A plan of a course of lectures on the principles of natural philosophy / By the Rev. S. Vince.

  • Vince, Samuel, 1749-1821.
Date:
1793
Catalogue details

Licence: Public Domain Mark

Credit: A plan of a course of lectures on the principles of natural philosophy / By the Rev. S. Vince. Source: Wellcome Collection.

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    of the rarity r, we have 7 : log. 4 :: *: log. r, and hence rn 4]^; alfti x ~ 7 X —^— =3 1,1626 x log.miles. This rule fuppofes the den- og- 4 hty to be as the compreflive force, which is not true unlefs the tem- perature remains the lame; but as the temperature is found to be very different at the lame time at different altitudes, the rule will require a correction according to the altitudes of the thermometers at the two places. Omitting however this correction, the denfity of the air at the altitude of 45 miles is found to be 7420 times lefs than at the earth’9 lurface; and yet, from obfervations on the twilight, the rays of light are fenlibly affeCted by the air at that altitude. ON THE BAROMETER. 53. If a glafs globe be exhaufted of air and balanced at one end of a beam, upon admitting the air the globe preponderates. This experiment clearly proves that the air has Weight; and from' the weight neceffary to balance the globe after the admiffion, the weight of the air will be known. Mr. Cotes found the deniity between 800 and 900, but nearer to 900, times lefs than water; and Mr.Ha uksbee made it 8S5 times lefs, when the barometer Hood at 29 j- inches. Hence, as a cubic inch of water weighs 253,18 grains troy, a cubic inch of air weighs 0,286 grains. If we take mercury to be 14 times heavier than water, the fpecific gravity of air : that of mercury :: 1 : 8S5 r X 14= 12590. 54. If a glafs tube more than 3 1 inches long, hemeticaliy fealed at one end, be filled with mer- cury and then inverted and its end immerfed in a bafon of the fame fluid, it will Hand at an alti- tude above the furface of the mercury in the ba- fon between 28 and 3 1 inches. As the mercury defeends from the top of fhc tube it mull leave a vacuum, and it remains fufpended by the preffure of the air upon the furface of the mercury in the bafon, for if the air be taken off from the furface the mercury defeends. This preffure of the air was difeovered by Ci.uii.ko. He found by experiment that water might be railed by the common pump to a certain height, and no higher; whereas-, had nature abhorred a vacuum, as the philoiophers then thought, it might have been railed to any height. He conjeftured therefore that! it was owing to the air’s gratitation. Afterwards his pupil Torri- celli u s