1824.] On the Crystalline Forms of Artificial Salts. 287 



to convince him, that the exceptions related solely to natural 

 planes ; for he would have perceived that I have said, " The 

 measurements obtained from planes produced by cleavage, may 

 be considered as approximating the truth much more nearly, 

 than those taken by means of the natural planes." And if the 

 Reviewer had condescended to peruse page xxix of the Intro- 

 duction, he would have found this remark ; " But if we cleave a 

 crystal, carbonate of lime for instance, if it be pure and transpa- 

 rent, we shall find, by the help of the reflective goniometer, that 

 the planes of the primary nucleus which will be extracted, meet 

 invariably under angles of 105° 5' and 74° 55'." The carbonate 

 of lime is here quoted as an instance, that if we cleave a crystal 

 [of any substance which is pure] the planes of cleavage will 

 meet under constant angles. 



I am now content to leave the reader and the Reviewer him- 

 self to judge whether he possesses or not the second and third 

 requisites for his office. I wish, however, that he may be dis- 

 posed to take these hints for his future government, and believe 

 the fact, that personal feeling is concerned in them only in so 

 far as belongs to the regret necessarily accompanying a mis- 

 statement of one's own words. It is for the credit and utility of 

 cleavage and the goniometer principally, that 1 am induced 

 thus publicly to expose the fallacies of a Reviewer whose 

 dicta on mineralogical systems ought to be received with 

 caution, since he has attributed to an author an error of his 

 own, and which if he had understood the science (he must excuse 

 me) could not have been written. 



It might not, perhaps, be very difficult to point out some 

 inaccuracies (to speak gently) in the Reviewer's review of the 

 Systems ; but with these I do not meddle. In line 21, p. 491, 

 there is, however, one error that must be noted for the benefit of 

 the Reviewer's reader. For brimstone read limestone. This 

 error is somewhat odd, considering the locality of its origin, and 

 must be ascribed to the printer, or rather one would think, to the 

 " printer's devil." 



Article XII. 



On the Crystalline Forms of Artificial Salts. 

 By H.J.Brooke, Esq. FRS. 



{Continued from p. 162.) 



Hydrate of Strontia. 



From the measurement and cleavage of some crystals of this 

 substance received from ihe laboratory of the Royal Institution, 

 I find its primary form to be a right square prism. The cleavage 



