. Le magazine philosophique; un journal de physique théorique, expérimentale et appliquée . tablethand devant la fente. L'exposition a duré une minute, lorsque le comprimé phosphorescent était à nouveau excité, et utilisé comme source de lumière comme avant. Après quarante excitations, la plaque photographique a été développée ; et une bande (illustrée en 11.) a été enregistrée, Avhich a absolument coïncidé avec la bande alreadyenregistrée dans le spectre visible. Il n'y avait pas de trace de longueur d'onde havino-anyradiation dans l'ultraviolet. WhetherThere est tout rayonnement en dessous du rouge est un point de moot, mais de la graduellement

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. The Philosophical magazine; a journal of theoretical, experimental and applied physics . tabletheld in front of the slit. The exposure lasted one minute, whenthe phosphorescent tablet was again excited, and used as asource of light as before. After forty such excitations the pho-tographic plate was developed ; and a band (shown in 11.) wasregistered, Avhich absolutely coincided with the band alreadyregistered in the visible spectrum. There was no trace of anyradiation havino- wave-lenoths in the ultra-violet. Whetherthere is any radiation below the red is a moot point; but fromthe gradually increasing brightness of the spectrum in theyellow, it seems probable that there is such. The next point to ascertain was the part of the spectrumwhich excited phosphorescence. A tablet similarly preparedwas exposed to the spectrum of the electric light, whichshowed carbon-bands strongly just above H, and also in theviolet near G. A sensitive photographic plate was placedin contact with the tablet, and allowed to remain in contact40 seconds, after which it was developed. Ill shows the. locality of the spectrum by which phosphorescence was ex-cited. This agreed absolutely with the visual observations.The exact locality was fixed by the carbon-bands above alludedto, and also by comparing it with a sensitive photographicplate exposed in the ordinary manner. It will be noticed thatthe ultra-violet rays do not seem to cause phosphorescence inthis case. It now remained to register those rays which destroy thephosphorescence. This was effected in the following manner:—A tablet was first excited, and after half a minute exposed to 214 JVotices respecting Neio Boohs. the spectrum : those rays which destroyed phosphorescencewere distinctly visible, as were also those which excited it.The tablet was placed in contact with a sensitive plate and de-veloped. The wave-lengths were determined by placing aliquid in front of the slit and noting the place where theknown absorption-bands in the

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