Besides, considering the attention which, I am informed, is now given to this subject by philosophers in all parts of Europe, and the rapid progress that has already been made, and may be expected to be made in this branch of knowledge, all unnecessary delays in the publication of experiments relating to it are peculiarly unjustifiable. When, for the sake of a little more reputation, men can keep brooding over a new fact, in the discovery of which they might, possibly, have very little real merit, till they think they can astonish the world with a system as complete as it is new, and give mankind a prodigious idea of their judgment and penetration; they are justly punished for their ingratitude to the fountain of all knowledge, and for their want of a genuine love of science and of mankind, in finding their boasted discoveries anticipated, and the field of honest fame pre-occupied, by men, who, from a natural ardour of mind, engage in philosophical pursuits, and with an ingenuous simplicity immediately communicate to others whatever occurs to them in their inquiries. As to myself, I find it absolutely impossible to produce a work on this subject that shall be any thing like _complete_. My first publication I acknowledged to be very imperfect, and the present, I am as ready to acknowledge, is still more so. But, paradoxical as it may seem, this will ever be the case in the progress of natural science, so long as the works of God are, like himself, infinite and inexhaustible. In completing one discovery we never fail to get an imperfect knowledge of others, of which we could have no idea before; so that we cannot solve one doubt without creating several new ones. Travelling on this ground resembles Pope's description of travelling among the Alps, with this difference, that here there is not only _succession_, but an _increase_ of new objects and new difficulties. So pleas'd at first the tow'ring Alps we try, Mount o'er the vales, and seem to tread the sky. Th' eternal snows appear already past, And the first clouds and mountains seem the last, But those attain'd, we tremble to survey The growing labours of the lengthen'd way. Th' increasing prospect tires our wand'ring eyes, Hills peep o'er hills, and Alps on Alps arise. ESSAY ON CRITICISM. Newton, as he had very little knowledge of _air_, so he had few doubts concerning it. Had Dr. Hales, after his various and valuable investigations, given a list of all his _desiderata_, I am confident that he would not have thought of one in ten that had occurred to me at the time of my last publication; and my doubts, queries, and hints for new experiments are very considerably increased, after a series of investigations, which have thrown great light upon many things of which I was not able to give any explanation before.