414r Scientific Intelligence. 



point of obnllition of liquid helium is 4':{ absolute degrees. 

 When this value is corrected for jjropcr transference of helium 

 to the absolute scale, the point of ebullition will probably be 4-5. 

 The pressure at the triple ])oint is less tlian F'" of mercury. 

 According to corresponding states, the temperature corresponding 

 to the pressure of P'" is in the neighborhood of 3 absolute degrees 

 and, nevertheless, the liquid is still ])erfect]y mobile. Liquid 

 helium has a very low density, 0'15, which leads to a provisional 

 value of b of 0-0007. This gives for the critical pressure an 

 approximate value of 2 or '•\ atmospheres. At the point of normal 

 ebullition the ratio of the density of the vapor to that of the liquid 

 is in the neigliborhood of -^. This indicates a critical tempera- 

 ture hardly higher than 5 absolute degrees, and a critical 

 pressure a little greater than 2-3 atmospheres. The ])rovisional 

 value of the coefficient of pressure a is 0-00005, the smallest value 

 of a relative to different bodies, and lower than that of hydrogfen, 

 which for a long time was considered 0. — Communications from 

 the Physical Laboratory of Ley den. No. 108. j. t. 



6. Photoelectric Fatigue. — Dr. H. Stanley Allen reviews the 

 theories in regard to this fatigue and thus summarizes them : — 



(1) A chemical change, such as oxidation of the surface. 



(2) A physical change of the metal itself, as, for example, 

 roughening of the surface. 



(3) An electrical change in the formation of an electrical 

 double layer (Lenard). 



(4) A disintegration of the metal due to the expulsion of elec- 

 trons by light (Ramsay and Spencer). 



(5) A change in the surface film of gas or in the gas occluded 

 in the metal (Hallwacks). 



Dr. Allen concludes from his own experiments that we must 

 look to the gaseous films on the surface of the metals for the 

 explanalion of the chief effects of photoelectric fatigue. — Phil. 

 Mag., Oct. 1910, 564-573. j. t. 



7. A New Radiant JEm,ission from the Spark. — Professor R. 

 W. Wood shields the light of a spark from the eye by placing 

 the spark behind a vertical strip of metal. No illumination is 

 seen by the eye, but a photographic plate shows an actinic eflfect 

 in the air surrounding the spark. The emission is absorbed by 

 oxygen, and may be analogous to "Entladungsstrahlen." — Phil. 

 Mag., Oct. 1910, 707-712. j. t. 



8. Sterilization by Ultra- Violet Pays. — At first sight it would 

 seem that ultra-violet rays would be absorbed to so great an 

 extent by liquids that bacilli could not be reached at any 

 depth. A millimeter thickness of water absorbs completely 

 waves below 1800. M. Billon Dagueere, however, has discovered 

 that the ultra-violet rays exert remarkable sterilizing effect on 

 water. It seems possible that it may be a surface effect which is 

 transmitted from bacilli to bacilli, for the light certainly has little 

 penetrating power. The sterilizing action appears to be confined 

 to clear water ; impurities, suspended particles and colloids arrest 



