Lectures on select subjects in mechanics, hydrostatics, hydraulics, pneumatics, and optics, with the use of the globes, the art of dialing, and the calculation of the mean times of new and full moons and eclipses / [James Ferguson].

  • Ferguson, James, 1710-1776.
Date:
1790
Catalogue details

Licence: Public Domain Mark

Credit: Lectures on select subjects in mechanics, hydrostatics, hydraulics, pneumatics, and optics, with the use of the globes, the art of dialing, and the calculation of the mean times of new and full moons and eclipses / [James Ferguson]. Source: Wellcome Collection.

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    each other fo ftrongly, as to require a force much greater than their own weight to feparate them. And this cannot be owing to the preffure of the air, for the fame thing will hold in an ex- haufted. receiver. 5. If two polifhed plates of marble or brafs be put together, with a little oil between them to fill up the pores in their furfaces, and prevent the lodgement of any air; they will cohere fo Strongly, even if fufpended in an exhaufted re- ceiver, that the weight of the lower plate will not be able to feparate it from the upper one. In putting thefe plates together, the one fhould be rubbed upon the other, as a joiner does two pieces of wood when he glues them. 6. If two pieces of cork, equal in weight, be put near each other in a bafon of water, they will move equally fait toward each other with an ac- celerated motion, until they meet: and then, if either of them be moved, it will draw the other after it. If two corks of unequal weights be placed near each other, they will approach with accelerated velocities inverfely proportionate to their weights: that is, the lighter cork will move as much fafter than the heavier, as the heavier exceeds the lighter in weight. ‘This fhews that the attraction of each cork is in direct propor- tion to its weight or quantity of matter. _ This kind of attraction reaches but to a very {mall diftance; for, if two drops of quickfilver be rolled in duft, they will not run together, be- caufe the particles of duft keep them out of the fphere of each other’s attraction, epul- till they are wet; and hence it is, that a {mall B 3 needle,