148 Britain's Heritage of Science 



In Optics he invented the stereoscope and conducted valuable 

 experiments on the physiology of vision. At the British 

 Association in 1871 he exhibited an instrument by means 

 of which the solar time could be determined by utilizing 

 the polarization of the blue light of the sky. This method, 

 as he explained, has several advantages over the ordinary 

 sundial. Wheatstone's spectroscopic observations and his 

 contributions to telegraphy will be referred to in another 

 place (see pp. 154, 188). 



The first sight that meets the eye of a visitor entering 

 the Town Hall of Manchester is the statue of Dalton on 

 his left, and that of Joule on his right. These two great men 

 found a congenial home in the town which numbered amongst 

 its citizens others who, long before it became the seat of a 

 University, upheld the dignity and usefulness of its Literary 

 and Philosophical Society. Such were Thomas Henry (1734- 

 1816), the author of valuable investigations in Chemistry; 

 his son, William Henry (1774-1836), who studied the laws 

 of absorption of gases by liquids, and William Sturgeon 

 (17831850), the inventor of the electro -magnet, who started 

 life as a shoemaker, entered the army as artillerist, became 

 teacher of physics at the military academy of the East India 

 Company, and spent the last twelve years of his life in 

 scientific investigations at Manchester. The ambition of that 

 town to become the seat of a University dates back .to the 

 seventeenth century, and though renewed at various times 

 long remained unsatisfied. By the will of John Owens, who 

 died in 1850, a college was founded, which after a period 

 of difficulty rapidly rose to eminence. It numbered among 

 its first professors Edward Frankland (1825-1899), whose 

 researches were fundamental in the development of modern 

 chemistry, and who, next to Davy and Dalton, must pro- 

 bably be considered to be the greatest chemist this country 

 has ever produced. Having discovered a number of organic 

 substances containing metallic atoms as essential consti- 

 tuents, he investigated the general laws of the formation of 

 chemical compounds, and originated the conception that 

 the atom of an elementary substance can only combine with 

 a certain limited number of atoms of other elements. This 

 led to the discovery of " valency " as the groundwork of 



