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 
contraty motions, can move with that exadlnefs and fteddinefs, 
that is required, cfpecially, for any confiderable length of time. 
Having premifed this^he difcourfes upon Mr. Hoek his Turne^ 
intimating firft of all, that he was impatient to know what kind 
of Turtle this was, imaginingjthat it had been tried, and had fuc- 
ceededj as coming from a Society that profefFeth^ they pub- 
hill nothing but what hath been maturely examin'd. But that he 
was much Turprifed when he faw the Micrography of Mr. HooJ^y 
and found there^ that his Engine was publiflied upon a meir 
Theory^ without having made any Experiment, though that 
might have been made with little charge and great fpeed ; ex- 
pence of Money and Time being the onely thing, that can ex- 
cufe thofe who in matter oiEtK^inesxm^VLX^ their inventions to 
the publickjWithout having tried themjto excite others to make 
trial thereof. 
Whereupon he propofes fome difficulties, to give the Invsn^ 
ior occafion to find a way to remove them. He affirms there- 
'fore, that though it be true in the Theory^ that ^ Circle, whofe^ 
flain is inclined to the^.w of the Sphere by an An^le\ whereof 
half the Diameter is the Sine, and which touches the Sphere in 
its TqU^ will touch in all its parts a fpkerical Surface, that fliall 
turn upoTi that Axe. But that it is true alfo, that that muft be 
h\M ^ Mathematical Circle^ and w'lthowi Breadth, and which pre- 
cifely touches the Body in its middle : Whereas in the pradl/ce, 
a Circle capable to keep Sand and Putty,muft be of fome breadth-^. 
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 
the Brim of a7(2>i?gthat is half an Inch broad. He adds, that it is 
very difficult to contrive, that the middle of the dafs do al- 
ways precifely anfwer to the Brim of \k{\% iiing, feeing that the 
pofition of the Glafs does always change a little in refped: of the 
King^ in proportion as 'tis worn, and as it muft be prefer be- 
caule of its inclination. He believes it alfo very hard, to give 
to the Axis or to the Mandril^ vi'hich holds rhe Glafs^ that little 
hiclination^. 
