1 18 Prof. Chapman's Mineralogical Notes. 



Fig. 6. 



[Fig. 6.] 



A = the value c found by the 

 last equation; a = l. p is re- 

 quired. 



p = cot A. 



II. 



[Fig. 4.] 



A = 60°; B= 5^?; C = 90°. 



A and B are given to find c, the angle between a polar edge 

 and the principal axis. 



. . . cosc=cot AcotB. 



(See fig. 4.) 



[Fig. 7.] 



B=?li^; C=90 o (60° + 30°); 



a=the angle between the prin- 

 cipal axis and a polar edge, as 

 found by the preceding operation. 

 Here Band a are given to find b. 



Fig. 7. 



tan 6 = 



sin a 

 cotB' 



[Fig. 6.] 

 A = the value b, found in the last operation; «=1. p is 

 required. jt^cotA. 



(See fig. 6.) 



3. Absorption of Water by Chalk. — The following results 

 (reduced to one uniform term of comparison) of a series of expe- 

 riments on the absorbent power of chalk, were performed for the 

 London (Watford) Spring Water Company in the early part of 

 last year. They confirm in all essential respects the prior inves- 

 tigations of Professor Ansted. 



(1.) Chalk from Watford, Herts: spec. grav. =2*503. Water 

 absorbed by 100 parts =18-76. 



(2.) Chalk from Ware: spec. grav. =2*511. Water absorbed 

 by 100 parts =18*68. 



(3.) Chalk from the hills above Worthing : spec. grav. 2*506. 

 Water absorbed by 100 parts =17*91. 



