KDomledge & Selentifie Neuis 



A AlOXTllLY JOURNAL Ul- SCILiNCE. 



Vol. I, No. 



[new series.] 



JUNE, 1904. 



r Entered at 

 LStationers' Hall 



] 



SIXPICNC 



Contents and IS'otices. — See Rage VII. 



RoLdio-Activity acrvd 

 R^aLdium. 



By W. A. SiiKNSTONE, I'.R.S. 



II. 



The discovery that radium gives ofT, unceasin'^ly, the 

 radiations discussed a little later, and the early observa- 

 tion that in many respects these resemble the Kiintgen 

 or X-rays naturally suggested that possibly a few 

 milligrams of radium miglit ad\antageously replace the 

 comparativelj' complicated equipment required for the 

 so-called X-ray photography, and accordingly this very 

 interesting side of the subject has excited some interest. 

 Whether radium rays will ever replace the usual 

 apparatus for the production of Rontgen rays remains to 

 be seen. But some very interesting results have un- 

 doubtedly been obtained, as my readers will gather from 

 the following series of very excellent radumi radio- 

 graphs which I am allowed to introduce by the kind 

 permission of Mrs. Gifford, of Chard, who has been 

 working on this subject with great success. The con- 

 ditions are given under each plate. Fifty milligrams of 

 highly-purified radium bromide in glass tubes were used. 



Fig 6 — The radium salt was enclosed in two light bags. Exposure, 

 24 hours, at a distance of 9-65 cm. Medium plate. Most of the 

 objects will explain themselves. The rectangular figures at the 

 top are produced by blocks of glass, that to the right by ura- 

 nium glass The crystal near the larger block was fluor spar, 

 the amorphous mass at the bottom on the reader's right is Kauri 

 gum. 



The trouble which arises in regard to the use of radium 

 salts for work of this kind, 1 am informed, is this : Thai 

 it is diflicult, if not impossible, to concentrate the acting 

 salt into a sufficiently small space. The radiations 

 used, in short, are too din'use. 



Fir,. 7. — Taken under much the same conditions as 6, but througli 

 a plate of aluminium and with a 10 hours' exposure. 



The distinctive characters of radium which were first 

 recognised were what are commonly known as " its 

 radiations." But almost more wonderful and mysterious 

 than these is the " emanation," which has been .so 

 carefully studied by Professor Rutherford, of Montreal. 



The Radiations of Radium. — These have been classified 

 as a, /3, and y ray.';. The last resemble Riintgen rays. 

 They are unaffected by a magnetic field, and are intensely 

 penetrative, passing through sheets of lead of consider- 

 able thickness, and these rays alone of the radium rays 

 can penetrate the eyelids freely, so that they can be 

 identified by the sense of diffuse light, of which one 

 becomes conscious when a few milligrams of a radium 

 salt are held near the tightly closed eye in a dark room. 



One of the greatest achievements in physics during the 

 latter half of the nineteenth century was the discovery, 

 by Prof. J. J. Thomson, of Cambridge, and his colleagues, 

 in the cathode stream of the Crookes* vacuum tube, 

 of particles so small that about 700 of them would be 

 required to produce a mass equal to that of an ;itom of 

 hydrogen. These particles carry negative charges of 

 electricity, and so are deflected by magnets; they will 

 pass through thin sheets of metal, cause damp, dust-free 

 air to form mist, and they make air conduct electricity. 

 They move with a velocity equal to one-tenth that of 

 light. They are often called " Electrons." * Now the 



• This terra was originally applied to the charge of electricity 



carried by an atom of hydrogen in electrolysis. 



