574 SPECIAL METHODS OF DISCOVERT. 



otherwise have been found. It was by means of much 

 more refined apparatus* that Fraunhofer, of Munich, was 

 enabled to observe and discover 576 dark lines in the solar 

 spectrum, although Wollaston, by means of the prism, had 

 previously found only seven. Airy also, by adopting a modi- 

 fied mode of observation, discovered that all the different 

 varieties of polarised light might be obtained by means of 

 rock-crystal, according to the direction in which the ray 

 was transmitted, and that a crystal of quartz is capable of 

 exhibiting every variety of elliptical polarisation of light. 



It was by the use of a more sensitive thermo-electric 

 pile than the original one of Seebeck, that Melloni was 

 enabled to make his discoveries in diathermancy. By 

 means of the very greatly increased delicacy of the 

 spectroscope as an instrument of chemical analysis over 

 that of previous chemical tests, Swan was enabled to 

 detect the widely diffused presence of excessively minute 

 quantities of common salt. 1 It was by the assistance also 

 of greatly increased sensitiveness of the galvanometer 

 which he employed, that Du Bois Keymond was enabled to 

 make his discoveries of electric currents in animal tissues. 

 As the molecular phenomena of nature are extremely 

 minute in comparison with the power of the senses, and we 

 are acquainted only with the more crude existences and 

 actions, it is probable that much of the discovery of the 

 future will be effected by means of still greater refinements 

 and powers of our apparatus and means of observation. 



c. By means of 'more intelligent and acute obser- 

 vation. Although this cannot be properly classed as a 

 different method, it is so common an occurrence that I 

 venture to place it under a separate heading. Many 

 discoveries have been made by attentively observing effects 

 which would otherwise have passed unnoticed ; for it is 

 1 See p. 3 79. 



