SEVENTEENTH AND EIGHTEENTH CENTURIES 153 



orders in the Church of England. He held various posts and finally became 

 vicar of Teddington, a parish in Middlesex, where he died in 1761. He was 

 known as a zealous priest, who worked for the advancement of his parish 

 from both a moral and a material point of view, and besides found time to 

 devote himself to important philanthropical works, such as the improve- 

 ment of prison conditions, the administration of charitable societies, and 

 inventions likely to prove of benefit to mankind. By those who knew him 

 personally he was extolled for his kindness and simplicity. 



At Cambridge Hales had been attracted to the study of natural science, 

 particularly physics, chemistry, and botany; indeed, during his undergrad- 

 uate days Cambridge was primarily regarded as Newton's town. He main- 

 tained this interest throughout his life; it thus occurred to him to try by 

 way of physics to discover the conditions of the life and growth of plants, 

 an idea that he realized after experimental studies lasting many years. He 

 published his results in the year 1717 under the title of Vegetable Staticks. 

 In his ability to organize biological experiments and to draw conclusions 

 therefrom he was excelled by none of his contemporary scientists and by 

 but few of those that have come after him; it has been possible even in mod- 

 ern times to apply his experimental methods with profitable results. In re- 

 gard to his general cosmic conceptions Hales was, naturally, in conformity 

 with his profession and his age, a pious Christian, but like his master Newton 

 he strove conscientiously to discover the law-bound mechanical processes 

 undergone by the phenomena be investigated; he would never involve him- 

 self in hypothetical explanations of the manifestations of life. 



Hales' s quantitative experiments 

 What Hales wished to discover by means of his experiments was, first of 

 all, the renewal of substance in plants, both quantitatively and qualitatively. 

 It is above all his quantitative investigations that merited and also won 

 general admiration; he was the first to apply systematically and on a large 

 scale the exact method of physics to animate nature. By watering previously 

 weighed potted plants for a given length of time with a fixed quantity of 

 water, and by weighing the plant daily during that period, he found out 

 its water-consumption; then he measured the leaf- and stem-surface of the 

 plant and calculated therefrom the relation between the surface of the plant 

 and the quantity of w^ater that it absorbed daily. Similarly, by means of 

 measuring and weighing he calculated the quantity of moisture that differ- 

 ent plants absorb out of the earth through their roots, as well as the speed 

 with which the sap circulates in the interior of the plant; and finally he 

 proved that plants absorb air through their leaves and stems and not only 

 through their roots, as earlier botanists declared. He was quite specially 

 interested in the problem of the relation of the air to living creatures. He 

 definitely maintains that the air contains component parts which are ab- 



