39S 



Rev. C. S. Lyman on the Pendulum Experiment 



figure 2, and, the large lateral planes of figure 2 are wanting in 



The angles obtained are as follows, together with those 



figure 1. 



given by Shepard and the corresponding angles of Brookite, 



Eumanite. 



Shepard. 



Eumanite. 

 Dana. 





M:M 



Brookite. 



123 



i' 



e' 



a' : a' (over base) 

 a' : a' (over summit) 



M:e' 



118°-118°30^ 



S' : e'' 

 ^ :a 

 if :a' 

 a :e' 

 a :o 



151^ 30' 

 159° 30' 



121° 40' 



121° 30' 

 144° 20' 

 128° 20' 

 156° 30' 



100°-101°(fr.e:e") 



123° 08' (fr. ^:M) 



121°-124° (observed) 



139°-142° 



102° 11' (fr. a' : a^ over summit) 102° 24', Lev 



17° 49' 



118° 26' 



108°-110° 



130°-130° 30' 130^-130' 18 



150° 12' 



159° 28' (fr. e': e' and e") 



140° 02' 



119° 30' 



141° 5 {calc. fr. o' : a') 



The first two of the angles of Brookite mentioned are angles 

 of a vertical and horizontal prism, and consequently they deter- 

 mine the dimensions of the crystal and prove the identity as per- 

 fectly as if all the other angles were added, the others being 

 deducible from these by calculation. In figure 2, the edges 

 between e, e', e'' are parallel ; those between a' and the o either 

 side of the plane a'; and those between o, e', e', o are parallel 



Figure 2 has the faces, (adopting Levy's fundamental form and 

 axes of Brookite, a = 0-5558, b{e to e) — 0"5957, c = l), 



ocPx , jPx , 2P|, ocP2, ocP3, aPf, 2P|, P|, ccPx 



e 



a 







e 



M 



e 



e 



e 



// 



Calculating from these axes gives, e':e 



149°. e' 



} 



e 



139° 53^ 



e'' : e" 



159° 20^ e':e''=12U° 41', o:o(overe') 



100° 26/ 



New Haven, Sept. 23. 



I 



Art. XLII. — Observations on the Pendulum Experiment; by 



Rev. C. S. Lyman. 



The fact that the plane of vibration of a free pendulum has a 

 movement in azimuth around the vertical, had been observed by 

 many experimenters, before it was brought so prominently into 

 notice by M. Foucault in connection with the rotation of the 

 earth- This movement is distinctly described, and illustrated by 

 a figure, in some manuscript observations on the motion of a 



