180 Britain's Heritage of Science 



now been brought to the period when men of the present time 

 were called upon to receive the heritage, and do their best 

 to hand it on to their successors. The problems of to-day 

 may not be seen in their right perspective; yet the last 

 thirty years have been so exceptionally fertile in new dis- 

 coveries that we may anticipate with confidence the judg- 

 ment of posterity on those great advances which have 

 revealed an entirely new class of phenomena, and enabled 

 us to form views on the structure of matter which, at any 

 rate, may be considered to be an advance on our previous 

 knowledge. A very brief summary, however, must suffice. 



In the seventies of last century it was generally thought 

 that our power to discover new experimental facts was 

 practically exhausted. Students were led to believe that 

 the main facts were all known, that the chance of any 

 new discovery being made by experiment was infinitely 

 small, and that, therefore, the work of the experimentalist 

 was confined to devising some means of deciding between 

 rival theories, or by improved methods of measurement 

 finding some small residual effect, which might add a more 

 or less important detail to an accepted theory. Though it 

 was acknowledged that some future Newton might discover 

 some relation between gravitation and electrical or other 

 physical phenomena, there was a general consensus of opinion 

 that none but a mathematician of the highest order could 

 hope to attain any success in that direction. Some open- 

 minded men like Maxwell, Stokes, and Balfour Stewart, 

 would, no doubt, have expressed themselves more cautiously, 

 but there is no doubt that ambitious students all over 

 the world were warned off untrodden fields of research, 

 as if they contained nothing but forbidden, though perhaps, 

 tempting, fruit. When Crookes, in the year 1874, constructed 

 his radiometer, it looked for a short time as if he had 

 definitely disposed of such timid and discouraging opinions; 

 but, on the contrary, he seemed only to have confirmed 

 them. For the apparent repulsion of light observed in the 

 radiometer was found to be due to the residual gas in his 

 exhausted vessels, and could be explained by the then 

 accepted kinetic theory. He had, no doubt, by greatly 

 improved methods, discovered a new effect, but this had 



