608 LECTURE XLIX. 



constitution of atoms, or single corpuscles, on which tbeir properties, as 

 matter, depend, and which would be destroyed if the units were further 

 divided; but it appears to be niOre probable that there are no such atoms; 

 and even if there are, it is ahnost certain that matter is never thus annilii- 

 lated in the common course of nature. 



It remains to be examined how far we have any experience of the actual extent 

 of the divisibility of matter; and we shall find no appearance of any thing like 

 a limit to this property. The smallest spherical object, visible to a good eye, is 

 about v o' oo- of an inch in diameter; by the assistance of a microscope, we may 

 perhaps distinguish a body one hundredth part as large, or^-^^'-o-^-o of aninch 

 in diameter. The thickness of gold leaf is less than this, and the gilding of 

 lace is still thinner, probably in some cases not above one ten millionth of an 

 inch ; so that -^-^^ of a grain would cover a square inch, and a portion, barely 

 large enough to be visible by a microscope, might weigh only the 80 million 

 millionth part of a grain. A grain of musk is said to be divisible into 320 

 quadrillions of parts, each of which is capable of affecting the olfactory 

 nerves. There are even living beings, visible to the microscope, of which a 

 million million would not make up the bulk of a common grain of sand. 

 But it is still more remarkable, that, as far as we can discover, many of 

 these animalcules are as complicated in their structure as an elephant or a 

 whale. It is true that the physiology of the various Classes of animals is 

 somewhat more sinlplc as they deviate more from the form of quadrupeds, 

 and from that of the human sjjecies ; the solid particles of the blood do not 

 by any means vary in their magnitude in the same ratio with the bulk of the 

 animal; and some of the lower classes appear to approximate very much to 

 the nature of the vegetable world. But there are single instances that seem 

 wholly to destroy this gradation : Lyonnet has discovered a far greater variety 

 of parts in the caterpillar of the willow butterfly, than we can observe in many 

 animals of the largest dimensions ; and amofig the microscopic insects in par- 

 ticular, we see a prodigality of machinery, subservient to the various purposes 

 of the contracted life of the little animal, in the structure of which nature ap- 

 pears to be ostentatious of her power of giving perfection to her minutest works. 



If Newton's opinion, respecting the origin of the colours of natural bodies 

 III general, were suificieutly established, it would afford us a limit to the dl- 



