160 Britain's Heritage of Science 



place must be given to Sir William Abney and Walter Noel 

 Hartley (1846-1913). 



The success of Manchester in establishing great research 

 schools encouraged other cities to introduce university 

 teaching into great manufacturing centres. But Man- 

 chester had a start of over twenty years, and its record is 

 necessarily greater for that reason alone. Nevertheless, some 

 of the younger universities soon attracted men of eminence, 

 and of these, two stand out prominently, Arthur Riicker 

 (1848-1915) and John Poynting (1852-1914), the first Pro- 

 fessors of Physics at Leeds and Birmingham respectively. 



Although Riicker was only connected with Leeds Univer- 

 sity during eleven years, much of his scientific work origi- 

 nated during that time ; and notably his researches on thin 

 films, carried on jointly with Professor Reinold. From the 

 colours of soap bubbles or of similar films their thickness 

 may be calculated, but as they thin out, the colour effects 

 disappear, and the film is black by reflected light. This 

 means that its thickness is less than the wave-length of 

 light and can not be measured by the simple optical method. 

 In order to investigate the molecular phenomena which 

 ultimately lead to the breaking of the film, Reinold and 

 Riicker undertook the extremely difficult task of measuring 

 the thicknesses of films when they are too thin for the 

 colour test to be applied. Their first method consisted in 

 determining the electric resistance of the films, the second 

 in increasing the number of films, until their aggregate 

 thickness became as great as the wave-length of light. 

 Both methods led to the same results, and some delicate 

 points in the subject of Molecular Physics were cleared up 

 by the investigation. 



It is not possible here to enter more fully into other 

 important researches of Riicker, which included the two great 

 magnetic surveys of the United Kingdom, carried out in 

 association with his friend, Sir Edward Thorpe. Riicker 

 was an organizer and administrator of the highest ability, 

 and left the mark of his activity on all the institutions with 

 which he was connected. In 1886 he was appointed Pro- 

 fessor of Physics at the Normal College of Science in London, 

 and in 1896 elected Secretary of the Royal Society; both 



