159 
on the SulpJiato-tri-carbonate of Lead. 
mens on which the crystals purported to be represented by fig, 
6. occur, he will observe, that they do not exhibit the slight- 
est trace of salient angles upon the terminal planes, or upon the 
cleavage planes parallel to these, or of re-entering ones upon the 
lateral planes b ; but that both the terminal and lateral planes 
are distinctly single , and frequently very brilliant, particularly 
in those crystals which are the most symmetrically formed, and 
where , on account of their symmetry , Mr Haidinger's imagi- 
nary lines ought to be the more apparent. If, after having in- 
spected these crystals, the reader will measure them by the re- 
flective goniometer, he will find, when the planes are bright, 
that a on h will measure 90°, and the planes b on each other 
120°, or within a very few minutes of these angles. I have found 
on one crystal a on b measure exactly 90°, b on b within a mi- 
nute 120°. The constancy of these characters in the appa- 
rently rhombic crystals, might alone be sufficient to disprove 
Mr Haidinger’s statements, but I may add that they equally dis- 
agree with every other crystal that I have seen, and with every 
angle I have measured. One of the crystals I have observed, 
contains planes corresponding in position with £, P, and P' of 
Mr Haidinger, whose inclinations on a he gives thus 
a on e 112° 0' 
P 111 42 
P' 111 18 
My crystal measures 
a on e 111 0 28' 
P 111 30 
P' 111 28 
[ have also measurements of planes corresponding to his 
to on P 107° 4 9 ' 
P' 107 30 
results which are wholly inconsistent with Mr Haidinger’s no- 
tion of its form. 
It is some satisfaction to me to know, that both Mr Levy and 
Mr Phillips consider Mr Haidinger’s figures incompatible with 
the specimens they have respectively examined. I have stated, 
that it is difficult to detect with certainty the source of Mr Haid- 
inger’s misconception, without seeing his crystals, but there are 
