322 HISTORY OF MINERALOGY. 



of these secondary forms; the invention of a notation to express 

 them * the examination of the whole mineral kingdom in accordance 

 with these views ; the production of a work 8 in which they are 

 explained with singular clearness and vivacity ; are services by which 

 Hatty richly earned the admiration which has been bestowed upon 

 him. The wonderful copiousness and variety of the forms and laws 

 to which he was led, thoroughly exercised and nourished the spirit 

 of deduction and calculation which his discoveries excited in him. 

 The reader may form some conception of the extent of his labors, by 

 being told that the mere geometrical propositions which he found it 

 necessary to premise to his special descriptions, occupy a volume and 

 a half of his work ; that his diagrams are nearly a thousand in 

 number ; that in one single substance (calcspar) he has described 

 forty-seven varieties of form ; and that he has described one kind of 

 crystal (called by him fer sulfure jiarallelique) which has one hun- 

 dred and thirty-four faces. 



In the course of a long life, he examined, with considerable care, 

 all the forms he could procure of all kinds of mineral ; and the inter- 

 pretation which he gave of the laws of those forms was, in many cases, 

 fixed, by means of a name applied to the mineral in which the form 

 occurred ; thus, he introduced such names as equiaxe, metastatique, 

 unibinaire, perihexahedre, bisalterne, and others. It is not now de- 

 sirable to apply separate names to the different forms of the same 

 mineral species, but these terms answered the purpose, at the time, of 

 making the subjects of study more definite. A symbolical notation is 

 the more convenient mode of designating such forms, and such a 

 notation Haiiy invented ; but the symbols devised by him had many 

 inconveniences, and have since been superseded by the systems of 

 other crystallographers. 



Another of Hatty's leading merits was, as we have already intimated, 

 to have shown, more clearly than his predecessors had done, that the 

 crystalline angles of substances are a criterion of the substances ; and 

 that this is peculiarly true of the angles of cleavage ; that is, the 

 angles of those edges which are obtained by cleaving a crystal in two 

 different directions; a mode of division which the structure of many 

 kinds of crystals allowed him to execute in the most complete manner. 

 A.S an instance of the employment of this criterion, I may mention 

 his separation of the sulphates of baryta and strontia, which had 



Traite de Mineraloyie, 1801, 5 vols. 



