562 SPECIAL METHODS OF DISCOVERY. 



polarisation of light. Pliicker also, of Bonn, in the year 

 1847, by means of a powerful magnet, discovered various 

 effects of magnetism on crystals ; that their axes tend to 

 assume definite positions with regard to a magnet ; a 

 crystal with a single axis placing itself transversely to the 

 magnetism, as if repelled ; and one with two axes be- 

 having as if both axes were repelled ; also that this effect 

 was independent of the para- or dia-magnetic character of 

 the crystals ; and that it was simply a directive and not a 

 repulsive effect. 



Many investigators in succession, by gradually im- 

 proving the electro-dynamic induction coil during the 

 last twenty years, have so increased its power that electric 

 discharges in the cool atmosphere have been obtained, of 

 more than forty inches in length ; and much additional 

 knowledge has thus been obtained respecting the nature 

 and effects of electric discharge. By means of great 

 improvements in the power of magneto-electric machines, 

 investigators have been enabled to more completely 

 examine and discover new truths respecting the electric 

 light, the electric fusion of metals, &c. In microscopy, 

 spectrum analysis, and other subjects, a whole multitude 

 of discoveries have been made by means of powerful ap- 

 paratus, which could not have been effected without such 

 assistance ; and in every department of science, every in- 

 crease of power of the apparatus has been quickly followed 

 by new discoveries and an increase of knowledge, and the 

 foregoing are only a few instances selected out of the 

 great multitude of new truths which have been discovered 

 by the aid of this method. 



