MODERN SCIENCE. 193 



force on all equal surfaces, and in a direction at right angles 

 to those surfaces" This law led to the invention of the 

 HYDRAULIC PRESS by Bramah in 1796, and later, of many 

 machines of tremendous power, such as levers, jacks, lifts, 

 boring and perforating tools, which save immense time and 

 labour all being direct applications of it. Of Pascal's 

 mathematical works, his Traite de la Roulette is the most 

 famous, being a treatise on the Calculus of Probabilities. 



162995. Huygens constructed a PLANETARIUM, in 

 conformity with the Copernican system, and which led to the 

 discovery of CONTINUOUS FRACTIONS ; calculated that the 

 centripetal force at the distance of the moon would be only 

 a fraction of 15 feet per second ; ascertained the VELOCITY 

 OF A FALLING BODY in any latitude. 



1642 1727. Newton worked out his METHOD OF 

 FLUXIONS (1665), which, like the Differential Calculus (of 

 Leibnitz), is one of the most powerful instruments in mathe- 

 matics. This was his first great discovery. We shall see 

 further on that he was a stranger to no science, and turned 

 his attention, not to astronomy only, but to physics also, 

 introducing the idea of attraction even into chemistry; his 

 discoveries on the reflections, refractions, inflections, and 

 colours of light, and likewise on sound, would have sufficed 

 to make him famous. 



16461716. Leibnitz, like Newton, opened a new field 

 in mathematics, by his discovery of the DIFFERENTIAL 

 CALCULUS the basis of higher analysis which is to the 

 mathematician what the microscope is to the naturalist. 

 This Calculus and the Fluxions of Newton are about equal 

 in power, but Leibnitz's Calculus is easier to handle: it 

 almost requires a Newton to handle the formidable Fluxions 

 hence the Differential Calculus is more used. As a geo- 

 logist, Leibnitz propounded the doctrine of the GRADUAL 

 COOLING OF THE GLOBE, the subsidence of its strata by 

 fracture, the deposition of sedimentary rocks and their 

 induration. Of Leibnitz's metaphysics, so famous and 

 influential for a time, we cannot speak a word here. 



1654 1705. Bernouilli (James), one of the very pro- 

 foundest mathematicians, by calculating the return of a 



