Natural Histonj. 197 



Modern times have given birth to various in- 

 ventions for measuring the force and velocity of 

 winds. Among these the most remarkable are the 

 Wind-gage, the Anemoscope, and the Anemometer; 

 in the construction and improvement of which 

 Dr. Linn, Mr. Pickering, and others, have ren- 

 dered important service to meteorology. Numer- 

 ous attempts have also been made, during the 

 period under review, to construct hygrometers , or 

 instruments for indicating the comparative states 

 of the atmosphere, with respect to moisture and 

 dryness. And though mLK:h imperfection is found 

 to attend every instrument hitherto devised for this 

 purpose, yet gradual approximations have been 

 made toward those of a more perfect and useful 

 kind. Among these Mr. Smeaton's hygrometer^ 

 formed of an hempen cord, boiled in salt water; M. 

 DeSaussure's, made of hair, prepared by macera- 

 tion in alkaline ley; Mr. Coventry's, consisting 

 of dryed paper-, and M. De Luc's, of ivory and 

 ivhalebone, deserve to be distinguished; especially 

 that formed of ivhalelwne by A'l. De Luc, which 

 is generally considered as the most accurate and 

 convenient hygrometer now in use. 



That remarkable meteorological phenomenon, 

 usually called the Aurora Borealis, appeared with 

 peculiar frequency, in the course of the eighteenth 

 century. Dr. Halley tells us^ that it was seen 

 but once in the seventeenth century, viz. in 1621, 

 w^hen it attracted considerable attention, particu- 

 larly in France, where the celebrated Gassendi 

 (^)bserved it, and gave it the name which it now 

 bears. After this there is no record of any such 

 appearance until 1707, when a small one was seen. 

 But in 17 1 6 an uncommonly brilliant one appeared, 

 which commanded universal attention, and was 



j Philosophical Transactions, No. 347. 



