560 SPECIAL METHODS OF DISCOVERY. 



enormous pressures, Hopkins, Bunsen, Sir W. Thomson, 

 Sorby, Mousson, and others made a number of discoveries 

 of the effects of those pressures upon the melting- and 

 freezing-points and solubilities of bodies. It was by sub- 

 jecting gases to enormous pressure and intense cold that 

 Cailletet liquefied nitrous oxide, and Pictet converted 

 oxygen and even hydrogen into liquids. It was by sub- 

 jecting all kinds of substances to extremely powerful 

 magnetism, that Faraday was enabled to discover many 

 new truths. A very great number of new experiments 

 remain to be made on the solubility of solids in liquids 

 and the electrolysis of liquids whilst subjected to enormous 

 pressure and cold ; also on the electrolysis of substances 

 in a fused state at very high temperatures. 



j. By employment of instruments of very greojt power. 

 This method is closely allied to, and may be considered as 

 included in, the one just described. By the employment 

 of very powerful presses, Hopkins, Mousson, and others 

 made various discoveries respecting the effects of enormous 

 pressure on the melting-points of solids and the solidify- 

 ing points of liquids. By means of very large solar lenses, 

 and also by using very powerful furnaces and blow-pipes, 

 some of the most refractory substances have been melted. 

 It was by the use of very large and powerful telescopes that 

 Sir J. and Sir W. Herschel and Lord Eosse were enabled to 

 make many of their astronomical discoveries, and found 

 that nebulae really existed, whilst some other celestial ap- 

 pearances, which were previously considered to be nebulae, 

 were found to be stars. ' By means of the Earl of Rosse's 

 telescope, the quantity of light that enters the human eye 

 from any part of the heavens, is increased something like 

 fifty thousand times.' 1 It was by employing a voltaic 



1 Whewell, Plurality of Worlds, p. 115. 



