It is admitted on all hands that the demonstration is complete which shows the existence of intelligence and design in the universe. The structure of the eye and ear in exact confirmity to the laws of optics and acoustics, shows as clearly as any experiment can show anything, that the source, cause or origin is common both to the properties of light and the formation of the lenses and retina in the eye--both to the properties of sound and the tympanum, malleus, incus and stapes of the ear. No doubt whatever can exist upon the subject, any more than, if we saw a particular order issued to a body of men to perform certain uncommon evolutions, and afterwards saw the same body performing those same evolutions, we could doubt their having received the order. A designing and intelligent and skillful author of these admirably adapted works is equally a clear inference from the same facts. We can no more doubt it than we can question, when we see a mill grinding corn into flour, that the machinery was made by some one who designed by means of it to prepare the materials of bread. The same conclusions are drawn in a vast variety of other instances, both with respect to the parts of human and other bodies, and with respect to most of the other arrangements of nature. Similar conclusions are also drawn from our consciousness, and the knowledge which it gives us of the structure of the mind.[3] Thus we find that attention quickens memory and enables us to recollect; and that habit renders all exertions and all acquisitions easy, beside having the effect of alleviating pain.