carious and nice diftinguiftiing of which fmall changes y Mr. 
Ji»6l^ in the Preface to his Micrografhy ^ has.dcfcribed fiich an 
Inftruinent with a Wheels contrived by himfelf, and 5 by thefe 
two laft years trials of it, conftantly found moft exaiS: for that 
purpofcr which being fo accurate 5 and not djfficult to be 
made, it were defirable^ that thofe who have a Genius and op- 
portunities of making Obfervations of this kind, would fur- 
iiifli themfelves withluch of thefelnftrnments^as were exactly 
made and adjufted according to the Method, delivered in the 
newly mentioned place. 
To fay fomcthingof the Obfervations^ made by this In- 
ftrument, and withal to excite ftudioas JV^^e^r^///?/ to a fedu- 
lous profecution of the fame, the 'Reader may ^rjl take notice, 
that the lately named Mr. Boyle hath (as himfelf not long fince 
did intimate to the Author of thefe Tr^iS/ ) already made di- 
vers Obfervations of this kind in the year 1^5-9. and 1^60. 
before any others were publick , or by him fo much as heard 
of 5 though he has hitherto forborn to divulge them, becaufe 
of fomc other tapers ( in whofe Company they were to ap- 
pear) which being hindred by other ftudies and employments, 
he hath not as yet finilhed. 
Hext , that, befides fcveral othersj who, fince have had the 
curiofity of making fuch obfervationSjthc Worthy and Inqui- 
fitive Dr.7(?iw 5^/, is doing his part with much affiduity (of 
which he hath by feveral Letters acquainted his Friends in 
ion^flw) both by obferring himfelf ^ and by procuring many 
Correfpondents in feveral places in for the fame pur- 
pofe ; judging it of great importance , that Obfervations of 
this kind be made in parts fomewhat diftant from one another, 
that fo from many of thofe , accurately made and then com- 
pared, it may be difcoveredj whether the Aire gravitates more 
in the parts of the Earth lying more Eajl or fFeJi, U$rth or 
South ? whether on fuch as lie neerer to the Sea^ or further up 
into the Main land f in hotter or colder weather ? whether in 
high 
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