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communihm &nnis above thirty thoufand pieces of Eight were wafred 
by theexpenceof Qiiickfilver : Which inconvenience hath pro- 
ceeded, in his opinion, from want of care in feeing the Ve{rels,ured 
in the recovering of Quickfilver, made of good fluff, and lliuc ve- 
ry clofe. Where he takes notice, that at Or^^f?, famous for Gold- 
and Silver-mines, on the top of a hill there is a little vein of white 
Earthj whereof they make Veffels for ufe, which when baked be- 
come fo clofe and firm that they are not inferior ro the htQ,Chim^ 
and are very ufeful for the making of Crucibles. But where fuch 
Earth is wanting, he direds , that that Clay, which is ordinarily 
ufed in making the veffels for recovering the Mercury , be the bet- 
ter mingled with the fcum or drofs of Iron ground very fine, and fo 
made up and baked very well ; and chat then there fliall not be fo 
much Quickfilver loft in the ufe of them,as is by thofe now in conw 
monufe,cfr. 
IIL Jnimadverfions on the Firjl fart of the ^IJCEINA CoM' 
LEStlS of the defer vedly fainous Afironofyier]o\\zm\t% Heveli" 
uSj together wth m Explication of fome INSTRU— 
^lENtS, made by Robert Hook F. of GeornAn Grefh.CoIJ. 
and Fellow of the Royal Society, London, /fr John Martyn Erin- 
ter to the R. Society, at the Bell in i'/.Pauls Church-yard, 1 674. 
THIS Piece confifts, as the Title intimates, of two main parts. 
The One reprefencs the Authors thoughts of {}\e Aftronomieal 
Organography of the Excdknt Heveli^, both examining and 
Ticho Brake's fnftruments^ and undertaking to evince, that if they 
hd^dirndtM^Qoi tele fcofical Sights, their Obfervations might have 
been much more exaft than they are ; forafmuch as,in the Author's 
opinion , an Inftrumenc of three foot radim with Ttlt^'cop^s^ 
will do more , than one of fixty foot radius with Common Sights. 
The defcribes an Inftrument for taking all forts of Angles 
and Diftances in the Heavens , which , if increased in bulk , is 
capable, faith Mr. Hook ^ of as great accuratenefs , as the Ac- 
mofphere will ever permit Cceleftial Obfervations to be 
made. Its perfefiion he places in thtft feven particulars: 
I. In the Sights y which are fuch, faith he ^ as may be made 
to difcover the minuteft part difcovcrable in an Objeft, not at all 
ftraining the eye,and fit for all eyes. 2. In the DiviJions,which are 
fuch, as will diftinguifli the Angle as minutely as the Sights wil di- 
ftinguilh the parts or objeas,and that even ro Seconds, 3. In fiich a 
contrivance of the Sights, that with one glance of the eye, both the 
Ob)eas, though a Semi'Circlediftant, arc 4;/ t^^wdiftinguifli't and 
feen . 
