S88 Count de Bournon on Bardiglione, 



but not squares. From this table we perceive, that the angle of 129' 

 56', arising from the retrogradation by a single row, belongs to the inci- 

 dence of the plane produced on the narrowest sides of the prism ; while 

 that of 128° 31', which is next to it in the preceding table, belongs, on 

 the contrary, to that of the incidence on the broadest side. We also 

 see that the plane of substitution that makes an angle of 1 35° with the 

 two adjacent sides of the prism, and which would be the product of a 

 retrogradation by a single row, on the supposition of the bases being a 

 square, may likewise exist, or at least with a very trifling difference, on 

 the supposition of the Abbe Haliy. The fracture alone, and particu- 

 larly that which the crystals themselves exhibit (for I could never 

 obtain one sufficiently regular by cleavage), as well as its striking 

 parallelism with the interior indications of natural joints, and the angle 

 of 135° constantly formed by these fractures, appear to me most in 

 favour of my opinion. 



I ought however to add, that the peculiarity exhibited by the 

 crystals of this substance, of undergoing a retrogradation only on one 

 side of the edges of the primitive prism, would seem to support the 

 view taken of it by the Abbe Haliy ; though much less so than if a 

 retrogradation took place on each side, and the retrogradations were 

 of a different kind. On the whole, I think there is a majority of cir- 

 cumstances in favour of the opinion which I have formed, but on this 

 point the crystallographical reader will decide. 



