of other subsidiarj^ results that have since 

 accrued would alone have made desirable. 



Having improved the fog-chamber, it was made use of in certain incidental 

 experiments. The author has already shown that in case of the persistent 

 nuclei produced by intense X-radiation distribution of nuclei within the fog- 



