326 ON MATERIALISM 



Let us take a single example of this curious phenomenon, and let 11 .*aw 

 it from facts that are known to almost every one. The water of the s^ 4, and 

 of various land-springs, as that at Epsom, for example, is loaded with a 

 certain portion of sulphuric acid, or oil of vitriol; thus impregnated, as it 

 flows over a soil composed either wholly or in part of the earth called 

 magnesia, it evinces a peculiar attraction for this substance, separates it from 

 the bed on which it has been quietly reposing 1 , and so minutely dissolves it, 

 as still to retain its transparency. But the attraction of the sulphuric acid 

 for the magnesia is much less than its attraction for the fixed alkalies, potash 

 and soda : and hence, if to the water thus impregnated we add a certain 

 quantity of either of the two latter substances, the connexion between the 

 acid and the magnesia will immediately cease : the former will evince its- 

 preference for the alkali employed ; and the magnesia, no longer laid hold of 

 by the sulphuric acid, will be precipitated, or, in other words, fall by its own 

 weight to the bottom of the water, in the form of a white powder, and maybe 

 easily collected and dried. And this, in reality, is the usual mode by which 

 this valuable earth is obtained in its pure state. 



But the sulphuric acid having thus shown a stronger attraction for an alkali 

 than for an earth, is there no substance for which it discovers a stronger at- 

 traction than for an alkali ! There are various : it may be sufficient to men- 

 tion caloric or the matter of heat. And hence, exposed to the action of heat, 

 it soon becomes volatile, unites itself to the heat, flies off with it in vapour, 

 and now leaves the alkali behind as it before left the magnesian earth. 

 Glass-manufacturers take advantage of this superior attraction of the mine- 

 ral acids for heat compared with their attraction for alkalies, and employ, in 

 their formation of glass, common sea-salt, which is a combination of an acid 

 and an alkali ; drive off the former from the latter by the aid of a very pow- 

 erful fire, and then obtain a substance which is absolutely necessary for the 

 production of this material. 



These curious and altogether inexplicable properties and preferences we 

 call chemical affinities and chemical elections : and there are numerous in- 

 stances in which the substances, thus uniting themselves together, evince an 

 order and regularity of the most wonderful precision, and which is nowhere 

 exceeded in the developement of the most delicate organ of animated nature. 

 And I now particularly allude to the phenomena of crystallization; the dif- 

 ferent kinds of which, produced by the consolidation of different substances, 

 uniformly maintain so exact an arrangement in the peculiar shape of the 

 minute and central nucleus, or the two or three elementary particles that first 

 unite into a particular figure, and follow up with &o much nicety the same 

 precise and geometrical arrangement through every stage of their growth, 

 that we are able, in all common cases, to distinguish one kind of crystal from 

 another by its geometrical figure alone ; and with the same ease and in the 

 same manner as we distinguish one kind of animal from another by its gene- 

 ral make or generic structure. The form of these elementary particles we 

 can no more trace to a certainty than the bond of their union ; but there is 

 great reason for believing them to be spheres or spheroids, as first conjectured 

 by that most acute and indefatigable philosopher Dr. Hooke, and since at- 

 tempted to be explained by Dr. Wollaston in a late Bakerian lecture.* 



Such are the most striking powers that occur to us on a contemplation of 

 the unorganized world. From unorganized let us ascend to organized 

 nature. And here the first peculiar property that astonishes us is the princi- 

 ple of life itself; that wonderful principle equally common to plants and 

 animals, which maintains the individuality, connects organ with organ, resists 

 the laws of chemical change or putrefaction, which instantly commence 

 their operation as soon as this agent or endowment ceases ; and which, with 

 the nicest skill and harmony, perpetuates the lineaments of the different kinds 

 and species through innumerable generations. It is an agency which exists 

 as completely in the seed or the egg as in the mature plant or animal : for as 



* Phil. Trans. 1813, p. 51. 



