460 LECTURE XLIX. 



shall touch either of them, except at the general point of contact ; and that 

 a ship, following always the same oblique course with respect to the meri- 

 dian, for example, sailing north eastwards, would continue perpetually to 

 approach the pole without ever completely reaching it. But when we 

 inquire into the truth of the old maxim of the schools, that all matter is 

 infinitely divisible, we are by no means able to decide so positively. New- 

 ton observes, that it is doubtful whether any human means may be suffi- 

 cient to separate the particles of matter beyond a certain limit ; and it is 

 not impossible that there may be some constitution of atoms, or single 

 corpuscles, on which their properties, as matter, depend, and which would 

 be destroyed if the units were further divided ; but it appears to be more 

 probable that there are no such atoms ; and even if there are, it is almost 

 certain that matter is never thus annihilated 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 -jnjVu- of an inch in diameter ; by the assistance of a 

 microscope, we may perhaps distinguish a body one hundredth part as 

 large, or ir ^^ rjra . of an inch 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 -jV^ 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.t 

 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 remark- 

 able, 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 simple as 

 they deviate more from the form of quadrupeds, and from that of the 

 human species ; 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 among the microscopic 

 insects in particular, 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 appears 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 in general, were sufficiently established, it would afford us a limit 



* Consult Wollaston, Ph. Tr. 1822. 



t SeeHalley, Ph. Tr. 1693, p. 540. Nicholson, ibid. 1789, p. 286. Button's 

 transl. of Montucla's Mathematical Recreations, 4 vols. Lond. 1803, vol. iv. p. 80. 



