544 



SCIENCE. 



[N. S. Vol. XIX. No. 483. 



about .0002 cm. to .002 cm., according as fogs 

 of different degrees of fineness were precipi- 

 tated. The most highly graded nuclei, as 

 shown by the presence of fog particles of all 

 sizes, were obtained from an exposure of dust- 

 free air to the X-rays for from one to ten 

 minutes, depending on the intensity of radia- 

 tion. Much greater uniformity is shown in 

 the cases of phosphorus and ordinary air 

 nuclei. 



The author described a number of curious 

 phenomena observed with these water particles, 

 among which their continued motion when 

 caught on a film of liquid oil, simultaneously 

 to and fro between edges of the film, is most 

 noteworthy. Particles moving in swarms in 

 opposed directions are often in the focus of 

 the microscope together, and thus lie very 

 nearly in the same plane. The author 

 finally remarked that the coronal method had 

 now been so far perfected that the nucleation 

 increment produced by a single gas flame in 

 a moderately large lecture room could be de- 

 tected in about ten minutes, even in the air 

 collected from near the floor. This favorable 

 quantitative result may then be supplemented 

 qualitatively by the photographic method, 

 which will show the presence of exceptionally 

 small or large particles, whose effect vanishes 

 from the corona as they are relatively few in 

 number. 



Preliminary Measurements of the Short Wave- 

 lengths Discovered hy Schumann: Theodore 

 Lyman. 



The measurements were made with a con- 

 cave grating ruled on speculum metal, which 

 was found to reflect the extremely short waves 

 used in considerable intensity. All work was 

 carried on in an atmosphere of hydrogen and 

 at low pressures. Numerous lines were found 

 in the spectrum of hydrogen lying well be- 

 yond the aluminum group at 1,854. The 

 shortest wave-length thus far measured by Dr. 

 Lyman was 1,206 Angstrom tmits. This lies 

 far beyond the reg-ion where wave-lengths 

 have previously been measured. Dr. Lyman 

 is certainly to be congratulated upon the suc- 

 cess of these distinctly difiicult measurements. 

 The present communication is merely pre- 

 liminary. 



Tlie Hall Effect in the Electric Arc: C. D. 



Child. 



If two carbon pencils are so placed in an 

 arc that there is little or no potential differ- 

 ence between them, a potential difference is 

 produced by creating a magnetic field about 

 the arc. This may be as high as 1.5 volts. 

 It appears to be similar to the Hall effect in 

 metals, and if it is this effect, it would show 

 that the negative ions have a velocity enor- 

 mously greater than that of the positive. 



Salts placed in the arc which diminish the 

 drop of potential at the anode also diminish 

 the effect here studied. With KNO^ the 

 anode drop becomes as small as that at the 

 eatliode and the potential difference between 

 the two pencils became approximately zero. 

 When the pressure is reduced to about 1 cm. 

 the effect also disappears. 



No definite explanation of the phenomenon 

 can at present be given. It appears, however, 

 to be a more complicated effect than the 

 ordinary Hall effect in metals. 



Some Further Ohservations on the Radiation 

 Produced in an Alternating Condenser 

 Field: Fernando Sanford. 

 The author has continued the experiments 

 described in the December number of the 

 Physical Review, where it was found that 

 certain photographically active rays are given 

 off by a plate connected to the negative pole 

 of an induction coil, even when no visible 

 discharge occurs. It has now been found 

 possible to measure the wave-length of these 

 rays by means of a grating. Values are found 

 ranging from 350/j.//. to 377/^a, depending upon 

 the metal of the kathode. The rays, there- 

 fore, lie in the ultra-violet just beyond the 

 edge of the visible spectrum. 



Ernest Merritt. 



Secretary. 



THE geological SOCIETY OF WASHIXGTOX. 



The 151st meeting was held on February 

 10, 1904. 



A topographic model of Alaska made by Mr. 

 Edwin E. Howell was exhibited and was 

 briefly described by Mr. Alfred H. Brooks. 



This model of Alaska, which is to form a 

 part of the Geological Survey exhibit at the 



