464 



LECTURE XLIX. 



ON THE ESSENTIAL PROPERTIES OF MATTER. 



THE objects, which have lately occupied our inquiries, are the most 

 sublime and magnificent that nature any where exhibits to us, and the 

 contemplation of them naturally excites, even in an uncultivated mind, an 

 admiration of their dignity and grandeur. But all magnitude is relative ; 

 and if we examine with more calm attention, we shall find still greater 

 scope for our investigation and curiosity, in the microscopic, than in the 

 telescopic world. Pliny has very justly observed, that nature no where 

 displays all her powers with greater activity, than in the minutest objects 

 perceptible to our senses ; and we may judge how wide a field of research 

 the corpuscular affections of matter afford, from the comparatively small 

 progress that has hitherto been made in cultivating it. For while the 

 motions of the vast bodies, which roll through the heavens, have been 

 completely subjected to the most rigorous calculations, we know nothing, 

 but from experience only, of the analogies by which the minute actions of 

 the particles of matter are regulated. It is probable, however, that they 

 all depend ultimately on the same mechanical principles. We have seen, 

 for example, that the widely extended elevations and depressions of the 

 ocean, which are raised by the attractive powers of the two great lumina- 

 ries, and cover at once a half of the globe, are governed and combined 

 according to the same laws which determine the motions of the smaller 

 waves excited by different causes in a canal, the rapid tremors of a medium 

 transmitting sound, or the inconceivably diminutive undulations which 

 are capable of accounting for the phenomena of light, and which must be 

 exerted in spaces as much smaller than those of sound, as a grain of sand 

 is smaller than a mountain. Thus the annihilation of the effects of the 

 semidiurnal changes of the tide, and the preservation of the diurnal change, 

 in the harbour of Batsha, may be explained precisely in the same manner 

 as the reflection of red light from a transparent substance, of such a thick- 

 ness, as to be capable of destroying a portion of violet light under the same 

 circumstances. 



We are at present to descend from the affections of the large masses of 

 matter, which form the great features of the universe, to the particular 

 properties of the matter which constitutes them, as far as they are common 

 to all matter in general ; but those properties which are peculiar to certain 

 kinds of matter only, being the subjects of chemical science, are not to be 

 included in the discussion. If we are asked for a definition of matter, it 

 will be somewhat difficult to avoid all circuitous expressions. We may 

 make gravitation a test of matter, but then we must say, that whatever is 

 attracted by other matter, is also to be denominated matter, and this sup- 

 poses the subject of our definition already known ; besides that the property* 

 of attraction may also possibly belong to substances not simply material ; 



