Stephen Hales 237 



but an active researcher in animal physiology. He, in fact, 

 introduced into both fields of Physiology the process of 

 weighing and measuring. His experiments on the loss of 

 water which plants suffered by evaporation and on the 

 absorption of water by roots are classic, and still remain 

 of the greatest importance. His suggestion that the ascent 

 of the sap is not from the roots only but must proceed from 

 some power in the stem and branches, has recently met with 

 a certain amount of corroboration. He introduced a new 

 method by ever seeking a quantitative knowledge of the 

 various physiological functions he was enquiring into. He 

 experimented on the amount of rain and dew on special 

 areas of the ground, and on the expansive force that peas 

 exhibit when they absorb water, and explained variations 

 in pressure from hour to hour on the rate of growth of the 

 various members of the plant-organism, and aU by methods 

 which are still in use. He was one of the first to oppose 

 the older views on the circulation of sap views which had 

 certainly retarded progress and at any rate he had some 

 inkling that air is a source of food to plants. He also had 

 a clear idea of the importance of scientific knowledge in its 

 practical application to agriculture. Without any doubt, 

 the Englishman Hales must be regarded as the founder of 

 that very important science, Plant Physiology. 



Hales was a man of many inventions, and he devoted 

 his extraordinary ingenuity largely to improving the lot 

 of oppressed mankind. He invented various artificial 

 ventilators which were used in granaries, ships, and prisons, 

 and, so far as one can make out, the health of the prisoners 

 greatly benefited by the introduction of his appliances. 

 He also experimented on the distillation of salt water to 

 make it fresh, on the preservation of various forms of food 

 for sea voyages, on methods for cleaning harbours, and he 

 devised an instrument for deep-sea dredging which, together 

 with a large number of other mechanical contrivances, 

 occupied his ever active mind. 



Hales was evidently a lovable, kindly character, and 

 without doubt was the greatest physiologist of his age, and 

 of many later ages. 



One other man of science, although not a botanist, must 



