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SCIENCE 



[N. S. Vol. XXXVII. No. 958 



certaiiL definite velocity, should produce a j3-ray, 

 having now one velocity and now another. Several 

 attempts to explain this phenomenon have been 

 made, but without complete success. Doubtless 

 the true explanation must be sought for in the 

 internal structure of atoms, as in the first problem 

 mentioned above. 



The third problem I will mention has to do with 

 the 7-rays. It is known that the 7-rays are inti- 

 mately connected with the iS-rays, each type of ray 

 being capable of producing the other, but the 

 exact relationship between them is not very well 

 understood. The particular question, however, 

 that I wish to bring up is this: is the 7-ray a 

 wave form spreading out as sound waves do from 

 their source, or is it of corpuscular nature re- 

 sembling the sparks projected from an exploding 

 rocket? The fact that the velocity of the /3-ray, 

 which the 7-ray is capable of producing, does not 

 depend upon the distance from the source of the 

 7-ray to the point at which the /3-ray is produced 

 seems to indicate that the latter hypothesis is 

 correct. 



The explanations of these phenomena are inti- 

 mately connected with the theories of interaction 

 of matter and electricity, and it is interesting to 

 note that the theory, which in modern times has 

 been of most use, the theory according to which 

 both matter and electricity are of atomic nature, 

 was first promulgated about 150 years ago in our 

 own city of Philadelphia by no other than Benja- 

 min Franklin himself, the founder of this society. 



Perhaps the most important radioactive prob- 

 lem of practical value upon which scientists are 

 working to-day is the effect produced by the 

 various radiations on human tumors. Photographs 

 were shown illustrating the results obtained in 

 France and Germany by subjecting small super- 

 ficial cancers to the action of the rays. It must 

 be remembered that the problem of curing deep- 

 seated malignant tumors is by no means solved. 



Some Diffraction Phenomena; Superposed Fringes: 



Charles F. Beush, Ph.D., LL.D. 



Diffraction fringes, as usually seen, are not af- 

 fected by thickness or contour of a smooth, straight 

 diffracting edge, as pointed out by Fresnel. The 

 author finds, however, that when the fringes out- 

 side the shadow are observed within one or two 

 millimeters from the diffracting edge, by means of 

 a microscope, their brightness and sharpness are 

 very greatly affected by the character of the edge. 

 For instance, a cylindTical edge of several milli- 

 meters radius gives vastly brighter fringes than a 

 sharp razor edge. He finds this is due to super- 



position of many diffraction fringe patterns which 

 are nearly in register. They are believed to be 

 formed by many contiguous elements of the cyl- 

 indrical surface, each acting as a diffracting edge 

 and producing its own fringes. The author further 

 shows that the so-called ' '. single mirror interfer- 

 ence fringes ' ' of Lloyd may be produced under 

 conditions which preclude refiection, and which at 

 the same time make it obvious that they are 

 formed by superposition of diffraction fringes. 

 Matter in its Electrically Explosive State: Fran- 

 cis E. NiPHER, A.M., LL.D. 



New Investigations on Sesonance Spectra: K. 

 W. Wood, Ph.D. 



Application of Seoent Studies on the Origin of 

 the Earth's Magnetic Field to the Possible 

 Magnetic Fields of Rotating Bodies in General 

 (illustrated) : Louis A. Bauer, Ph.D. 



The Determination of Visual Stellar Magnitudes 

 by Photography : Edward C. Pickering, D.Sc, 

 LL.D., F.E.S. 



Ordinary photographic plates are most sensitive 

 to blue light, while the yellow rays are those that 

 affect the eye most strongly. Accordingly, blue 

 stars appear brighter and red stars fainter in a 

 photograph than to the eye. Isochromatie plates 

 are, however, manufactured which are very sensi- 

 tive to yellow light. If a yellow screen is inter- 

 posed the blue light is cut off and red stars appear 

 even brighter, relatively, than they do to the eye. 

 By using a thin yellow screen which cuts off only 

 a portion of the blue rays it is possible to obtain 

 plates having the same color index as the eye. 

 To fulfil this condition several blue and several 

 red stars have been selected near the North Pole. 

 Photographs are then taken with different screens 

 until one is found which gives images of the same 

 relative brightness as the naked eye. With the 

 16-inch Metcalf Telescope at Harvard, stars as 

 faint as the twelfth magnitude may be photo- 

 graphed in this way with an exposure of ten 

 minutes. With an exposure of two hours, stars 

 can be photographed about as faint as they can 

 be seen with a telescope of the same size. On a 

 perfectly clear night a photograph is taken of the 

 North Pole with exactly 10 minutes' exposure, 

 then similar exposures on four different regions, 

 then a second time on the North Pole, on five other 

 regions, and a third time on the North Pole. The 

 twelve plates are developed together and various 

 precautions taken to secure uniform results. The 

 magnitudes of numerous stars near the North Pole 

 have been measured with great care and the mag- 



