mind receives ideas, which agree in fome but differ in other parts, it then separates the parts which agree from those which do not; and the fimple idea becomes a complex one; thefe may be called complex in their nature or substances: arbitrary ones are formed by adding feveral fimple ideas together.

14. Ideas and effects which always accompany each other, are supposed to be derived from the fame cause, e. g. If a body is interpofed between our two hands they cannot come together, this is an effect not a fimple idea probably produced by the body interpofed between the hands; if the fenfation produced in the mind by feeling be called folidity, folidity in one body will be quite different from solidity in another, and neither one of those can be proved to be the cause why the hands do not come together; but it may be faid, that what produces them likewife keeps the hands from coming together, the confequence is that they may both be concluded properties of the fame body, but no more deducible than other properties from each other.

15. Extenfion is a property of all bodies, the idea of it is acquired by the touch and all its measures as inches, feet, yards, miles, &c. derived from thence.

16. From the fame caufe, as before faid, is

derived

derived a correspondent idea by the fight which always accompanies the former; when different ideas are derived from the fame caufe, we afsociate them together in our mind as we find them from experience, e. g. We have found bodies greater to the touch when the picture on the retina is greater, if the diftance from the eye be the fame; we therefore judge of the greatness of one from the other: from the angle which the objects fubtend at the eye, the light and shades, distinctness and greatness, &c. of a known object, do we judge of its tangible distance, fize and fhape according to past experience; and the fame principles which we have deduced by experience from known objects do we apply to unknown: in general from an idea of one sense, we can feldom judge with much accuracy and precision concerning an idea excited from the fame cause through a different sense; but in the cafe of our ideas of extenfion from fight and touch there is an exception, by making ufe of both together: we are able to extend our measures by touch alone to a small distance, but by taking two different angles by inftruments accommodated to the fight, at a proper and known tangible distance from each other; and the fame for more angles and distances; and by fuppofing the motion of the earth and heavenly bodies to be conformable to past observations

and

and experience we can extend this measure to distances almost as far as imagination can reach, and prove that the eye extends its view to inacceffible diftances, to millions, billions, and trillions, and a space equal to fextillions or nonillions of miles; but to how much further the naked eye, and much more affifted by telescopic inftruments, views, can never be investigated: stupendous, immenfe, perceptible space! through the whole of which are interfperfed indefinite fystems of bodies equal to our own; how small and contemptible is the world which we inhabit to our fyftem of Sun, Planets, Comets and Satellites? how little the space that a fingle perfon inhabits to the world? infinite creation! yet every part connected, communicating, affording light, and probably attracting and giving vigour, &c. to each other; therefore only one infinite machine, proving by the communication of its parts, the omnipotency and the unity of its fupreme Architect; power infinitely fuperior to human comprehenfion.

17. But great, infinite as the creation is in its extent, it displays in its smallest parts, in man, in other terreftrial animals equal power in miniature; the number of veffels carrying blood and various other juices, of glands fecreting them, of nerves affording life and action to every part of the fibres which confti

tute the muscles, veffels and other parts of the body is never to be investigated, I may venture to fay, that they are innumerable; the whole world filled with animals innumerable, most of them imperceptible by us, as is probably all the other creation.

18. Such is the infinite power of the Creator, nor is his wisdom and goodness lefs difplayed, were we endued with faculties able to comprehend them; i. e. Were the understanding equal in force to the fenfe; infinite wifdom and goodness always accompany each other. Wisdom confifts in seeing what is neceffary for the well being of any animal, goodness in giving the means affording it; from the goodness therefore given we deduce the wisdom. At a great distance worlds to our view are crowded into points, and only can barely be feen, not the living animals or various other parts contained in them, and confequently not their contributing to the well being of each other. Our fenfes are not calculated to afford us much infight into things at a great distance which could be of no benefit to us, our understanding is limited even to the knowledge of a very fmall part of the wifdom difplayed in the things with which we are furrounded and converfant. Our minds are better formed to fee the ufes, than to examine the mechanism

from

from which they are produced; and we feel and are more convinced of the utility of any thing by being deprived, than by constantly enjoying the benefit of it: e. g. Let man be deprived of food, he foon becomes well convinced of the utility of it for the support of life; let him be deprived of a leg or an arm, and he foon perceives how useful it is to his well being; let him be deprived of his heart, his lungs, &c. and it foon appears how neceffary they are to his continuance in life: cut off the extenfors and flexors and mufcles of the legs, arms, &c. and it will immediately appear how neceffary and useful they are to the extending, bending and moving of their respective parts; cut off the blood veffels belonging to any mufcle, and the muscle immediately becomes inactive; cut off the nerve of any part, and it lofes its life and motion; in the fame manner we may defcend to the inferior veffels and parts, and shall find them all neceffary to the support and well being of the fuperior; and this may be carried perhaps in infinitum, could our fenfes afford us information fo far downwards.

The mechanism therefore infinitely furpaffes our understanding; which extends not fo far as from the parts in the leaft to investigate their uses, but it deduces, their uses as before feen from a deprivation of the parts.

B 2

19. We