240 MODEEIsr VIEWS ON MATTER. 



scattered * over the surface, coining and g'oing instantaneously, no 

 movement of translation l)eing seen. 



If a solid piece of a radium salt is ])rought near the screen, and the 

 surface examined with a pocket lens magnifying about 20 diameters, 

 scintillating spots are sparseh^ scattered over the surface. Bringing 

 the radium nearer the screen, the scintillations become more numerous 

 and brighter, until when close together the flashes follow so quickly 

 that tlie surface looks like a tur])ulent luminous sea. When the scin- 

 tillating points are few, there is no visible residual phosphorescence 

 and the successive sparks appear "atoms of intensest light," like stars 

 on a ])lack sky. What to the naked eye seems like a uniform "milky 

 wa}'," under the lens becomes a multitude of stellar points flashing 

 over the whole surface. 



"Poloiiiiun" l)asic nitrate, actinium, and radio-active platinum pro- 

 duce a similar efl'ect on the screen, but the scintillations are fewer. 

 In a vacuum the scintillations are as bright as in air, and, Iwing due 

 to interatomic motion, they are not afi^ected l)}- extremes of low tem- 

 perature; in liquid hydrogen the}' ai'e as brilliant as at the ordinarj" 

 temperature. 



A convenient way to show these scintillations is to flt the blende 

 screen at the end of a brass tube with a speck of radiimi salt in front 

 a))<)ut a millimeter ofl', and to have a lens at the other end. I propose 

 to call this little instrunuMit the *' Spinthariscope," from the Greek 

 word ffTrirfiapig^" a scintillation. 



It is ditficult to estimate the number of flashes of light per second. 

 With the radium about Ave centimeters ofl' the screen the flashes are 

 barely detectable, not more than one or two per second. As the dis- 

 tance of the radium diminishes, the flashes become more frequent, 

 imtil at one or two centimeters they are too numerous to count, 

 although it is evident this is not of an order of magnitude inconceivably 

 great. 



I*ractically the whole of the luminosity on the })lende screen, whether 

 duetto radium or ''polonium," is occasioned by emanations which will 

 not penetrate card. These are the emanations which cause the scintil- 

 lations, and the reasons why they are distinct on the blende and feeble 

 on the platino-cyanide screen is that with the latter the sparks are 

 seen on a luminous ground of general phosphorescence which renders 

 the eye less able to see the scintillations. 



« Et'Q ck vrjOi opovdEv avac,, SKO.e.pyo'; ^ AitoXXoov, 

 adrepi sidopfvo';, jusdoo r/jucxri rov 5' drco TroXXai 

 dTrivfjapiSsg Trooroovro, dsXai; 5' fzj ovpavbv Ikev' 

 (Here from the shi]) leaped the far-darting Apollo, like a star at midday, while 

 from him flitted scintillations of fire, and the brilliancy reached to heaven.) — 

 Homer's Hymn to Apollo, lines 440-442. 



