14 THE NATURE AND ORIGIN OF LIFE 



latory movement of the ether that of a periodic oscil- 

 lation of its electro-magnetic state. However this may 

 be, the original formulae are still valid ; the model of vibra- 

 tory motion has not changed. 



In these vibratory movements of ether there is found a 

 series parallel to the series of sonorous vibrations although 

 entirely distinct from it, and infinitely more important. 

 This series has for its primitive nucleus all those luminous 

 radiations which form the spectrum of white light. It has 

 been increased by the discovery of the infra-red and ultra- 

 violet rays, and again by that of the X-rays in the order of 

 very rapid vibrations, and particularly, in the order of very 

 slow vibrations, by the discovery of the wonderful oscilla- 

 tions of Hertz (the Hertzian waves of wireless telegraphy), 

 which are like a tangible verification of Maxwell's theory. 



This series is not yet completely continuous ; certain 

 degrees in the scale are wanting to it, for example, at the 

 infra-red and ultra-violet ends ; but the wonderful continu- 

 ity which exists within the extent of visible spectra is a 

 pledge of future discoveries. 



It would be possible in an order of much larger phenomena, 

 to find the same model of periodic movements in the plane- 

 tary revolutions ; but this would scarcely interest us from 

 the point of view of the study of life, which has nothing to 

 do, at least directly, with the orbits of the stars. 



On the contrary, sound vibrations and light vibrations, 

 although they belong to two parallel series entirely distinct, 

 are very useful to us in locating life in nature ; for living 

 substances may be directly sensitive to these two orders of 

 vibrations. Animals see J and hear ; therefore the} 7 receive 

 impressions from phenomena belonging to two series so 



1 In unicellular animals without eyes wo study their sensitive- 

 ness to light under the name of " phototactism." 



