Intelligence and Miscellaneous Articles. 437 



2. The action o£ the rays is strictly unipolar ; positive electricity 

 is not carried away. 



3. The apparent charge of neutral bodies by the rays may prob- 

 ably be ascribed to the same cause. 



4. By far the. strongest action is possessed by rays of the 

 highest refrangibility (A. < 295 x 10 -6 millim.), which are wanting 

 in the sun's spectrum. 



5. It is necessary that the rays be absorbed by the surface of 

 the body ; the discharge is accordingly greater, the greater the 

 absorption. 



6. All metals are sensitive to this action ; some colouring-matters 

 (aniline colours) are the most sensitive. Water, which is trans- 

 parent for the active rays, was found to be insensitive. 



7. There is no appreciable interval of time between the moment 

 of illumination and the corresponding discharge. 



8. Other things being equal, the discharge is proportional to the 

 energy of the active rays, and of the illuminated surface. 



9. The action is perceptible even with very small densities ; its 

 magnitude depends on the density, and at first increases more 

 rapidly than the latter and afterwards more slowly. 



10. Two plates between which a difference of potential due to vol- 

 taic contact exists, represent a kind of voltaic element as long as 

 the electrically negative plate is illuminated by active rays. 



11. We are entitled to consider this actinoelectrical discharge 

 as an electrical current ;' the air (either by itself or by the action of 

 the particles mixed with it) plays the part of a bad conductor ; the 

 apparent resistance does not follow Ohm's law. 



12. The actinoelectric action is increased by the temperature. 



The author states in conclusion that the phenomena described 

 are only to be observed in gases. Experiments with solid and with 

 liquid insulators always gave a negative result. It follows from 

 this that actinoelectrical currents represent a kind of convection 

 current. (Compare the results of Bichat, Righi, Blondlot, Lenard, 

 and Wolff.) If it be assumed that at the boundary of metal and 

 air there is a difference of potential due to contact, then from the 

 discharge of the negatively electrical body, we may in some way 

 explain the charge of the feebly positively charged or neutral body. 

 Whether in this there is an electrolysis of gas (Arrhenius) or 

 not must be left an open question. 



Convection erplains only the further progress of the phenomenon ; 

 the first step of the electromotive excitation remains an enigma. 



The hypothesis of E. Wiedemann appears to the author very rich 

 in consequences ; but the inactivity of ordinary luminous rays (that 

 is, visible), as well as the decidedly unipolar character of the action, 

 is unintelligible. The analogy between the phenomena described 

 and the well-known discharges in Geissler's and Crookes's tubes is 

 striking. 



As regards the observations of Borgmann (see below), the author 

 Phil. Mag. S. 5. Vol. 30. No. 186. Nov. 1890. 2 H 



