in regard to Discoveries in Crystallography. 279 
der. From this time, I regularly employed the method in my 
lectures at Gratz, in place of the imperfect fragments I had 
hitherto been obliged to employ. Many persons, with whom I 
was in connexion at that time, are perfectly acquainted with all 
the particulars which I have just stated. I shall only mention, 
besides M. Haidinger, the Chevalier Thinnfeld, with whom you 
are likewise personally acquainted, Mr Riepl, Professor at the Po- 
lytechnical Institute at Vienna, and Professor Anker, my succes- 
sor in the chair at Gratz, all of whom I had at that time the plea- 
sure to rank among my pupils, and who will at all times be 
ready to bear testimony in the most decided manner to what I 
have advanced. 
Up to that period, the publications of Professor Weiss refer- 
ring to the present subject, had consisted only of the paper De 
indagando Formarum Cry st allinarum Characters Geometrico 
Principally and its continuation, printed at Leipsig 1809; two dis- 
sertations I never have seen, but in the form of a translation, which 
I met a considerable time afterwards in the Journal des Mines. 
M. Brochant de Villiers, the translator, has prefixed the con- 
tents of this memoir to his translation ; but he does not point 
out in it any of those connexions among the forms that might 
lead the reader to the notion of the real systems of crystallization ; 
he only mentions that the author, in order to express the geometri- 
cal character of some of the forms, has been forced to substitute 
others in their place, as, for instance, a rhombohedron in the 
place of the regular six-sided prism, and that this gave rise to 
several very interesting approximations. Such are, besides the 
one mentioned, that of the rectangular four-sided prism, with the 
isosceles four-sided pyramid (octahedron), and that of the ob- 
lique-angular four-sided prism, with a four-sided pyramid (octo- 
hedron) of an elongated basis. The latter of these, however, is a 
compound form as well as the prism, in the place of which it 
has been substituted. He also remarks, that M. Haiiy, too, had 
long ago shown the possibility of similar transmutations, and ef- 
fected them in several examples, and that Professor Weiss in 
this had proceeded from the very ideas and discoveries of M. 
Haiiy himself. 
Indeed, M. Haiiy has effected this transmutation in every 
case, where he employs for his primitive form any combination 
