Variation of the Altitude of the M^rrmW Cylinder, whick at 
moft is hardly three IncheSj may be made as diftinguilliable , as 
if it were three Foot, or three Yards, or as much more , as is 
defircd. 
The manner hereof is vifible enough by Figure I: where A 
B C reprefents the Tube, which may be either Blunt, or with 
a Head, as A B C (by which latter lliape, more room is allow'd 
for any remainder of Air, to expand the better. ) This is to be 
illed with Quickfilverjand inverted as commonly; but into a 
Veffel of Stagnant Mercury,made after the fafliion of 1 K, that 
is^ having its fides about 5 or 4 inches high, and the Cavity of it 
equally big both above and below 5 and if itcanbe( befides 
that partj which is fill'd by the end of the MercnrinU Tube^that 
ftands in it ) of equal capacity with the hollow of the Cane about 
B.* For then the Quickfilver rifing as much in the hollow of 1^ 
as it defcends at B^the difference of the height in the Receiver I,, 
will be jufthalf the ufual difference. And if the receiving VeiTeli 
IK have a bigger Cavity, the difference will be lefs^but if iefsjthe 
difference will be greater ; But, whether the difference be here- 
by made b'gger or lefs, 'tis no great matter, fince by the con- 
trivance of the Wheel and Index ( which is more fully defcribed 
in the Preface to the Micrography ) the leaft variation may be 
made as fenffhle as is defited, by diminilhing the bignefs of the 
Cylinder Ej and lengthening the FG, according to the^ 
Proportion requifite. 
An Account 
Of Four Suns, ti^hkh very lately appear dm France^ mii 
of two Raine-bows, nmfually pofited^ feen inthefam 
Kingdom^ fomewhat longer agoe. 
Thefe Phtemmena are thought worthy to be inferted here,for 
the Specuiation of the Curious io thole Kingdoms 5 as they wei>e 
pubhflit in the French JournMl dej Scavms, oih lay 10,1666. W^, 
The 9^^ ofJpril oi this prefeat yearj about half an hour paft 
nine, there appeared three C'rcles in the sky. One of them was^ 
V^ry great, a iitde interrupled^ and white every where, without 
