. The Becquerel rays and the properties of radium . out of the vessel, and theelectroscope is not discharged. In the case of the a-rays, it is only possible toproduce a very sUght curvature of the rays. Thusthe vessel at the bottom of which the radium is placedmust be made very narrow. It must consist of a mereslit between tvv^o parallel metal plates; for if the plateswere not very closethe rays could getout in spite of theirslight curvature. It is evident thatone such slit can-not give out verymuch radiation, onaccount of its nar-rowness. To getenough rays towork with con-veniently, it is ne-
. The Becquerel rays and the properties of radium . out of the vessel, and theelectroscope is not discharged. In the case of the a-rays, it is only possible toproduce a very sUght curvature of the rays. Thusthe vessel at the bottom of which the radium is placedmust be made very narrow. It must consist of a mereslit between tvv^o parallel metal plates; for if the plateswere not very closethe rays could getout in spite of theirslight curvature. It is evident thatone such slit can-not give out verymuch radiation, onaccount of its nar-rowness. To getenough rays towork with con-veniently, it is ne-cessary to have anumber of parallelslits, so that theradium is placedin a layer at thebottom of a boxcontaining a num-ber of parallelplates, with narrowspaces rays come through these narrow interspaces andenter the electroscope (fig. 17). It is necessary that the narrow slits should bereasonably long in order that the magnetic force mayact on the rays along a considerable length. Air,however, absorbs the a-rays very freely, and, if air. Outflow ofByOrcgen/ Fig. 17.—Eiitherfords arrangement for observing magneticdeviation of a-rays. The rays pass up between the metalslits, and enter the electroscope, causing discharge. Whena magnetic field is applied perpendicular to the paper, therays are curved, and can no longer get through the discharge is stopped. 74 THE BECQUEREL EAYS filled the spaces, practically no rays would getthrough. We cannot exhaust the entire apparatus,for the presence of some gas in the electroscope isnecessary to enable the rays to discharge; and wecannot exhaust the slits without exhausting theelectroscope, for it would be impracticable to make anair-tight partition thin enough to let the a-rays getthrough. The difficulty was got over by filling theapparatus with hydrogen, which is much less opaqueto the rays than air. The vessel with the series of slits was placedbetween the poles of a large and powerful electro-magnet, so that the li
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectradioac, bookyear1906
