84 Britain's Heritage of Science 



one of the richest men of his time, without altering the simple 

 mode of life to which he had become accustomed. It has 

 been said of him that his chief object in life was to avoid 

 the attention of his fellows; " his dinner was ordered daily 

 by a note placed on the hall-table, and his women servants 

 were instructed to keep out of his sight on pain of dismissal." 1 



There is some evidence, however, that in his intercourse 

 with scientific men he was not equally reticent. He attended 

 the meetings of the Royal Society regularly, dined nearly every 

 Thursday with the Philosophical Club, composed of some 

 of the Fellows, and in 1772 was an energetic member of a 

 committee formed to consider the best means of securing a 

 powder magazine against the danger of lightning. 



Some of Cavendish's most remarkable results were de- 

 rived from experiments on gases. Such investigations then 

 tested the skill of an experimenter to a degree which is not 

 easily realized at present. To the difficulties of isolating, 

 purifying, and examining the chemical properties of these 

 invisible substances was added the mystifying belief in the 

 imaginary body, phlogiston, which was supposed to be 

 expelled in every act of combustion, and to account for 

 flame and fire. 



From the purely experimental point of view a great 

 advance was made when gases were collected over mercury 

 instead of over water, which had been the usual practice. 

 The credit of this is due to Joseph Priestley (1733-1804), a 

 Nonconformist minister, who, having renounced his early 

 Calvinism and become a Unitarian, was then in charge of 

 Mill Hill Chapel, Leeds ; subsequently he moved to Birming- 

 ham. Priestley held strong political views, which he expressed 

 freely, and these, together with his unorthodox opinions, 

 frequently got him into trouble. He wrote against England's 

 attitude towards the American colonies, and sympathized with 

 the French revolutionists. When he attended a dinner 

 arranged to celebrate the anniversary of the taking of the 

 Bastille, the mob burned his chapel and sacked his house. 

 He then went to live in London for a few years, but ultimately 

 emigrated to America. We owe to Priestley the discovery of 



1 " Encyclopaedia Britannica." 



