358 CARNEGIE INSTITUTION OF WASHINGTON. 



atmosphere, but they have also shown that the intensity of this radiation is, 

 but about one-fourth as great as previously supposed. The origin of these 

 as yet mj'^sterious rays is being diligently sought by experiments now in 

 progress on Pike's Peak and in sounding-balloon flights which have already 

 been carried to nearly twice the altitudes reached by previous observers in 

 experiments of this kind. 



4. The photo-electric experiments of Nielson and Kazda have cleared up 

 former uncertainties as to the effects of surface films on the ejection of 

 electrons by light and have estabhshed with great definiteness and precision a 

 critical frequency at which any perfectly clean surface begins to be photo- 

 sensitive. These critical frequencies have been accurately determined for 

 aluminum, nickel, and mercury. The experiments bring out sharply the dis- 

 tinction between the electrical constants of a surface and those of the molecules 

 or atoms composing the surface and indicate the only method by which the 

 work necessary to remove an electron from a cold surface can be accurately 

 measured. 



5. Dr. Epstein has given the solution (now checked experimentally) of the 

 problem of the reflection of molecules, which had baffled physicists for fifty 

 years. These results are of much theoretical interest and they are also of some 

 practical value for the problem of the rate of settling of dust in the upper 

 atmosphere. 



6. Messrs. Milhkan and Bowen, in their work in the extreme ultra-violet 

 spectrum, have brought to light, and found the origins of, about 1,000 new 

 ultra-violet lines. They have shown that the exact positions of some of the 

 most important of these lines are predicted by the "Bohr" theory, and they 

 have found evidence that the strongest lines of the extreme ultra-violet 

 spectra of the elements from lithium to carbon are produced by atoms 

 which have been stripped of all of their valency electrons. This last result 

 is of much interest in its relation to the problem of atomic structure. 



Researches under way in the Norman Bridge Laboratory of Physics. 



1. Atomic radiations in the extreme ultra-violet. R. A. Millikan and I. S. Bowen. 



2. Measurement of the penetrating radiations of the upper air by sounding balloons. 



R. A. Millikan and I. S. Bowen. 



3. Attempt at reconciliation of the corpuscular and the wave theories of radiation. 



Harry Bateman. 



4. The mass of the electron in metals. R. C. Tolman and L. M. Mott-Smith. 



5. The new and very sensitive method of measuring the magnetic properties of gases and 



vapors. L. M. Mott-Smith and R. C. Tolman. 



6. Photo-effects and ionizing potentials at liquid air temperatures. R. C. Burt. 



7. The energy necessary to detach electrons from a clean mercury surface. C. B. Kazda. 



8. The change with the angle of emission of the energy of electrons ejected by light. 



E. C. Watson. 



9. Low voltage arcs and cumulative ionization. James B. Friauf. 



10. The precise evaluation of the ionizing potentials of neon and allied gases and vapors. 



H. K. Dunn. 



11. The penetration of atoms by low-speed electrons. R. C. Brode. 



12. The electrostatic field-strengths necessary to pull electrons from different metallic 



surfaces. R. A. Millikan and C. F. Eyring. 



13. Number of electrons detached from different atoms by shooting single alpha rays 



through them. R. A. Millikan and A. L. Greenlees. 



14. Energy of impact of positive particles necessary to detach electrons from metallic 



surfaces. A. L. Klein. 



15. Analysis of the atoms of very refractory substances for isotopes. A. H. Warner. 



16. Analysis of soft X-rays by magnetic-beta-ray method. J. A. Becker. 



