Ornithology. 295 



not be approached by other means. It has been apphed to this 

 latter purpose in at least one, if not more instances, by the French 

 engineers, dm-ing the late war. But who can undertake to assign 

 thehmits beyond which the ingenuity and the enterprise of man shall 

 not pass ? Though this species of navigation labors under diffi- 

 culties which appear at present insurmountable ; though the want 

 of some means to control and regulate the movements of the aeri- 

 al vessel is so essential as to excite a fear that it cannot be sup- 

 plied ; yet who can tell what further experience and discoveries 

 may produce ? Who can tell but another century may give rise 

 to such improvements, that navigating the air may be as safe, as 

 easy, and rendered subservient to as many practical purposes as 

 navigating the ocean ? It must be acknowledged, indeed, that 

 tliis is not very probable ; but things more unexpected, and more 

 remote from our habits of thinking, have doubtless occurred. 



ORNITHOLOGY. 



NO. IX. 



Migration of Birds. Birds without the means of convey- 

 ing themselves with great swiftness from one place to another, 

 could not easily subsist with the food which nature has provided for 

 them, being so irregularly distributed that they are obhged to take 

 long journeys to distant parts, in order to procure the necessary 

 supplies. Hence one cause of those migrations which are so pe- 

 culiar to the feathered race. Besides the want of food, however, 

 two other causes may be assigned, namely, the want of a proper 

 temperature of air, and of a convenient situation for the important 

 work of breeding their young. Such birds as migrate to great 

 distances are denominated birds of passage ; but most species are 

 more or less so, although they do not move to places remote from 

 their former habitations. At particular periods of the year, most 

 birds remove from one country to another, or from the more in- 

 land districts towards the shores, or vice versa. The seasons of 

 these migrations are observed with the most astonishing regularity, 

 and punctuality ; but the secrecy, with which immense flocks 

 take their departure, and the suddenness with which they appear, 

 are not easily explained. 



