( 240 ) 
My — a? D,?m)3 —+ aM °m, J al,’ 1 eee GeO ea Hae De Tete Se Ns 
. . . . Ld hd e e . . . 
ae Ton bj act 
or ME zes een 
This form is the same as that obtained in equations with one 
measured quantify"), so that here also the weight of the result is 
found from the coefficients, which occur in the solution for ., U, Een 
if the quantities |yX./,| ete. in the normal equations are left unde- 
termined. 
Mineralogy. — “On the behaviour of disthene and of sillimanite at 
high temperature.” By E. H. M. Berkman. (Communicated by 
Prof. SCHROEDER VAN DER Kork). 
In nature occur three varieties of aluminium-silicate (Al, Si O,) 
Le. disthene, andalusite and sillimanite. Sillimanite and andalusite 
are orthorombic; disthene however triclinic. So the two first show 
parallel, the last oblique extinction. 
According to the experiments made by VurNapsky*), disthene is 
said to turn into sillimanite, at about 1350 degrees; the same tem- 
perature is said to turn also andalusite into sillimanite. As a proof 
that they had actually become sillimanite, he urged that, whereas 
before being heated, their hardness and specific gravity differed, 
they now showed the same. Moreover the extinction of disthene 
had become parallel. 
The results to which he came are these: 
RE eenen 
| S.G. before S.G. 
Name. | heating. (after heating. 
Frets : 3.045 : 
Sillimanite | 3 986 id. 
| pe 
5. Se BEAD 
Disthene 3 AB | 3 90 
| 
Andalusite DES 3.165 
Directed by Prof. SCHROEDER van DER Kork, I experimented, as 
stated by VRRNADSKY, and came to the following results, as to their 
specifie gravity: 
1) See for instance Merriman, Method of least Squares, p. p. 83 and 84. 
*) See Bulletin de la Société Min. de France (1889 et 1890), 
