Weather let it fall again; though never lower than 28 Inches, and scarce ever higher than 32.
3. These Observations, with other Collateral Experiments, induced him to believe that the Air was, in Truth, a Springy Body, which expanded or contracted it self in a Reciprocal Proportion, to the Increase or Lessening of the Compression of the Ambient Bodies. For which he invented an Instrument to draw the Air out of Vessels that were filled with it, by Suction. The first Essays of that kind seem to have been made some Years before his appeared, by Otto Guerick of Magdebourg; but as he applied them chiefly to the Gravitation of the Air, without taking any notice of its Spring; so they were very imperfect, when compared to Mr. Boyle's. By this Air-Pump, as it is usually called, he discovered Abundance of Properties in the Air, before never suspected to be in it. What they are, either considered singly, or in their Operations upon all sorts of Bodies, may be seen at large in his Physico-Mechanical Experiments concerning the Weight and Spring of the Air; and in several of his other Discourses upon the same Argument; some of which are printed by themselves, and others in thePhi-
