Robert Boyle 75 



of Christianity. He was never strong in health; weak 

 eyesight troubled him throughout life, and a painful disease 

 caused him much suffering in later years. 



His scientific work is distinguished by great experi- 

 mental skill, and a determination to remain free from the 

 bias of preconceived notions. In his travels he had 

 become proficient in several languages, and he continued 

 to keep himself informed of what was being done on the 

 continent of Europe. Having read an account of Guericke's 

 air-pump (or, as Boyle calls it, " wind-pump "), he set 

 to work to construct one, and with the help of Robert 

 Hooke, who appears to have acted as his assistant at that 

 period, succeeded in effecting considerable improvements. 

 With this pump a large number of experiments were per- 

 formed, all devised to prove some definite point, such as 

 comparing the weight of air with that of water, or inves- 

 tigating what he calls the spring of air. He showed that 

 flames are extinguished and hot coal ceases to glow in a 

 partial vacuum. He proved that magnetic and electric 

 actions persist in his exhausted receiver, and that warm 

 water begins to boil under reduced pressure. The action 

 of the pump in removing air from a vessel suggested the 

 inverse process of increasing the pressure, and this led to 

 the construction of the compression pump. In his measure- 

 ments he attained considerable accuracy; the specific 

 gravity of mercury was correctly determined to one half 

 per cent., that of air to about 20 per cent. 



Boyle's name is associated with the important law 

 connecting the density of air with its pressure. The proof 

 of the law is contained in a long paper entitled " Defence 

 of the doctrine touching the spring and weight of air," 

 published in 1662. The range of pressures covered by the 

 experiments extended from four atmospheres (involving 

 the use of glass tubes ten feet long) down to 1J inches of 

 mercury; the agreement between observed pressures and. 

 those calculated from the changes of volume, assuming that 

 density and pressure are proportional, was quite sufficient 

 to prove the correctness of the law. The often repeated 

 assertion that it was Townley who first drew Boyle's 

 attention to the significance of these observations and for- 



