ANNALS 



or 



PHILOSOPHY. 



JULY, 1820. 



Article I. 



HISTORICAL SKETCH OF IMPROVEMENTS IN PHYSICAL 

 SCIENCE DURING THE YEAR 1819. 



]. The Chemical Sciences. By Thomas Thomson, M.D. F.R.S» 



Of all the sciences which require the aid of experiment, there 

 is none which embraces so vast a field, and which of course 

 requires so many cultivators, as chemistry. Its object is ta 

 determine the composition of all the substances in nature whether 

 mineral, vegetable, or animal, to ascertain the simple bodies of 

 which they are composed, and to determine the laws by which 

 the union of these simple bodies is regulated. From the vast- 

 ness of the field, and tlie comparatively short period of the exist- 

 ence of chemistry as an analytical science, which can scarcely 

 be reckoned longer than 60 years, it is not to be expected that 

 great progress can have been made in the exact knowledge of 

 the composition of bodies as they exist in the various kingdoms 

 of nature. The constituents of the atmosphere and of water are 

 perhaps as accurately known as those of any other body what- 

 ever ; yet even in these comparatively simple inquiries, there are 

 several points which still remain to be determined. Thus the 

 most accurate experiments hitherto made induce us to conclude 

 that air is a compound of 21 volumes of oxygen gas and 79 

 volumes of azotic gas ; yet the atomic theory requires the con- 

 stituents to be 20 volumes of oxygen and 80 of azote. We have 

 no conception whatever respecting the nature or properties of 

 the contagious matters, which are supposed occasionally to mix 

 with the air, and to induce certain diseases iiito living beings. 

 Vol. XVI. NM. A 



