422 E.. Tuckerman on North American Lichens. 
At this elevation, as the deflecting force has xanieet eg a with the 
rotary velocity, it is evident the elevation of the a st be maintained 
force a ec © maintain it, we shall find this same value, sin? 06= ag 
Th reali Ayaka air resists igeretion as well as rotation, and hence the 
descent will’ Sear but gyroscope could S placed in a 
acuum, e slight treton at the point of support be entirely an- 
which it would forever ainate though the rotation of the disk would soon e 
by friction of the axle, entirely cease. 
Arr, XXXVII—Supplement to an Enumeration of North American 
Lichenes ; Part first, containing brief diagnoses of New Species ; by 
Epwarp Tuckerman, A.M. 
Tux following characters are intended to be as succinct as possible. It 
is hoped however that ek will preva sufficient to indicate accurately va 
ved 
y BRA FREMONTH, sp. NOV a thao cis pen ndulo ramosis- 
pruinosum cingente. Evernia, Tuckerm. Exs. n. 52. ; 
Hab. “Camp of Dee. 5, 6, 1854,” Fae Nev. ada), “ California, abund- 
ant on Pines,” Col. Fremont, (com. Torrey!) “ Hangs from the lower 
aa of all aie coniferong. trees of N sonia Galforntt, ei Sout or 
v it only about lat. 42° to 44°. etim ees 5 
te Pas as a [teat for the manufacture of their wit saisntles 
* Tf the solid of revolution is of dimensions so small that it may be oxen 
concen in its centre of gravity, it would require, in the fall of its axis 
angle 90°-§, the velocity ./2 77. cos §; and this velocity, deflected into horizontal on 
ration in a circle whose radius is 7sin 3, would ereate a centrifugal force 29 Gnd 
29 . i 
whose component normal to the axis of figure is 2 9 — es Equating to this 
opposing component of gravity gsin $, we get sin?¢ ae. as in the text. wh it 
ut this result i is only true arte the bady le no sensible dimensions, bye sts 
80 when, as in the ordinary forms of the gyroscope, the ee 0 
Cis small compared w ith A. The above value of pag is & marin jower poe 
ing , and the Smait at which the helix becom izontal becomes A-C) 
lower as Cis greater compared with .A, the general expression being sot o= ep 20 
__That this result is not given by the analysis in wna text is Ped the — wv 
Pegg strietly true; for I bebe cited he which retard the recat 
and introduced their effects on valocity, ‘n, only. 
eae 
Sa ee ee 
bal 
