202 Professor Silvanus P. Thompson [May 8, 



Wiedemann,* and Lenarcl,t amongst the workers, to show what in- 

 terest has been concentrated on the subject. Hertz, whose loss science 

 has not ceased to lament, observed that a part at least of the kathode 

 rays were capable of passing through thin aluminium sheet, a pro- 

 perty which confirmed him in his previous doubt as to the material 

 nature of the kathodic discharge. His pupil, Philipp Leuard, now 

 Professor Lenard, of Aachen, took up the point. He fitted up a 

 tube with a small window of aluminium foil ojDposite the kathode, 



moving particles. He finds the kathode rays to consist of a heterogeneous variety 

 of kinds which differ from one another in their properties of causing phospho- 

 rescence, of being absorbed, and of being deflected by the magnet. On the Trans- 

 mission of the Kathode Kays through Tliin Layers of Metal, xlv. 28, 1892. 

 Hertz finds that glass fluoresces in kathode rays, even if covered with gold leaf 

 or thin films of various metals, though not if covered with thin mica. Aluminium 

 was found best, and allowed fluorescence to occur even when a sheet of aluminium 

 leaf was used so thick as to be opaque to light. A diaphragm of thin aluminium 

 leaf on a metal frame placed insi(ie a Crookes tube at 20 cm. from the kathode, 

 permitted enough rays to pass to give a tolerably bright and even fluorescence 

 over the whole of the further end of the tube. These rays, after passing through 

 the leaf of metal, still showed rectilinear propagation (with some diffusion) and 

 had not lost the property of being deflected by the magnet. 



* E. Wiedemann's papers which are of special importance have mostly 

 appeared in ' Wiedemann's Annaleu.' The following are the chief of them. 

 Some of the later have been written in collaboration with Prof. H. Ebert. 



On the Phosphorescent Light excited by Electric Discharges, Wied. Ann. ix. 

 157, 1880. 



On P^^lectric Discharges in Gases, xx. 756, 1881. 



On Fluorescence and Pho^^phorescence, Pt. I. xxxiv. 446, 1888. 



On the Mechanism of Luminosity, xxxvii. 177, 1889. 



On Kathodo- and Photo-Luminescence of Glasses, xxxviii. 488, 1889. 



On Electric Discharges in Gases and Flames, xxxv 209, 220, 234, 237, 255, 

 1888. 



On Electric Discharges, xxxvi. 643, 1889. 



On the Apparent Repulsion of Parallel Kathode Pays, xlvi. 158, 1892. 



On Electric Discharges; Excitation of Electric Oscillations and the Relation 

 of Discharge-tubes to the same, xlviii. 549, and xlix. 1, 1893. 



Researches on Electrodynamic Screening-Action and Electric Shadows, xlix. 

 32, 1893. 



Luminous Phenomena in Electrode-less rarefied Spaces under the Influence 

 of rapidly alternating Electric Fields, 1. 1, 221, 1893. 



With J. B. Mepserschmitt, on Fluorescence and Phosphorescence, Pt. II. 

 Validity of Talbot's Law, xxxiv. 463, 1888. 



With H. Ebert, on the Transparency of Kathode Deposits, Silzber. d. phys.- 

 med. Soc. zu Erlangen, Dec. 14, 1891. 



t Lenard's papers are : — 



Note on a Phosphoroscope, with spaik illumination, Wied. Ann. xxxiv. 918, 

 1888. 



With M. Wolf, Luminescence of Pyrogallic Acid, xxxiv. 918, 1888. 



With V. Klatt, on the Phosphorescence of Copper, Bismuth, and Manganese 

 in the Sulphides of Alkaline Earths, xxxviii. 90, 1889. 



On Kathode Rays in Gases at Atmospheric Pressure, and in the most extreme 

 vacuum, li. 225, 1894. 



On the Magnetic Deflexion of the Kathode Rays, lii. 22, 1894. 



On the Absorption of the Kathode Rays, Ivi. 255, 1S95. 



