748 LECTURE LX. 



and it was not till the close of the century, that Dr. Ilooke's discovery, of the 

 permanency of the temperature of boiling water, afftnded a correct and con- 

 venient limit to the scale on one side, M'hile the melting of snow served for 

 fixing a similar point on the other; although there would have been no 

 great difficulty in forming a scale sufficiently natural, from the proportion 

 of the expansion of the fluid contained in the thrrnomeeter to its whole 

 bulk. ' 



It was about the year 1628, that Dr. Harvey succeeded in demonstrating, 

 by a judicious and conclusive train of experiments, the true course of the 

 circulation of the blood, through the veins and arteries, both in the perfect 

 state of the animal, and during its existence as an embryo. Servetus had 

 explicitly asserted, in his work on the Trinity, as early as the year 1553, 

 that the blood performed, in its passage through the" lungs, a complete re- 

 volution, beginning and ending in the heart ; and Cisalpinus had even expressed, 

 in 1569, some suspicions that the circulation of the whole body was of a 

 similar nature; but neither of these authors had advanced any satisfactory 

 proofs in confirmation of his opinions. 



In the middle of the seventeenth century, the barometer was invented by 

 Torricelli; the variation of the atmospheric pressure was discovered by 

 Descartes; and Pascal made several experiments on the difference of its 

 magnitude at different places, which tended to illustrate the principles, on 

 "which the method of determining heights by barometrical observations is 

 founded. 



What Gesner and Aldrovandus had before done with regard to the animal 

 kingdom, was performed, a century later, for the vegetable world by John 

 and Caspar Bauhin, whose works, as collections of all that was to be found on 

 record respecting the distinctions and properties of plants, have not yet been 

 superseded by the latest publications. Our countrymen, Ray and Willughby, 

 contributed also to add much new matter to the stores of natural history, 

 in all its departments; and their labours, as well as those of Tournefort and 

 Reaumur, are of the more value, as they were far more studious than their 

 predecessors to discriminate truth from fiction. 



