June 30, 1916] 



SCIENCE 



937 



temporaries abroad are the degree of LL.D. 

 from the University of Glasgow in 1896, and 

 the Symons Gold Medal of the Royal Meteoro- 

 logical Society in 1912. 



Charles F. Brooks 

 Tale Univeksitt 



SPECIAL ARTICLES 



A NEW FORM OF PHOSPHOROSCOPEi 



Existing phosphoroscopes are of two types, 

 those with a periodically interrupted source of 

 light and those employing a steady source. 



To the first type belongs the classical instru- 

 ment of E. Becquerel,^ subsequently modified 

 by E. Wiedemann,^ in which the object is 

 placed between two parallel revolving disks 

 and is alternately illuminated and observed 

 through properly placed and adjustable open- 

 ings. 



In 1908 Merritt,* devised a phosphoroscope 

 in which the phosphorescent surface P, Eig. 

 1, was illuminated periodically by the passage 



of an opening in a revolving disk D mounted 

 between it and a source of light S. The phos- 

 phorescence was observed at the desired time 

 after exposure by means of a small revolving 

 mirror, M, mounted obliquely on the end of 

 the shaft. The disk was carried upon a hol- 

 low sleeve revolving with the shaft and the 

 angle between the opening in the disk and the 



1 A paper presented at the April meeting of the 

 American Physical Society, 1916. 



2 E. Becquerel, Annales de Chimie et de Phys- 

 ique (3), 55, p. 5, 1859. 



3 E. Wiedemann, Wiedemann's Annalen, 34, p. 

 446 (1888). 



* Nichols and Merritt, "Studies in Lumines- 

 ■cence, " Carnegie Institute of Washington, Publi- 

 •cation No. 152. 



plane of reflection of the mirror could be 

 varied during rotation. 



With this apparatus curves of decay of nu- 

 merous cases of phosphoreseence of short dura- 

 tion were determined by Messrs. Waggoner* 

 and Zeller.* 



In these phosphoroscopes, the source of light 

 is not in itself necessarily intermittent, the 

 periodic interruption of excitation being pro- 

 duced by the use of a revolving sectored disk. 

 Another group of instruments of this general 

 type employs the intermittent discharge from 

 an induction coil or transformer, as in the 

 spark-phosphoroscope briefly described by La- 

 borde in 1869,^ Crookes's device with sectored 

 disk and commutator for observing the after- 

 glow of substances subjected to kathode dis- 

 charge,^ Lenard's' phosphoroscope of 1892 and 

 de Watteville's^" apparatus for the spectro- 

 scopic study of phosphorescence (1906). Len- 

 ard's instrument differs from the others of 

 this group in that the eclipse of the exciting 

 spark is produced by the linear movement of 

 a screen mounted upon the plunger of a 

 Euhmkorff mercury interrupter in the pri- 

 mary circuit of the induction coil. 



The other type of phosphoroscope, in which 

 an uninterrupted source of light is used, like- 

 wise had its origin with Eecquerel.'^^ It was 

 later used for lecture demonstrations at the 

 Royal Institution by TyndalP- and for meas- 

 urements by Kester,*^ Waggoner^* and others. 

 It consists simply of a cylinder revolving on a 



5 0. W. Waggoner, Physical Beview (1), 

 XXVIL, p. 209. 



6 Carl Zeller, Physical Beview (1), XXX., p. 

 367. 



^ Laborde, Comptes Bendus, 68, p. 1,576. 



8 Grookes, Proc. of the Boyal Society, 42, p. Ill 

 (1887). 



9 Lenard, Wiedemann's Annalen, 46, p. 637. 



10 C. de Watteville, Comptes Bendus, 142, p. 

 1,078. 



11 E. Becquerel, Ann. de Chimie et de Physique 

 (3), 62, p. 5 (1861). 



12 See Lewis Wright, "Light," London, 1882, p. 

 152. 



13 Kester, Physical Beview (1), IX., p. 164. 



14 Waggoner, Publications of the Carnegie In- 

 stitution of Washington, No. 152, p. 120. 



