PHYSICAL RESEARCHES CONTINUED 79 



workers, and so to the teacher of science also ? The 

 workers in every laboratory are taught patient accuracy, 

 and so far so good ; but must we not encourage their free and 

 varied speculation as well ? Have not the great discoveries 

 been great dreams ? Are not Kepler's four laws the sur- 

 vivors of innumerable speculations some say hundreds, if 

 not thousands, of trials and guesses ? And did not Darwin 

 defend and recommend even ' fool-experiments/ as he called 

 them ? Many a new investigation has begun in this specu- 

 lative and tentative way. 



A further perspective is here of interest. At first it 

 seemed as if the discovery of ' touch/ or contact-sensi- 

 tiveness, in the field of electric radiation had no parallel in 

 that of optics ; but now we see it leading back from newly 

 observed phenomena of electricity to the interpretation of 

 those produced by light, and ultra-visible rays. The funda- 

 mental unity of the long spectrum is thus further manifested 

 and from one of its known extremes to the other, from 

 electric to photographic. 



By some instinct or foresight, Bose had already, in 1896, 

 when describing his receiving contact of the electric wave, 

 likened it to a ' photographic particle/ and that premonition 

 he was now able increasingly to substantiate. In a 

 paper which we have here no space to review ' The Con- 

 tinuity of the Effect of Light and Electric Radiation ' 1 

 it was investigated in many forms of matter, and further 

 generalised as well. Next, ' The Similarities between 

 Radiation and Mechanical Strains/ at first hypothetical, 

 were demonstrated experimentally, as by the construction 

 of a ' Strain-cell/ in which a sudden twist, through measured 

 angles, of one of two similar standard wires of any metal 

 immersed in water, was shown to produce a definite and 

 measurable amount of electro-motive force. The acted 

 wire usually behaves like the zinc plate of the ordinary cell, 

 but not always : some become copper-like. There are thus 

 two classes of bodies, much as we have seen for electric 



1 Proc. Roy. Soc., 1901. 



