102 G. H. Williams — Rock-cutting Machine. 



The calculated angles are those from Dauber's* measure- 

 ments from which we have the elements, 



d:b:c = 0-63446: 1 : 1 -26574 aug. (? = 89° 51' 20" 



Calc. Meas. 



c-u 001 -100 89 51* 89° 36' 



a-»i 100a 110 32 23* 32 26* 32 26* 



mrAmi 011-011 76 37 76 37 



a -n 100-111 38 55 38 52 38 53 



a-?n x 100-011 89 55 89 50 



Ca« 001-111 66 57 66 49 



a*x 100-102 45 0* 44 52 



a-« 100- 104 63 22* 63 16 



a- j 100-102 45 08f 45 12 



c-fir 001-012 32 19f 32 15 . 32 24 32 08 



c-?re x 001 aOU 51 41* 51 41* 51 35 



e- e 112- 112 48 19* 48 2l" 



a-e 100- 112 49 57 49 59 



a^o 100-120 51 45* 52 19 



a- Q 100- 122 58 12 58 10 



a- U 100- 123 62 58 62 54 



a* [3 100 a 12 1 53 43* 53 41 53 42 



c-/3 001-121 72 41 72 33 



c- Q 001 - 122 57 58* 57 59 



c- U 001-123 47 0* 46 54 



Probably the largest European crystals of datolite are those 

 from Baveno, Italy. One of these described by Sellaf is 

 mentioned by Brush J as being 4/5 X 3*75 Xl'5 inches. 



Laboratory of Mineralogy and Petrography, 

 Sheffield Scientific School, Oct., 1892. 



Aet. XIII. — A New Machine for Cutting and Grinding 

 thin sections of Rocks and Minerals • by Geoege~ H. 

 Williams. 



A beief description of a new machine for cutting and 

 grinding rock sections in which electricity furnishes an eco- 

 nomical and satisfactory motive power, may prove acceptable 

 to the constantly increasing number of workers in mineralogy 

 and petrography. This machine was devised for the petro- 

 graphical laboratory of the Johns Hopkins University over a 

 year ago, and since then it has been in more or less constant 

 use. It has thoroughly established its reputation for accurate 

 and rapid work, while experience has suggested some improve- 

 ments on the original model. 



*Pogg. Ann.. 103. 116, 1858. 



f Wien. Akad Berichte, xxix, 239. 



% VIII Supp. Dana's Min. This Jouitl., May, 1860, vol. xxix, 2d series. 



