Trowbridge — Phosphorescence produced by Canal Rays, 141 



Art. XIX. —Phosphorescence Produced by the Canal Pays / 

 by John Tkowbridge.* 



In most cases the phosphorescence caused by the canal rays 

 is similar in color to that produced by the cathode rays. When, 

 however, the canal rays fall upon lithium chloride there seems 

 to be a marked difference. Professor 

 J. J. Thomson, in his treatise on con- 

 duction of electricity through gases, 

 describes a form of tube in which a 

 layer of lithium chloride can be bom- 

 barded alternately by both kinds of 

 rays, and he states that when the layer 

 is struck by the canal rays it shines 

 with a bright red light and the lines 

 of the lithium spectrum are very 

 bright ; when, however, the direction 

 of the discharge is reversed so that 

 the layer is struck by the cathode rays, 

 its color changes from bright red to 

 steely blue, giving only a faint contin- 

 uous spectrum but not the lithium 

 lines. The layer steadily becomes 

 black in hydrogen. 



I have succeeded in producing the 

 red phosphorescence by the cathode 

 rays, thus annihilating the distinction 

 in this case between the two kinds of 

 rays. The method adopted seems to 

 have a general application in the 

 study of phosphorescence and is as 

 follows ; 



The vacuum tube was of cylindri- 

 cal form; the cathode was a concave 

 aluminium mirror, the anode a circu- 

 lar iron electrode with a circular ori- 

 fice at its center. A glass tube was inserted in this orifice and 

 was welded to the walls of a tubular appendix, shutting out 

 all rays except those which passed through the orifice. This 

 cylindrical appendix 3 cm to 8 cm long was closed at the end by a 

 ground glass stopper with a flat end; on this end could be 

 sifted the layer of lithium chloride which was held by a suita- 

 ble medium ; a solenoid was slipped over the tube, the latter 

 forming the core of the solenoid ; the longitudinal magnetic 



* University Press, Cambridge, 1906, p. 642. , 



Am. Jour. Sci.— Fourth Series, Vol. XXV, No. 146.— February, 1908. 

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