greater than can eafily be imagined. Wherefore he could never* 
having fome experience of this precifenefs, conceive, that a 
Turn-lathe^ wherein muft be two different, and in fome manner 
contrary motions, can move with that exadnefs and fteddinefs* 
that is required, especially, for any confiderable length of time. 
Having premifed this,he difcourfes upon Mr. Hook his Turne , 
intimating 6rft of ail, that he was impatient to know what kind 
of: Turne this wasjimaginingphat it had been tried, and hadfuc- 
eeeded, as coming from a Society that profefieth, they pub- 
till nothing but what hath been maturely examin'd. But that he 
was much furprifed when he faw the Micrography of Mr. Hoof, 
and found there, that his Engine was publifhed upon a meet 
Theory , without having made any Experiment, though that 
might have been made with little charge and great fpeed j ex- 
pen ce of Money and Time being the onely thing, that can ex- 
cufe thofe who in matter of Engines impart their inventions to 
the pnblick, without having tried them, to excite others to make ; 
trial thereof. 
Whereupon he propofes fome difficulties, to give the lnvcn - . 
tor occafion to find a way to remove them. He affirms there- . 
fore, that though it be true in the Theory , that a Circle, whofe i 
Plain is inclined to the Axis of the Sphere by an Angle , whereof! 
half the Diameter is the Sine , and which touches the Sphere in i 
its Pole, will touch in all its parts a fpherical Surface , that {half i 
turn upon that Axe. But that it is true alfo, that that muft be : 
but a Mathematical Circle, and without Breadth, and which pre-. 
cifely touches the Body in its middle : Whereas in the pradice, , 
a Circle capable to keep Sand and Putty, muft be of fome breadth j . 
and he knows not whether we can find fuch a dexterity of 
keeping fo much of it, and for fo long a time, as needs,' upon i 
the Brim of a J^ing that is half an Inch broad. Pie adds, that it is; 
very difficult to contrive, that the middle of the Glafs do a!- ■ 
ways precifely anfwer to the Brim of this Ring, feeing that the : 
pofition of the Glafs does always change a little in refpedef the : 
Ring) in proportion as ’tis worn, and as it muft be preffed be- . 
caiife of its inclination. He believes it alfo very hard, to give : 
to the Axis or to the Mandril, which holds the Glafs, that little i 
Inclination 
