fubftance,) it is altogether fuperfluous to expatiate upon the use. No man disputes it. The observations, therefore, which I fhall offer, refpect that little which we seem to know of its conftitution.

Light paffes from the fun to the earth in eleven minutes; a distance, which it would take a cannon ball twenty-five years, in going over. Nothing more need be said to fhew the velocity of light. Urged by fuch a velocity, with what force muft its particles drive against, I will not say the eye, the tenderest of animal substances, but every substance, animate or inanimate, which ftands in its way? It might feem to be a force fufficient to shatter to atoms the hardest bodies.

How then is this effect, the confequence of fuch prodigious velocity, guarded againft? By a proportionable minuteness of the particles of which light is compofed. It is impoffible for the human mind to imagine to itself any thing fo small as a particle of light. But this extreme exility, though difficult to conceive, it is easy to prove. A drop of tallow, expended in the wick of a farthing candle, fhall fhed forth rays fufficient to fill a hemifphere of a mile diameter; and to fill it fo full of these rays,

rays, that an aperture not larger than the pupil of an eye, wherever it be placed within the hemisphere, shall be sure to receive fome of them. What floods of light are continually poured from the fun we cannot estimate; but the immensity of the sphere which is filled with its particles, even if it reached no further than the orbit of the earth, we can in fome fort compute: and we have reafon to believe, that, throughout this whole region, the particles of light lie, in latitude at least, near to one another. The fpiffitude of the fun's rays at the earth is fuch, that the number which falls upon a burning glafs of an inch diameter, is fufficient, when concentrated, to fet wood on fire.

The tenuity and the velocity of particles of light, as afcertained by feparate obfervations, may be faid to be proportioned to each other: both furpaffing our utmost stretch of comprehenfion; but proportioned. And it is this proportion alone, which converts a tremendous element into a welcome visitor.

It has been observed to me by a learned friend, as having often ftruck his mind, that, if light had been made by a common artist, it would have been of one uniform colour:

whereas, by its present compofition, we have that variety of colours, which is of fuch infinite use to us for the distinguishing of objects; which adds fo much to the beauty of the earth, and augments the stock of our innocent pleafures.

With which may be joined another reflection, viz. that, confidering light as compounded of rays of feven different colours, (of which there can be no doubt, because it can be refolved into these rays by fimply paffing it through a prifm,) the constituent parts must be well mixed and blended together, to produce a fluid, fo clear and colourlefs, as a beam of light is, when received from the fun.

CHAP

CHAPTER XXII.

ASTRONOMY *.

My opinion of Aftronomy has always been,

that it is not the best medium through which to prove the agency of an intelligent Creator; but that, this being proved, it fhews, beyond all other sciences, the magnificence of his operations. The mind which is once convinced, it raises to fublimer views of the Deity, than any other fubject affords; but is not fo well adapted, as fome other subjects are, to the purpose of argument. We are deftitute of the means of examining the conftitution of the heavenly bodies. The very fimplicity of their appearance is against them. We fee nothing, but bright points, luminous circles, or the phases of spheres reflecting the light which

* For the articles in this chapter marked with an asterisk, I am indebted to fome obliging communications, received (through the hands of the Lord Bishop of Elphin) from the Rev. J. Brinkley, M. A. Andrew's Profeffor of Aftronomy in the University of Dublin.

falls

falls upon them. Now we deduce defign from relation, aptitude, and correfpondence of parts. Some degree therefore of complexity is neceffary to render a subject fit for this fpecies of argument. But the heavenly bodies do not, except perhaps in the inftance of Saturn's ring, present themselves to our observation as compounded of parts at all. This, which may be a perfection in them, is a disadvantage to us, as enquirers after their nature. They do not come within our mechanics.

And what we fay of their forms, is true of their motions. Their motions are carried on without

any sensible intermediate apparatus: whereby we are cut off from one principal ground of argumentation and analogy. We have nothing wherewith to compare them; no invention, no discovery, no operation or refource of art, which, in this respect, resembles them. Even those things which are made to imitate and reprefent them, fuch as orreries, planetaria, cœleftial globes, &c. bear no affinity to them, in the cause and principle by which their motions are actuated. I can affign for this difference a reason of utility, viz. a reason why, though the action of terreftrial bodies upon each other be, in almost all cases, through

the