Hydrostatics.

which Book the skilful Author proposes the followingUses to be made of Hydrostatic Knowledge, viz.

2. Firsts To explore the Nature and Difference ofFossils by finding their specific Gravities. For since themost pure and homogeneous Kind of Stones are in Gra-vity to Water as about to i ; and Tin, the lightestof Metals, is to Water in Gravity as about 7 to 1 ; isastony Substance be found to have a greater Proportion ofGravity than that of 2f to 1, it must be probable that ithas in it some adventitious Matter of a metalline Nature,or is at least commixed with some mineral Body more hea-vy than pure Stone, and may therefore very probably beusefully applied to some medicinal Purposes. For In-stance of this Kind, he mentions Lapis Hæmatites orBlood-stone, Lapis Lazuli , the Load-stone, and LapisCalaminaris ; all which have their Uses in Physic.

3. Secondly , He proposes this Method as very certainto determine whether a Body, supposed to be a Stone ofthe mineral Kind, be so indeed. Thus Coral, which,fays he, some take to be a Plant, and others a Litbo-dendron, but most reckon it among precious Stones, isin Gravity to Water as 2,68 to 1, which favours thelast Opinion. Thus a Calculus humanus and a Bezoarwere found as 1,7 and 1,5 to 1, and therefore too lightto be of the fame Species with common Stone.

4. A Third Use which he proposes is to discover theResemblance or Difference between Bodies of the fameDenomination, and thereby to collect and ascertainthe several Degrees of Goodness respectively. Whencehe argues the Necessity of this Sort of Knowledge toPhysicians, Chemists, Apothecaries, Druggists ; to theGoldsmith, the Merchant, the Miner, tfc.

5. A Fourth Use is to discern genuine Stones fromcounterfeit ones, which may be of great Help to Jewel-lers. Here he gives Instances of factitious Coral andfactitious Gems, and a Bezoar, which he found outthat Way not to be genuine, though a great Price wasset on the latter.

6. Hence Mercury is found to have a different Gra-vity, being sometimes but j 3s, and sometimes above14 Times heavier than Water; and hence a notableDifference may arise in two Weather-glasses at the

X 4 fame

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