58 Mechanical Philosophy, [Chap. I, 



in exploring this dark recess of philosophy, still 

 greater advances in our knowledge of it may soon 

 be expected. For some instructive publications on 

 this subject, we are indebted to Dr. Halley, and 

 Mr. Dalton, of Great Britain ; Mr, Kirwan, of Ire- 

 land ; and Messrs. de Luc and Prevost, of Geneva. 

 Various instruments, which answer valuable pur- 

 poses for measuring the direction, the force, and 

 the velocity of winds, have also been invented, 

 within a few years past, by Dr. Linn, Mr. Picker- 

 ing, and others of Great Britain. These inven- 

 tions have been denominated the Jnetnoscope, the 

 Anemometer, &c. 



Finally, the doctrines of Acoustics have been 

 very successfully illustrated, since the time of 

 Newton, by various inquirers. Many facts re- 

 lating to the velocity, the intenseness, and the ge- 

 neral principles of sounds, have been established 

 by numerous experiments. The capacity of dif- 

 ferent bodies to propagate sound has become 

 better understood by the investigations of modern 

 philosophers. Mr, Hawksbee, of Great Britain, 

 first showed that sound is propagated further in 

 dense than in rarefied air ; M. Brisson, of France, 

 and others, demonstrated, by various interesting 

 experiments, that a medium more dense than air 

 conveys sound still better than this fluid; and Dr. 

 Young, of Dublin, has, within a few years, made 

 some new and instructive inquiries into the prin-. 

 ciples of acoustics. To which may be added the 

 interesting experiments lately made, showing the 

 different intensity, and the variety of tones of 

 sound, in different gases, by several philosophers. 



That the different gases have different degree^ 



