Volume 1

Rohault's System of natural philosophy / illustrated with Dr. Samuel Clarke's notes taken mostly out of Sir Isaac Newton's philosophy. With additions [by R. Laughton and C. Morgan]. Done into English by John Clarke.

  • Jacques Rohault
Date:
1723
Catalogue details

Licence: Public Domain Mark

Credit: Rohault's System of natural philosophy / illustrated with Dr. Samuel Clarke's notes taken mostly out of Sir Isaac Newton's philosophy. With additions [by R. Laughton and C. Morgan]. Done into English by John Clarke. Source: Wellcome Collection.

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    ver with which it is filled, and that in which it is im- merfed, have flood tome time in a Place void of grofs Air: For in inquiring into the Reafon of this Phaenomenon, we can find no other but this, that the Quickfilver thus prepared, is cleared of tome Matter of the Phenomenon ; but upon what Caufes fo fur prizing a Thing dependsj is not fo well agreed. The Lord Bronnker thought, that the Weight of the Air was much greater than anfwers to the Height of about 29 Inches of Quickfilver, but that the Quickfilver was deprejfed to that Height, by the Air which was in- ■vifibly mixed with it (ttnlefs it was cleared of it) And after it was cleared of it, and there remained no¬ thing to refifi the Weight of the ex¬ ternal wAir, but only the bare weight of the Quickfilver then it was_ found to be otherwife ; and the Quickfilver was fupported to a greater Height, hy the Ballance of the Air. This is indeed very ingenious 5 but that which weakens very much this Explication, is, that upon theleaft fhaking of the Tube, the Quickfilver immediately ruffles down: which could by no means be, if it were fupported by an equal Weight of Air or ALther. VV herefore the famous Dr. V Vallis attempted the Thing another way. He imagined, that all real Gravita¬ tion, proceeded from the Prejfure or Spring of the Air or Wither, without which thofe inactive 'Bodies which we call heavy, if once at refi, would remain fo, without any real gravita¬ tion, or without defending, having no more Tendency to move downwards than ftdeways. The Qluickfilver therefore, when it is cleared of all Air from within, and fufpended in the aforefaid manner, when it is at ref, will con¬ tinue fo, and retain its Poftion, be¬ yond the common Height neceffary to an aequilibrium, bccaufe it is free from all Prejfure of the Air, and is notpreffed upon, either by its Gra¬ vity, or by its Spring : But if it be put in Motion, either by any fhaking of the Tube, or by any Motion within, from the Spring of the Air which was at firfl left in it, or is fnee got in, then it will continue ih it Motion down¬ wards (that way being open,) But finceitis now allowed, that Gravity does not depend upon the Air or iErhejr, but is an original con nate and immutable Affe&ion of alf Matter, neither can this Explication be admitted . And indeed this very learned Perfon confeffes, that he him- felf was not fatisfied with it. There¬ fore he adds. That the Superficies of the Tube however well polifhed, can¬ not be thought to be fo free from all Ruggednefs or Inequality, but that there mufi remain fame Roughnefs, which mufi caufe Cohxfion, or (if it be moveat) fame Trillion of the ad¬ jacent Body, whereby the Motion mufi be fomething kindred. And indeed this Opinion comes- nearer the Truth; and that chiefly becaufe upon the leaft fhaking of the Tube, the Quickfilver falls down,, whence it is manifeft, that the Suf- penfion does not depend upon any permanent Caufe, fuch as the Gra¬ vity of the Air or Aither, but upon fome accidental Thing, fuch as fome kind of Adhasfion. However, be¬ caufe there does not appear to be any fuch Roughnefs in the Superficies of the Glafs, as this learned Perfon ima- ines ; it feems to be moil: proba¬ le, that the Quickfilver remains thus fufpended from the Contall or Agree¬ ment of the Parts, the Force of which is always greateft in every Effect of Nature. Thus, a plain and fmooth Loadftone applied to a Ball of Iron fufpended on a firing from a NaiL will draw it much further from the Perpendicular, than in proportion to the Magnetick Force, if it be pulled back with a gentle and even Hand, and be not feparated by any acci¬ dental Shake. So alfo Water will afeend in a Vacuum, in finail Glafs Tubes open at both Ends. And two fmooth polifhed Marbles will not be feparated, though the grofler Air - be removed. And fo the Parts of ali i hard Bodies (and in fome meafure alfo of Liquids) cohare together by Contall, that is, by that Attr adion which always arifes from Contadf. See what is faid below at Chap. 22. Artie. 9. . All the Author’s Pains therefore a- bout fubtil Matter, and about the ] Pores-