Royal Society. 69 
The motion of the earth is not from the perpendicular, but 
horizontal, as appears by the cracks in the earth, which are now 
to be found all o\xi Sicily j it is a vibration fo quick, that it 
cracks the glafs in the windows, and the reciprocations of a lute- 
firing are not more frequent than it j now when the vibrations 
are lo quick, and the body moved ^ large, the motion muft be 
prodigiouily violent. 
2o find the "Parallax of the fixed Stars 5 by T>r. Wallis. Phil. 
Tranf. N° 201. p. 844. 
GAlileo hath fuggefted feveral things confiderable, in order to 
the obferving of the parallax of the fixt ftars 5 as that the 
times of obfervations flioula be, when the fun or earth are in the 
^ropics^ or as near to them as poflible^ becaule at thofe times, 
if at any, will be the greatell difecnce of their meridional alti- 
tude: That the flars to be obferved, fhould be fuch as are as 
near as poffible to the pole of the ecliptic 5 for fuch as are in its 
plane, or near it, tho' they may be lometimes nearer, and fome- 
times farther from us, which might fomewhat alter their apparent 
magnitude, if it were fo much as oblervable, yet it would alter 
little or nothing the parallaftic angle : Galileo alfo oblerves, that 
in a bufinefs ^o nice, the ordinary inftruments of obfer-vation, tho* 
pretty large, would be infufficient for this purpofe • and he pro- 
poles, that by the fide of fbme edifice or mountain, at the dif 
tance of Ibme miles, the fetting of fome noted Star^-d^ that of 
Lucida Lyra might be obferved at thofe different times of the 
year, which might be equivalent to an indrument, whole radius 
were fo large; which would be a good expedient if praflicable 5 
but DrJVallis doubts the denfity of our atmofphere is fo great, as 
that it would be hard to difcern a flar juft at the horizon, or even 
within fome few degrees of it ; and that the refraction would 
there be lo great, and lb uncertain, as not to anfwer lo curious an 
obfervation: What occurred to the Doctor upon thele confidera- 
tions, was to this purpofe; that fbme circumpolar ilars, nearer 
to the pole of the Equator than is our Zenith, and not far from 
the pole of the Zodiac, fhould be made choice of for this pur- 
pofe; and in cafe the meridional akjtude be dilcernibly dififerent 
at different times, fo will alfb be their utmofl eaft and weft azi- 
muth, which may be better obferved than their rifing and let- 
ting; and this will not be obnoxious to the refraction, as the me- 
ridional altitude is; for tho' the refraction do affedt the altitude, 
yet not the azimuth at all ; and we may here have choice of ftars 
for the purpofe, which in obfervations from the bottom of a well, 
we 
