existence of positive levity," the British philosopher was working in similar fields; he improved the air-pump (invented in 1650 by Otto de Guericke), devised a physico-mechanical experiments touching the spring of the air," discovered the fundamental truth known as "Boyle's Law," invented the manometer, and made a great variety of observations in chemistry and physics of prime importance. All this work qualified him for thermometrical studies, and it is said that he constructed a "sealed weather-glass" before he saw the Italian instrument, but this is improbable.
Boyle graduated the stems of thermometers with "little specks of amel" into inches and fractions as small as sixteenths; in one experiment he found that "sal-armoniac" dissolved in water "made it descend to 2-11/16 inches in a quarter of an hour. He observed that thermometer stems were not sufficiently even and cylindrical, being often widest near the bulb, and said this was a source of inaccuracy.
Boyle felt the need of a standard permitting comparison of effects shown by different thermometers, and expressed it thus: "We are greatly at a loss for a standard whereby to measure cold. The common instruments show
