£ef$re I enter ufonnew matter^ I [1)411 hegthe Readers leave 
to caftan Eye hack, as formerly^ and review what tve have 
endeavoHrd t@ do hitherto ^ that Imaf remark the concernments ^ 
whf^ and ufm what occafton I adopted the Arguments aU along 5 
ana that I may thencetakefrejh encouragement ^ and clearer inftru- 
Bion for our future Collet ions ^ 
In the laB Preface before our fourth Velum , I gave a Synop- 
fis efthemitn importance of our th:te foregoing Books ^ inferting 
4 particular tumnmendation of the extensive UfefuUefs of [one 
Artificial Inftruments lately invented. To the Catalogue of Jnflru- 
ments there recited , or hinted^ m have fince added ( in the 4;^ 
Vol.) feme Inventions or Applications i which either have not been 
formerly thought of ^ or have been long fought and in vain attempt 
ted^ or hav^e mad^ dif cover f% contrary to old Expectations , and 
tven\ometimes to the confdM Afertions of Acute and very In^ut- 
fitive wen, what Peripatecickn?^?«W endure to hear of weighing 
watnin waters There we have a Bemonflration y How to efti- 
matt 0e particular weight of any quantity of Liquors in Liquors ^ 
txa^fy^ and by ordinary Baknces and Weights, And this is per- 
formed by the fdme happy hand^ which before directed us, Honf to find 
and denominate the f>,articuUr Weight of any parcel of Air in Air^ 
erof any Pillar of Air of the whde Atmo-Jphere , of any fize^ in 
any f lace where we can corns ^ whether clear d , or laden with ex- 
halations ^ clouds \ fnom-^hail ^ or other Meteors , how high foever 
they afcenJ'^ and the fame flight EnginQthe Ballance ) hath in the 
fame hind deteffed an Atmofphere in the mo^ Solid Bodies, 
'Tis'a longtime ft nee the Mechanical Witts have consulted ^ flow 
toimprove Optical Glafles by the Hyperbolical Se5iton: There 
we have the Propofttion demon fir at ed , and the Engifi' direBtd for 
pra^ice, 7 he skill &f drawing in Perfpsitive/V as a pleafant Com- 
panion to the t ravaylor , and enables him to give a lively Hiftory 
0fhls travels for the information of others : iwe ma)find\ 
how taJraw in PerfpeBive an) objs^s both accurateh anddif- 
patehingly t by an Inflrim'n^s as any vulgar hxnd rnay draw a 
Circle more perfectly bya Compafs ^ than the m$(l perfeEi Penman 
can ddbyhis hand alone: And we have gotten a little (lep onto- 
wardi the advancing of M'tatiine^ Burning Concaves^of which the 
perfyrmanje is there particular ^fed^ 
' ' ^ We. 
