198 Natural HlstoTx). 



considered by the vulgar as a most portentous 

 event. Since that time these meteoric pheno- 

 mena have been so frequent and familiar, that they 

 have, in a great measure, ceased to attract atten- 

 tion, or to be recorded as remarkable events. 



Modern philosophers have ascertained many 

 facts v^^ith respect to the Aurora Borealis, which 

 were, of course, unknown to those who lived in 

 the seventeenth century, and probably to all who 

 lived before them. It seems now to be generally 

 considered either as an elect j^ical phenomenon, or 

 produced by the combustionof inflammable air, either 

 with or without the intervention of the electric 

 spark. For the observations which have been 

 made upon this kind of meteor, and the principles 

 with respect to it which appear to be established, 

 we are under particular obligations to Dr. Hal- 

 XEY, M,. Mairan, Signor Beccaria, Dr. Frank- 

 i>iN, Dr. Forster, M. Gmelin, M. ^pinus, Dr. 

 Hamilton, of Dublin, Mr. Canton, Dr. Blag- 

 den, Mr. Dalton, and others. The last named 

 gentleman is supposed to have given the most sa- 

 tisfactory account of the subject. 



hydrology. 



The natural history of Waters holds so important 

 a place among the objects of human knowledge, 

 that it has, in almost every age, attracted the at- 

 tention of those who loved to study nature: but 

 it is only within the century under review that 

 any thing on this subject, deserving the name of 

 science, or a correct acquaintance with principles, 

 could be said to exist. The accessions to Hy- 

 drology in modern times have been very great. 

 The improvements in Chemistry, in Mineralogy, 

 and in manv other sciences, have contributed much 



