electricity, attraction of cohesion, spiritus rector, acrimony of the animal juices, &c. as terms of art, as unknown causes of known effects. But then they ought always to be defined, the definitions rigorously kept to, and all secondary ideas from prior associations excluded. Were this done in chemistry and medicine, it would produce a great reformation, and at once cut off many incumbrances, perplexities, and obscurities. The vis inertiæ of bodies, and the equivalent terms, were once terms of this kind, standing for the unknown cause of known phænomena. By degrees these phænomena were digested into order, the terms contributing thereto, and the three several kinds of them, classed respectively under the three laws of nature, which have been applied synthetically since, and given rise to the greatest mechanical discoveries. The same may be observed of gravity. And if the laws of magnetism, electricity, and the attraction of cohesion, could be ascertained in the same manner as the laws of the vis inertiæ and gravity, we should be enabled to predict and produce many effects of great importance to us.
It is of the highest use to us in practical matters, that the properties of bodies are so closely connected with each other. Thus the colour and specific gravity of a metal, the visible idea of a plant, also its taste or smell, give us a practical certainty in respect of all the other properties. This close connexion of the properties follows undoubtedly from the powers and mutual actions of the small parts; so that, if we could arrive at the knowledge of these last, we should immediately see not only the reason of all the properties of bodies, which are known at present, but be able to discover innumerable other relative ones. In the mean time we must endeavour to discover, digest, and register, the various properties of natural bodies, as they rise to view from suitable experiments; and thus prepare the way for those who shall hereafter decypher their internal constitution.
All the foregoing branches of knowledge ought to be considered as mere preparatories and preliminaries to the knowledge of religion, natural and revealed. They all, in their several orders and degrees, concur to establish the principal doctrines and duties of it; and these, when established, become the best means for attaining knowledge. The benevolence of the Deity, and the doctrine of final causes, are the best clew for guiding us through the labyrinths of natural phænomena, and particularly of those which relate to animals. The Scriptures are the only book which can give us any just idea of ancient times, of the original of mankind, their dispersion, &c. or of what will befall them in future generations. As to future things, predicted in the Scriptures, we can as yet collect nothing more than general intimations; but there is reason to believe, that succeeding generations
