390 ACTUAL WORKING IN ORIGINAL RESEARCH. 



in any given case ; for instance, the property of chemical 

 force, of causing dissimilar substances to unite together 

 only in definite proportions by weight, and produce a 

 third homogeneous substance of .widely different apparent 

 properties, enables us to detect that force in any new case 

 of chemical change that occurs. 



Quantitative methods have been and are almost in- 

 exhaustible sources of new scientific knowledge, and a 

 multitude of discoveries, many of which are of the 

 highest value, might be described, which have resulted 

 from the employment of processes of accurate measure- 

 ment. By means of them Galileo discovered the laws 

 which regulate the descent of falling bodies, and found 

 that, when the time of descent was doubled or tripled, the 

 space traversed became four or nine times greater, and 

 therefore that the spaces fallen through were proportional 

 to the squares of the times of descent ; and a knowledge 

 of this law, that the earth exercised the property of 

 attracting bodies, with a power which varied inversely as 

 the square of the distance, largely enabled Newton to 

 discover the universal action of gravity, by showing that 

 the law agreed with the motions of the heavenly bodies. 

 Great progress in chemical science has been due to the 

 introduction by Lavoisier of the use of the balance ; and 

 the errors in Stahl's theory of phlogiston were chiefly 

 discovered by the aid of that instrument ; the chemically 

 combining proportions of substances were found by means 

 of accurate weighing ; and the use of the goniometer in 

 measuring the angles of crystals resulted in various 

 geometrical discoveries in the science of crystallography. 



One of the grandest proofs of the value of measurements 

 was the discovery of the equivalence of all the physical 

 forces and chemical elements, and of their indestructi- 

 bility ; and another was that of the system of atomic weights 



