TEOGKESS OF PHYSICS. 179 



could not be disentangled. In hydrostatics, Steviuus had 

 extended and applied the discovery of Archimedes. Tor 

 ricelli had proved atmospheric pressure, &quot; by showing that 

 this pressure sustained different liquids at heights inversely 

 proportional to their densities ; &quot; and Pascal &quot; established 

 the necessary diminution of this pressure at increasing 

 heights in the atmosphere : &quot; discoveries which in part 

 reduced this branch of science to a quantitative form. 

 Something had been done by Daniel Bernouilli towards 

 the dynamics of fluids. The thermometer had been invent 

 ed ; and a number of small generalizations reached by it. 

 Iluyghens and Newton had made considerable progress in 

 optics ; Newton had approximately calculated the rate of 

 transmission of sound ; and the continental mathematicians 

 had succeeded in determining some of the laws of sonorous 

 vibrations. Magnetism and electricity had been consid 

 erably advanced by Gilbert. Chemistry had got as far as 

 the mutual neutralization of acids and alkalies. And 

 Leonardo da Vinci had advanced in geology to the con 

 ception of the deposition of marine strata as the origin 

 of fossils. Our present purpose does not require that 

 we should give particulars. All that it here concerns us 

 to do is to illustrate the consensus subsisting in this stage 

 of growth, and afterwards. Let as look at a few cases. 



The theoretic law of the velocity of sound enunciated 

 by Newton on purely mechanical considerations, was found 

 wrong by one-sixth. The error remained unaccounted for 

 until the time of Laplace, who, suspecting that the heat 

 disengaged by the compression of the undulating strata of 

 the air, gave additional elasticity, and so produced the 

 difference, made the needful calculations and found he was 

 right. Thus acoustics was arrested until thermology over 

 took and aided it. When Boyle and Marriot had discov 

 ered the relation between the density of gases and the 

 pressures they are subject to ; and when it thus became 



