ON VEGETATION. 665 



far enough into the atmosphere to produce an appearance of light, re- 

 sembling that of a shooting star ; but it is scarcely probable that their 

 velocity could ever be at all comparable with that which has been attri- 

 buted to these meteors. There is, however, no difficulty in supposing, on 

 the other hand, that the wandering substances, which may be moving 

 through empty space, with a velocity equal to that of the shooting stars, 

 may be so much retarded, when they penetrate deep into our atmosphere, 

 as to make but a moderate impression by their fall on the ground ; and if 

 we suppose the meteors to be of one kind only, they must be referred 

 rather to the description of shooting stars than to that of the productions 

 of lunar volcanos; although the undulatory motion, sometimes observed in 

 these meteors, seems to be in some measure inconsistent with the progress 

 of a heavy body, moving by means of its natural inertia in a straight line. 



LECTURE LVIII. 



ON VEGETATION. 



IT may appear idle to some persons, to attempt to reduce the outlines 

 of natural history into so small a compass, as is required for their becom- 

 ing a part of this course of lectures ; and it would indeed be a fruitless 

 undertaking to endeavour to communicate a knowledge of the particular 

 subjects of this science, even in a much longer time than we shall bestow 

 on it. But many naturalists have spent a great portion of their lives in 

 learning the names of plants and animals, and have known at last less of 

 the philosophy of the science, than might have been told them in a few 

 hours, by persons who had observed with more enlarged views, and who 

 had reasoned on general principles. And we shall perhaps find it possible 

 to collect into a small compass the most useful information, that has 

 hitherto been obtained, respecting the laws of animal and vegetable life, as 

 well as the foundations of the methods, by which the most received syste- 

 matical classifications have been regulated. 



The surface of the earth, as well sea as land, is occupied by innumerable 

 individuals, constituting an immense variety of distinct species of animated 

 and inanimate beings, comprehended in the three grand divisions of natural 

 bodies. The mineral kingdom consists of such substances as are composed 

 of particles either united without any regular form, or collected together by 

 accretion or external growth only. When mineral substances crystallize, 

 they often imitate the form, and almost assume the external appearance of 

 vegetables : but their particles are never extended to admit others between 

 them, aad to be thus enlarged in all their dimensions ; their growth is only 

 performed by the addition of similar particles, upon the surface of those 

 that have been already deposited. 



