1066 Mr. C. F. Bickerclike on the 



case of emission we conceive the centre as moving first, 

 dragging on the ends of the lines and sending flexures out- 

 wards. Conversely, when radiation is absorbed, flexures 

 travel inwards from the outer parts of the Faraday lines, and 

 the centre moves in accordance ; but that motion does not 

 itself produce an outward flexure so long as it is unopposed. 

 At all events, the kind and degree of such action must be 

 quite different from what it would be if the centre were 

 itself first acted upon independently of any pre-existing 

 motion of the lines. 



When, however, the electron comes up against the inertia 

 of a positive the situation is necessarily different. There 

 may be either reflexion or transmission. Prima facie one 

 would associate transmission with a state of things in which 

 there is no scope for free motion at all, and complete 

 reflexion with a state of things in which there are free 

 electrons which have already absorbed radiation up to a 

 critical point. 



The general nature of the argument may be illustrated by 

 a comparison with a vessel floating in water — notwithstanding 

 the fact that such analogies are liable to be very misleading. 

 A wave generated in the water moves the vessel up and 

 down — i. e. the vessel receives accelerations. We should be 

 very much in error, however, if we were to infer that these 

 accelerations in turn produce waves in the water in the same 

 degree and manner as if they were produced by some force 

 acting directly on the vessel and plunging it up and down in 

 water which was otherwise at rest. 



It is a different situation again, however, if the vessel is 

 tied by a string to a weight at the bottom of the water so 

 that it is not free to move in conformity with the wave ; but 

 whether that offers any useful analogy with the case of the 

 bound electron is difficult to say. We have to recollect that 

 the vessel is something existing independently of the water, 

 and substantially not affecting the state of the water, whereas 

 the electron really consists of lines which are presumably 

 states of the aether and not something existing independently. 

 We are not entitled to liken the lines to rods stretching out 

 from the vessel into the water, but not forming part of the 

 water. The analogy of a vessel in water has, however, the 

 limited use of calling attention to the importance of distin- 

 guishing between the conditions under which an acceleration 

 is produced as bearing on the effects to be inferred. 



If the suggestion is tenable that the perfectly free electron 

 will receive and absorb radiation up to some critical point 

 without emission at all so long as its motion is unhampered, 



