242 Mr. William Phillips on the 



each substance may be most readily attained. Concluding that the 

 same difficulties are felt by others, I shall add some remarks on that 

 subject, in regard to such of the substances as I have been able to 

 cleave with regularity, presuming that it may tend to render the 

 way more easy for those who may desire to attain the same object. 

 It must be obvious that very different means have been resorted to; 

 for no one will imagine the same to be applicable to the sulphate 

 of barvtes and the sapphire : one of them soft, and yielding to 

 mechanical division with the utmost ease; the other, the hardest of 

 all the earthy minerals, and splitting only by the application of 

 great force, and even then, not without much difficulty and perse- 

 verance in more than one direction. Still further remarks will be 

 needful in regard to one of the substances, the sulphate of lead, 

 since the mechanical division it affords has necessarily led me to 

 differ from the Abbe Haiiy and the Count de Bournon, as to the 

 form of its primitive crystal. 



The following pages would not have been offered to the notice 

 of the Geological Society, but for such reasons as belong to the im- 

 portance of determining with precision not only the forms, but the 

 measurements of the angles of primitive crystals. If it should be 

 thought that it is assuming too much, to differ from authors so 

 distinguished as the Abbe Haiiy and the Count de Bournon, 1 beg 

 to offer the same apology as was offered by the latter for differing 

 from the former in the same respects. * The attainment of truth is 

 the great object that every man ought to propose to himself, who 

 has any pretension to science.' * 



Such of the figures in the accompanying drawing j" as suited my 

 purpose were copied from those of Haiiy, and when compelled to 

 a'ter the form, the letter by which he designates each plane, has 

 been studiously retained for the more ready reference to his works. 



* Catalogue, p. xvii. + PI. 12. 



