486 
ON DK AWING CRY STAINS 
possibility for any person who is accustomed to accurate 
investigations. It is to a great extent the use of correct 
figures which has given Haiiy's crystallographic method 
that great superiority which it has always enjoyed over the 
Wernerian method, both in accuracy and elegance ; and to 
the study of Hauy*'s plates, far more than to the study of 
his writings, we must look as the point from which the sub- 
sequent labours of crystallographers started. 
By far the greater number of the figures in the first edi- 
tion of Haiiy'^s TratU are executed with care, and according 
to the best method which could possibly have been adopted- 
Since the appearance of that work, most of the authors of 
crystallographic publications have followed the same plan, 
while others have more or less deviated from it. Many of 
the figures contained in the works of the present day, it 
must be owned, are much inferior to Haiiy's, in point of 
correctness. It is, however, but very lately, that an intro- 
duction to a method of projections has been thought wor- 
thy to receive a place in systematic works on crystallogra- 
phy, and of these I shall only mention here the Traite de 
CrijstaUograph'ie by Abbe Haiiy, and the Introduction to 
Crystallography by Mr Brooke. The graphic method, 
which it is the object of this paper to develop, is that fol- 
lowed by Professor Mobs ; it is equally distinguished by the 
easiness in its application, and the accuracy of which it is 
susceptible. 
A useful representation of a crystal must contain every 
thing remarkable and requisite, for identifying it with the 
original in nature. Its chief object is, therefore, to express 
the relative position of the faces, and consequently the pa- 
rallelism of those edges, which are parallel in the crystals 
themselves. This object can only be attained, if we sup- 
pose the eye of the observer to be at an infinite distance 
from the soUd which is to be represented, in order to have 
