NEW OBSERVATIOXS OF THE PLANET MEnCFRY. 
441 
fl^ 
lABLE HI. 
■I- 
LONGITUDE OF TESTLDO-IJPOTO, 1897. 
From the above, then, we see that the period of rotation is i.sochronous with the 
period of orbital revolution 
As 
time of 
chances that a mass detached from the primal ne1)nhi sliould 
event, are b 
bital revolution, even 
t one in infinity, we 
der the conditions mo^t fa\- 
fo such nn 
uch isochronism must he an aft 
abo 
giving off. Now the only force capable, «o far nc wn know, ot bringing 
•iction. In Mercury, then, we have before us the first planetary 
f 
instance of tidal action. 
12. 
Axis of Rotation. 
That the axis of rotation h practio.Uy ror^onXcuhv 
is shown by the fact that the movc.nent of the mnrkm- 
to the plane of the orbit . 
due to libration is perpendicular to the terminator. No deviation from pe 
larity was at any time apparent. 
I'jien* 
hcu- 
.1 
