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Aut. XVI . — Remarks on a paper by Mr Haidinger on the 
Crystalline form of the Sulphato-tri-carbonate of Lead . By 
H. T. Brooke, F. II. S. 
.A. N abstract of a paper by Mr Haidinger on the crystalline 
form of the Sulphato-tri-carbonate of Lead, was published at 
page 286. of the last Number of this Journal. The paper it- 
self has been printed in the Transactions of the Royal Society 
of Edinburgh. It will be seen from Mr Haidinger s statement, 
and from the other pages of this Journal to which he has refer- 
red, that I had supposed the primary form of this mineral to be 
a rhomboid ; that Dr Brewster had described some optical pro- 
perties belonging to it, which he conceived to be incompatible 
with that form ; that Mr Haidinger has imagined its primary 
form to be derived from an oblique rhombic prism ; and that 
three such prisms are asserted by Mr Haidinger to be combined 
in the production of those figures, which have the appearance of 
rhomboids, as seen in his figure 6, Plate X. Vol. X. of this 
Journal. 
Since the publication of Mr Haidinger’s memoir, I have a- 
gain particularly examined my own and several other specimens 
of this mineral ; and from the examination and the measure- 
ments of many different varieties of its crystals, I am satisfied, 
that Mr Haidinger has entirely mistaken its crystalline form, 
and that not one of his figures can ever occur among the crys- 
tals of Sulphato-tri-carbonate of Lead. By what accidental 
circumstance Mr Haidinger had been deceived, it is difficult to 
say, without seeing the specimens from which his notion of form 
has been derived ; but that he has been so deceived, may be easily 
ascertained, by any person who will merely take the trouble of 
looking at a few specimens of the mineral itself, and of measur- 
ing the mutual inclination of a few of its crystalline planes. It 
is not my intention to enter farther into the examination of Mr 
HaidingePs paper, than to shew that it must be incorrect, 
from the actual figure and measurements of the crystals which 
he has professed to be represented in his fig. 6. On comparing 
this figure with the corresponding one in the plate, published 
