«rct. ii.] DISSERTATION SECOND. 65 



trade-wind, and the monsoons, together with many inte- 

 resting facts concerning the phenomena of the tides. The 

 chart which contained an epitome of all these facts was pub- 

 lished in' 1701. 



The above are only a part of the obligations which the 

 sciences are under to the observations and reasonings of this 

 ingenious and indefatigable inquirer. Halley was indeed 

 one of the ablest and most accomplished men of his age. 

 A scholar well versed in the learned languages, and a ge- 

 ometer profoundly skilled in the ancient analysis, he res- 

 tored to their original elegance some of the precious frag- 

 ments of that analysis, which time happily had not entire- 

 ly defaced. He was well acquainted also with the alge- 

 braical and fluxionary calculus, and was both in theory 

 and practice a profound and laborious astronomer. Fi- 

 nally, he was the friend of Newton, and often stimulated, 

 with good effect, the tardy purposes of that great philo- 

 sopher. Few men, therefore, of any period, have more 

 claims than Halley on the gratitude of succeeding ages. 



The invention of the thermometer has been already 

 noticed, and the improvements made on that instrument 

 about this period, laid the foundation of many future dis- 

 coveries. The discovery of two fixed temperatures, each 

 marked by the same expansion of the mercury in the 

 thermometer, and the same condition of the fluid in which 

 it is immersed, was made about this time. The differen- 

 ces of temperature were thus subjected to exact measure- 

 ment; the phenomena of heat became, of course, known 

 with more certainty and precision ; and that substance or 

 virtue, to which nothing is impenetrable, and which finds 

 its way through the rarest and the densest bodies, appa- 

 rently with the same facility, — which determines so many 

 of our sensations, and of which the distribution so mate- 

 rially influences all the phenomena of animal and vegeta- 







