22 REPORT— 1898. 



the wave must fall upon it. Oliver Lodge has disproved this fallacy, 

 r^et the wave fall on a suitable receiver, such as a metallic wire or, better 

 still, on an arrangement of metal wings resembling a Hertz sender, and 

 1 he waves set up oscillating currents which may be led by wires (enclosed 

 in metal pipes) to the coherer. The coherer acts apparently by a species 

 < )f end-impact of the oscillatoiy current, and does not need to be attacked 

 in the flank by the waves tliemselves. This interesting method of 

 signalling — already developing in Marconi's hands into a successful 

 practical system which inevitably will be largely used in lighthouse and 

 marine work — presents more analogy to optical signals by flash-light than 

 to what is usually understood as electric telegraphy ; notwithstanding the 

 fact that an ordinary Morse instrument at one end responds to the move- 

 ments of a key at the other, or, as arranged by Alexander Muirhead, a 

 siphon recorder responds to an automatic transmitter at about the rate of 

 slow cable telegraphy. But although no apparent optical apparatus is 

 employed, it remains true that the impulse travels from sender to receiver 

 by essentially the same process as that which enables a flash of magnesium 

 powder to excite a distant eye. 



The phenomenon discovered by Zeeman, that a source of radiation is 

 afiected by a strong magnetic field in such a way that light of one re- 

 f rangibility becomes divided usually into three components, two of which 

 are displaced by diflraction analysis on either side of the mean position 

 and are oppositely polarised to the third or residual constituent, has been 

 examined by many observers in all countries. The phenomenon has been 

 subjected to photography Avith conspicuously successful results by Professor 

 T. Preston in Dublin and by Professor Michelson and Dr. Ames and 

 others in America. 



It appears that the difierent lines in the spectrum are differently 

 affected, some of them being tripled with different grades of relative 

 intensity, some douliled, some quadrupled, some sextupled, and some left 

 unchanged. Even the two components of the D lines are not similarly 

 influenced. Moreover, whereas the polarisation is usually such as to 

 indicate that motions of a negative ion or electron constitute the source 

 of light, a few lines are stated by the observers at Baltimore, who used 

 what they call the ' small ' grating of 5 inches width ruled with 65,000 

 lines, to be polarised in the reverse way. 



Further prosecution of these researches must lead to deeper insight 

 into molecular processes and the mode in which they affect the ether ; 

 indeed already valuable theoretic views have been promulgated by 

 H. A. Lorenz, J. Larmor, and G. F. Fitzgerald, on tlie lines of the 

 radiation theory of Dr. Johnstone Stoney ; and the connection of the 

 .new phenomena with the old magnetic rotation of Faraday is under 

 discussion. It is interesting to note that Faraday and a number of more 

 recent experimenters were led by theoretical considerations to look for 

 some such effiect ; and though the inadequate means at their disposal did 



