76 Britain's Heritage of Science 



mulated the law is not justified, and is founded apparently 

 on some misconception of a passage in Boyle's account of 

 his experiments. 



We owe to Boyle the use of the term " barometer," 

 and he constructed an instrument in which the mercury 

 is replaced by a short column of water with sufficient air 

 above to counter-balance the atmospheric pressure. When 

 no temperature changes interfere, such an instrument 

 would be considerably more sensitive than an ordinary 

 barometer. With it Boyle could observe the difference of 

 pressure between the roof and floor of Westminster Abbey, 

 thus confirming Pascal's experiment without having to 

 ascend a mountain. 



In his optical experiments Boyle showed that colours 

 are produced by a modification of the light which takes place 

 at the surface of the coloured body. The connexion between 

 radiant heat and light was illustrated by covering half of a tile 

 with black and the other half with white paint, when he 

 found that in sunlight the black paint becomes hot while 

 the white remains cold. He also first drew attention to the 

 colours of thin films such as soap bubbles. He investigated 

 freezing mixtures and discovered that when salt is added to 

 snow or ice the observed cooling is connected with the lique- 

 faction of the salt. Boyle invented the hydrometer and 

 showed how to determine by means of it specific gravities not 

 only of liquids but also of solids. He made extensive chemi- 

 cal experiments, and correctly explained a chemical reaction 

 as being due to the substitution of an atom of one kind for 

 an atom of another kind in the original compound. 



Boyle's completed works occupy six folio volumes; 

 he is somewhat prolix in his discussions, but his descrip- 

 tions are always clear and interesting. By the manner 

 in which he allows himself to be led from one experiment 

 to another he almost reminds one of Faraday, though his 

 indiscriminate mixing of what is important with what is 

 of minor value partakes a little of the weakness of the 

 dilettante. He was highly esteemed by his contemporaries, 

 and Newton, as well as many other eminent men of science, 

 showed, in their correspondence, that they attached great 

 value to his opinions. 



