266 A SHORT HISTORY OF SCIENCE 



Every student should read the earlier parts of Newton's Optics in 

 which are described the fundamental experiments on the decomposi- 

 tion of white light. LORD RAYLEIGH. 



The work of Christian Huygens, towards the end of the seven- 

 teenth century, second only to that of Newton, both in extent and 

 importance, touched upon a great variety of subjects, including 

 some in the natural sciences. As a young man he wrote upon 

 geometry ; in early middle life he invented the cycloidal pendu- 

 lum. He was the first to apply pendulums to clocks and spiral 

 springs to watches, and to devise the achromatic eye-piece which 

 still bears his name. He also made a telescope and, finally, at 

 the age of fifty, observed the phenomena of polarization and, 

 most important of all, proposed the modern wave theory of light. 



THE FIRST SCIENTIFIC INSTRUMENTS: TELESCOPE, BAROM- 

 ETER, THERMOMETER, AIR-PUMP, MICROSCOPE, MANOMETER. 

 The complete history of the origin of the telescope, the ther- 

 mometer and the microscope is not known. The account usually 

 given of the invention of the telescope makes it accidental and 

 due to the children of a Dutch spectacle maker, named Jansen, 

 who while at play happened to bring together two lenses in such 

 a way that a distant church spire seen through them looked mag- 

 nified and near. The father, whose attention was drawn to the 

 phenomenon, seeing in the arrangement a source of profit, there- 

 upon made and sold the combination as a toy or "wonder," under 

 which form it was on sale in 1609, becoming known to Galileo, who 

 instantly realized its importance and made improvements in it. It 

 appears that soon after 1609 Galileo had a fairly good instrument, 

 magnifying 8 diameters, with which he was quickly and easily 

 able to make some of his most splendid astronomical discoveries. 



The early history of the telescope shows that the effect of com- 

 bining two lenses was understood by scientists long before any partic- 

 ular use was made of this knowledge; and that those who are 

 accredited with introducing perspective glasses to the public hit by 

 accident upon the invention. Priority was claimed by two firms of 

 spectacle-makers in Midd^lburg, Holland, namely Zacharias, miscalled 



