316 THE PRINCIPLES OF SCIENCE. 



construction of the thermometer, and it has recently been 

 advanced by the introduction of the thermo-electric pile. 

 Chemistry has been created chiefly by the careful use of 

 the balance, which forms a unique instance of an instru- 

 ment remaining substantially in the form in which it was 

 first applied to scientific purposes by Archimedes. The 

 balance never has been and probably never can be im- 

 proved, except in details of construction. On the other 

 hand, the torsion balance, introduced by Coulomb towards 

 the end of last century, has rapidly become essential in 

 many branches of investigation. In the hands of Caven- 

 dish and Baily, it gave a determination of the earth's 

 density ; applied in the galvanometer, it gave a delicate 

 measure of electrical forces, and was essential to the 

 introduction of the thermo-electric pile. This balance is 

 made by simply suspending any light rod by a thin wire 

 or thread attached to the middle point. And we owe to 

 it almost all the more delicate investigations in the theo- 

 ries of heat, electricity, and magnetism. 



Though we can now take note of the millionth of an 

 inch in space, and the millionth of a second in time, we 

 must not overlook the fact that in other operations of 

 science we are yet in the position of the Chaldaaans. Not 

 many years have elapsed since the magnitudes of the 

 stars, meaning the amount of light they send to the 

 observer's eye, were guessed at in the rudest manner, and 

 the astronomer adjudged a star to this or tfi&t order of 

 magnitude by a rough comparison with other stars of the 

 same order. To the late Sir John Herschel we owe an 

 attempt to introduce an uniform method of measurement 

 and expression, bearing some relation to the real photo- 

 metric magnitudes of the stars d . Previous to the re- 



d 'Outlines of Astronomy,' 4th ed. sect. 781, p. 522. 'Results of Ob- 

 servations at the Cape of Good Hope,' &c., p. 371. 



