RECEPTION OF THE HAITIAN CRYSTALLOGRAPHY. 325 



was to mark the permanent additions he made to the science. His 

 system did, however, require completion and rectification in various 

 points ; and in speaking of the crystal lographers of the subsequent tim', 

 who may all be considered as the cultivators of the Hainan doctrines, 

 we must also consider what they did in correcting them. 



The three main points in which this improvement was needed were ; 

 a better determination of the crystalline forms of the special sub- 

 stances ; a more general and less arbitrary method of consider] HI-; 

 crystalline forms according to their symmetry ; and a detection of 

 more general conditions by which the crystalline angle is regulated. 

 The first of these processes may be considered as the natural sequel 

 of the Hauian epoch : the other two must be treated as separate steps 

 of discovery. 



When it appeared that the angle of natural or of cleavage faces 

 could be used to determine the differences of minerals, it became im- 

 portant to measure this angle with accuracy. Hauy's measurements 

 were found very inaccurate by many succeeding crystallographers : 

 Mohs says 1 that the}' are so generally inaccurate, that no confidence 

 can be placed in them. This was said, of course, according to the 

 'more rigorous notions of accuracy to which the establishment of Hauy's 

 system led. Among the persons who principally labored in ascertain- 

 ing, with precision, the crystalline angles of minerals, were several 

 Englishmen, especially Wollaston, Phillips, and Brooke. Wollaston, 

 by the invention of his Reflecting Goniometer, placed an entirely new 

 degree of accuracy within the reach of the crystallographer ; the angle 

 of two faces being, in this instrument, measured by means of the 

 reflected images of bright objects seen in them, so that the measure is 

 the more accurate the more minute the faces are. In the use of this 

 instrument, no one Avas more laborious and successful than William 

 Phillips, whose power of apprehending the most complex forms with 

 steadiness and clearness, led Wollaston to say that he had " a geome- 

 trical sense." Phillips published 1 a Treatise On Mineralogy, containing 

 a great collection of such determinations ; and Mr. Brooke, a crystal- 

 lographer of the same exact and careful school, has also published 

 several works of the same kind. The precise measurement of crys- 

 talline angles must be the familiar employment of all who study 

 crysta.lography ; and, therefore, any further enumeration of those 



1 Marx. p. 153 



