164 Intelligence and Miscellaneous Articles. 



ments with moist carbonic acid ; here it is essentially rays which 

 belong to the visible part of the spectrum which show themselves 

 active. For if, to begin with, the ultra-violet light be shut off by 

 means of a glass plate placed before the lamp, we yet observe the 

 most marked difference if, by means of a board, a red or a green 

 glass, the more refrangible visible rays are taken away ; blue glass 

 allowed the active rays to pass to a large extent. That it cannot 

 be the heat-ray? which bring about the observed difference, is seen 

 from the fact that a plate of alum or a glass trough tilled with 

 alum-solution did not affect the action. It is to be remembered 

 that the kathode-rays are of different colours in carbonic acid and 

 in hydrogen. 



(7) From these experiments, and particularly from the fact that 

 it is exclusively the negative electricity which is influenced by the 

 light, we come to the conclusion that the above phenomena are 

 most intimately related to the production of the kathode-rays. The 

 conditions favourable to the development of the synchronously- 

 vibrating kathode-rays are facilitated by the light falling on the 

 electrodes, since their wave-length is different in different gases. 

 Different gases must be specially sensitive to the action of different 

 regions of the spectrum of different wave-length. The development 

 of the kathode-rays is further dependent, in a manner conditioned 

 by the individual peculiarity of the gas, upon the pressure ; so that 

 the magnitude of the influence which light striking the electrodes 

 can exert must also be dependent upon the pressure. The pheno- 

 menon we are considering may then probably be regarded as a kind 

 of resonance-phenomenon, somewhat similar to the bringing about 

 of an explosion by the detonation of certain definite substances only. 

 The kathode-rays, as it were, make the way clear for the succeeding 

 discharge. — Proc. of ilie Pliys.-Med. Inst, of Erlangen. 



SIR WILLIAM THOMSON S PAPER " ON THE APPLICATION OF THE 

 DECI-AMPERE OR CENTI-AMPERE BALANCE TO THE DETERMI- 

 NATION OF THE ELECTROMOTIVE FORCES OF VOLTAIC CELLS." 



On account of a numerical error in this paper (see Philoso- 

 phical Magazine for December 1 887), pointed out by Mr. Desmond 

 Fitzgerald in a communication to the 'Electrical Engineer' for 

 January 6, 1888, referring to Mr. Gray's measurement of Novem- 

 ber of the electromotive force of Clark cells constructed by Mr. 

 Bottomley last March, substitute for t he last four lines of the article 

 the following : — " correcting to 15° C . we obtain 1*4346 Eayleigh 

 volts at that temperature. This result is interesting as shoeing a 

 difference of less than -^~ per cen t. from that obtained by Lord 

 Eayleigh for similar cells, which was 1-435 at 15° C." 



