of the Mtrosoterpenes of Dr. Tilden. 



131 



Calcula- 

 tion. 



II. 



Ame- 

 rican. 



III. 



French. 



IV. 



Juniper. 



V. 



Calculation. 



ram, 

 mb 

 mm' 

 .mm' 



-ac 



ah 



ad 



i-ca' 



f-mc 

 cm' 

 mp 

 pc 

 .my 



-md 



m'8 



du 



m'p 



m' u 



mu' 



p' 771 

 m'\ 



rbp 

 \jp' 



rtnJc 

 mu 

 um' 

 m't 

 f m 

 hm' 



uu' 

 tt' 



m(c)m' 



ap 



53 4 



36 56 



73 52 



106 8 



70 W 

 43 m 



78 18 



101 42 



37 26 



40 52 



86 20 



57 43 

 64 34 



23 24 



52 20 



O / 



53 4 

 36 56 

 73 52 



70 19 



109 40 



57 41 

 64 35 



23 25 



52 28 



74 19 

 105 55 



75° to 75° 19' 

 105 18 



78 18 



101 42 



37 25 



40 38 



30 8 



58 35 



120 45 



17 4 



86° to 87° 15' 



78° W | 21 



10f 47^ 



37 55^ 



40 45 



29 31 



58 27 



87 9 



75° T to, 

 approx. 



93° approx. 



46°30'to48°8 

 131 approx. 

 92 30 

 87 17 



75 



53 55 



19°4b V to20°28' 



about 63° 35' 



64 30 

 46° 55' I 47° 32' 



about 28° 



91 40 



87 22 

 67° 30' to 70° 



28° 40' approx. 



52 50- 



37 10 



74 20 



105 40. 



70 23-i 

 43 38 I 

 29 52 



78 181 

 101 42 

 37 22 

 40 56 

 30 3 



58 25 1 

 121 35 



16 39 



86 51^ 

 104 56^ 



75 4 



54 2| 

 93 8| 

 20 3^ 



64 26 



64 4 " 

 47 12 



132 48 

 92 40£ 



87 19} 

 68 32f_ 



29 48 

 40 59 



A facile cleavage runs parallel to the face (0 01); a less 

 facile cleavage is parallel to the faces of the form {110}. 

 The great facility with which the former cleavage is produced 

 precluded the forming sections for the polariscope. 



In one crystal which showed one of the ring-systems the 

 plane of the optic axes was evidently perpendicular to the 

 plane of symmetry, the acute "bisector lying in that plane ; and 

 it appeared that the dispersion of the bisectors in that plane 

 for different colours gave the position of the bisector for blue 

 rays nearer to the normal of a, or (1 0) ? than that of the red 



