574 Scientific Intelligence. • 



in the various subjects. Consequently the topics are treated 

 from an entirely modern point of view. The articles are concise 

 and clear, and treat the subjects very satisfactorily for the use of 

 students. Usually some important historical points are given, as 

 well as some important statistics, but the articles are devoted 

 chiefly to clear descriptions of the processes and the principles 

 involved in them. The work is a very valuable one, and fur- 

 nishes the most useful information to those who are interested in 

 the development of applied chemistry and metallurgy. 



II. L. w. 



7. Ranmliche Intensitatsverteilung der X-Strahlen, die von 

 einer Platina nt ikuthode ausgehen. — The question of the distri- 

 bution of intensity of Rontgen rays has once more come to the 

 front as a consequence of the experimental demonstration, by 

 Barkla and others, of the polarization of these rays. According 

 to the pulse theory of X-rays the intensity should be greater at 

 right angles to the direction of the exciting cathode rays than 

 in a direction parallel to the latter ; also, the hardness should 

 increase with decreasing azimuth. The term " azimuth " is here 

 used to designate the angle which the axis of the cathode-ray 

 beam makes with the axis of the associated X-ray pencil. This 

 problem has been successfully attacked by W. Friedricij, who 

 used both photographic and electric methods of experimentation. 



The uncertainty arising from the inevitable variations in the 

 thickness of the glass walls of the focus tube was minimized by 

 affixing a little glass plate to the outside of the X-ray bulb at 

 each of the fourteen azimuths at which the intensities of the rays 

 were studied. These laminae were of such thickness as to com- 

 pensate for the inequalities of the walls of the Rontgen ray bulb. 

 Oiher investigators have attempted to eliminate this source of 

 error by theoretical calculations. For obvious reasons the author 

 used a platinum anticathode. In the photographic method the 

 X-ray pencils were separated from one another by suitable lead 

 screens so placed around the bulb as to allow only narrow wedges 

 of rays to fall upon the sensitized surface. In this way a series 

 of parallel "lines," corresponding to the various, azimuths, were 

 registered by the cylindrically folded photographic film. This 

 method possessed the great advantage of recording all of the im- 

 pressions simultaneously. The advantage thus gained was offset, 

 however, by our present ignorance of the law of photographic 

 blackening produced by Rontgen rays. In the electrical method 

 two condensers of special construction were employed. One con- 

 denser was kept fixed at a chosen standard azimuth, while the 

 other condenser was set successively at each of the remaining azi- 

 muths. The advantage of simultaneity was lost, but the errors 

 arising from this cause were minimized by repeating the obser- 

 vations a large number of times. On the other hand, the ioniza- 

 tion currents set up by the passage of the X-rays through the gas 

 in the condensers could be easily measured, so that definite quan- 

 titative results were obtained. In general, the photographic 



