INTRODUCTION. xiii - 



This forms what may very properly be termed VEGETABLE GEOGRAPHY, a very interesting 

 :iml important department of natural history, but one which has not hitherto been treated 

 of separately to the extent which its importance requires. Thirdly, the seasonal changes 

 which take place in the appearance of plants, and which, as has been remarked, constitute 

 the "-rand index to the revolving year, and which has not yet received a name as a distinct 

 branch of science. 



The two last-mentioned divisions are intimately connected with each other ; because 

 plants are influenced by climate only so far as that climate produces season ; and if they 

 had the same season, or the same succession of seasons, all climates would be alike. 



The "-eneral circumstances, whether we call them of a climatal or a seasonal nature, by 

 which plants are influenced, are humidity, heat, and light; wherever these occur to the same 

 extent the action of any one vegetable may be presumed to be the same. It is usual to refer 

 the origin of heat generally to the sun ; and though that body is not the source cf all heat, 

 and perhaps would not be the source of any without something upon which its beams could 

 act, vet the heat of the sun is that by which vegetables in a state of nature, and even as 

 cultivated, are the most generally influenced. The light of the sun is also the principal and 

 perhaps the only light which has a general influence on vegetable action. No satisfactory 

 experiments have been made to show what might be the effect of artificial lights on vegetables ; 

 and though moonlight produces some effects, they appear to tend to ripening rather than to 

 growth. That might be expected, as the light of the moon wants the extreme rays of the 

 solar spectrum, and especially those chemical rays which lie invisibly beyond each extremity 

 of the colours, and which so curious.lv link together the polarities of atoms, the phenomena 

 of magnetism, galvanism, electricity, vegetable action, and probably all the phenomena of 

 matter to which the name of action can be applied. 



As, however, separate treatises on the various branches of physical science would be out 

 of place in a work expressly devoted to the study and illustration of natural history, the 

 reader will, in every instance, be referred to those articles in the first division of the Cyclo- 

 paedia, where they are fully examined. The classification of plants as much as possible 

 according to their organisation, will be found in the general article BOTANY ; and the process 

 of vegetation, its nature, and its results, as forming both the component and the constituent 

 parts of plants, will be treated of under the various articles belonging to VEGETABLE 

 PHYSIOLOGY. 



THE MINERAL KINGDOM. 



THIS division, or kingdom, of nature, comprehends all the unorganised parts of the 

 earth : but it may be advantageously subdivided ; for, without any reference to their 

 chemical properties, which are fully illustrated in the First Division of this work, mineral 

 substances may be viewed in two distinctly different lights, first, in themselves considered 

 individually ; and, secondly, in their relations to each other and to the whole earth, both in 

 its present state and its past history. 



Both of these are parts of natural history ; but the first of them belongs more to 

 descriptive detail, and the second more to theoretical conjecture. The knowledge of the 

 first is the science of MINERALOGY, and that of the second is the science of GEOLOGY. 



Geology, though of late years it has made rapid progress, is still only in its infancy, so 

 that, though there are many interesting facts, there can be said to be no general system. The 

 general purpose of the science is to examine the whole surface of the earth, and as far 

 below that surface, whether dry land or water, as observation can go; to ascertain the form, 

 nature, and arrangement of the several parts ; and to point out, if possible, by what agents 

 and in what manner, they were brought into their present state and situation. Climates 



