DISCOVERY BY MEANS OF NEW INSTRUMENTS. 475 



the velocity of sound. Cagniard de la Tour, by means 

 of his syren, discovered the number of pulsations of air 

 in a second which corresponded to each pitch of sound ; 

 and it was by the aid of glass rulers and plates, and 

 paper rings upon rods, that Chladni, and also Savart, 

 studied the vibrations of bodies, and found various new 

 truths. It was chiefly by means of the balance (which 

 had not till then been extensively used in chemistry) 

 that Lavoisier, about the year 1778, tested the theory 

 of phlogiston, and discovered its falsity ; he also dis- 

 covered that oxygen was a constituent of water, of acids, 

 and of rusted metals ; and was largely enabled to prove 

 and discover the modern theory of oxidation, combus- 

 tion, and general chemical union. By the aid of that 

 instrument, Wenzel and Eichter also were led to dis- 

 cover the doctrine of definite proportions in chemistry. 

 Cavendish, partly by the aid of his pneumatic trough, 

 which he had invented in the year 1765, was enabled, 

 in the year 1779, to discover the identity of 'fixed air' 

 (i.e. carbonic acid) from various sources; the peculiar 

 properties of ' inflammable air ' (i.e. hydrogen), its great 

 lightness, and suitability for filling balloons. Early in 

 1 840, Wheatstone invented an electric chronoscope ; and 

 Brequet and Konstantinoff, in 1843, improved it. In 

 1844, Pouillet invented another. Noble and others, in 

 recent times, by the aid of similar instruments, have 

 determined the velocity of a shot whilst being fired 

 through the bore of a gun. 



By means of his telescope, Galileo discovered the 

 secondary light (i.e. that received from the earth) of the 

 moon ; also the four moons of Jupiter ; the phases of 

 Venus ; the spots on the sun, their periods, &c. . 6 It is 

 well known that Galileo constructed his telescope about 

 the year 1609, and proceeded immediately to apply it to 



