Page:Reflections upon ancient and modern learning (IA b3032449x).pdf/219

 Diminution of the Weight of the Air, as of Heat and Cold. That Defect was remedied by Mr. Boyle (b), who sealed up the Liquors in the Tubes, Hermetically, that so nothing but only Heat and Cold might have any Operation upon them. The Uses to which they have been applied, may be seen at large in Mr. Boyle's History of Cold, and the Experiments of the Academy del Cimento.

2. The Baroscope, or Torricellian Experiment; so called from its Inventor, Evangelista Torricelli, a Florentine Mathematician; who, about the Year 1643. found that Quick-Silver would stand erect in a Tube, above 28 Inches from the Surface of other Quick-Silver into which the Tube was immersed, if it was before well purged of Air. This noble Experiment soon convinced the World, that the Air is an actually heavy Body, and gravitates upon every Thing here below. This Gravitation being found unequal at several Times, Mr. Boyle applied this Instrument to Mechanical Uses (c), and shewed how it might teach us to know the Differences and Changes of Weather; when dry, and when wet; since, by a vast Number of Observations, he had learnt, that in dry Weather the Air drove up the Mercury, and in wet