Curious and nice d i ft i n gu i fhi n g of which fmall changes , Mr. 
in the Preface to his Micrography , has defcribed fuch an 
Inftrumeut with a Wheels contrived by himfclF, and , by thefe 
two laft years trials of it, coufhntiy found mod exadt for that 
purpofc ; which being fo accurate, and not difficult to be 
made, it were defirable, that thofe who have a Genius and op- 
portunities of making Obfervations of this kind, would fur- 
mih themfclves with Inch of thefe Inftrnments, as were exactly 
made and adjufled accordingto the Method, delivered in the 
newly mentioned place. 
To fay fomethingof the Obfervations, made by this In- 
ftrument, and withal to excite ftudious Naturalijh to a {edit- 
ions profccution of the fame, the Reader may firfi take notice, 
that the lately named Mr. Boyle hath (as himfelf not long fince 
did intimate to the Author of thefe Trails ) already made di- 
vers Obfervations of this kind in the year 1659. and 1660. 
before any others were publick , or by him fo much as heard 
of $ though he has hitherto forborn to divulge them, becaufe 
of fom.e other Papers (in whole Company they were to ap- 
peat) which being hind red by other ftudies and employments, 
he hath not as yet fiiiifhed. 
Next , that, beiides feveral others, who, fince have had the 
curiofity of making fuch obfervations,the Worthy and Inqui- 
fitive Dr. John Beal, is doing his part with much affiduity (of 
which he hath by feveral Letters acquainted his Friends in 
London) both by obferving himfelf , and by procuring many 
Correfpondents in feveral places in England 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 difeovered, whether the Aire gravitates more 
in the parts of the Earth lying more E aft or Weft , North or 
S outk > whether on fuch as lie neerer to the Sea , or further up 
into the Main land ? in hotter or colder weather ■? whether in 
high 
