Thus, the instantia crucis comes in real practice to be the experiment most frequently appealed to, and that from which the most valuable information is derived. • In executing the method here referred to, the application of much reasoning, and fre quently of much mathematical reasoning, is necessary, before any appeal to the experiment can be made, in order to deduce from each of the hypotheses an exact estimate of the con sequences to which it leads. Suppose, for instance, that the law by which the magnetic virtue decreases in its intensity, as we recede from its poles, were to be inquired into. It is obvious that the number of hypotheses is here indefinite ; and that we have hardly any choice but to begin with the simplest, or with that which is most analogous to the law -of other forces propagated from a centre. Whatever law we assume, we must enter into a good deal .of geometric. reasoning, before a conclusion can be obtained, capable of being brought to the test of experience. The force itself, like all other forces, is not directly perceived and its effects are not the result of its mere intensity, but of that intensity com bined with the figure and magnitude of the body on which its acts ; and, therefore, the calculus must be employed to express the measure of the effect, in terms of the intensity and the distance only. This being done, the hypothesis which gives results most nearly corresponding to the facts observed, when the magnet acts on the same body, at different distances, must be taken as the nearest approximation to the truth. We have here an in stance of the use of hypothesis in inductive investigation, and, indeed, of the only legiti mate use to which it can ever be applied.
It also appears that Bacon placed the ultimate object of philosophy too high, and too much out of the reach of man, even when his exertions are most skilfully conducted. He seems to have thought, that, by giving a proper direction to our researches, and carrying them on according to the inductive method, we should arrive at the knowledge of the essences of the powers and qualities residing in bodies ; that we should, for instance, be come acquainted with the essence of heat, of cold, of colour, of transparency. The fact, how ever, is, that, in as far as science has yet advanced, no one essence has been discovered, either as to matter in general, or as to any of its more extensive modifications. We are yet in doubt, whether heat is a peculiar motion of the minute parts of bodies, as Bacon himself conceived it to be ; or something emitted or radiated from their surfaces ; or lastly, the vibrations of an elastic medium, by which they are penetrated and surround ed. Yet whatever be the form or essence of heat, we have discovered a great number of its properties and its laws ; and have done so, by pursuing with more or less -accuracy the method of induction. We have also this consolation for the imperfection of our theoreti cal knowledge, that, in as much as art is concerned, or the possession of power over heat, we have perhaps all the advantages that could be obtained from a complete knowledge of its essence.
An equal degree of mystery hangs over the other properties and modifications of body ; light, electricity, magnetism, elasticity, gravity, are all in the same circumstances ; and the -- only advance that philosophy has made toward the discovery of the essences of these qua • lities or substances is, by exploding some theories, rather than by establishing any,—so true is Bacon's maxim, that the first steps in philosophy necessarily consist In negative propo sitions. Besides this, in all the above instances the laws of action have been ascertained ; the phenomena have been reduced to a few general facts, and in some cases, as in that of gravity, to one only ; and for ought that yet appears, this is the highest point which our science is destined to reach.
In consequence of supposing a greater perfection in knowledge than is ever likely to be attained, Bacon appears, in some respects, to have misapprehended the way in which it is ultimately to become applicable to art. He conceives that, if the form of any quality were known, we should be able, by inducing that form on any 'body, to communicate to it the said quality. It is not probable, however, that this would often lead to a more easy and simple process than that which art has already invented. In the case of colour, for example, though ignorant of its form, or of the construction of surface which enables bodies to reflect only light of a particular species, yet we know how to communicate that power from one body to another. Nor is it likely, though this structure were known with ever so great precision, that we should be able to impart it to bodies by any means so simple and easy, as by the common process of immersing them in a liquid of a given colour.
• In some instances, however, the theories of chemistry have led to improvements of art very conformable to the anticipations of the Novum Organum. A remarkable instance of this occurs in the process for bleaching, invented by Berthollet. It had been for some time known, that the combination of the chemical principle of oxygen with the colouring matter in bodies, destroyed, or discharged, the colour ; and that, in the common process of bleaching, it was chiefly by the union of the oxygen of the air with the colouring matter in the cloth that this effect was produced. The excellent chemist just named con ceived, therefore, that if the oxygen could be presented to the cloth in a dense state, and, at the same time, feebly combined with any other body, it might unite itself to the colour ing matter so readily, that the process of bleaching would by that means be greatly acce• lerated. His skill in chemistry suggested to him way in which this might easily be done, by immersing the cloth in a liquid containing much oxygen in a loose state, or one in which it was slightly combined with other substances, and the effect followed so exactly, that he was able to perform in a few hours what required weeks, and even months, accord ing to the common process. improvement, therefore, was a real gift from the sciences to the arts ; and came nearly, though not altogether, up to the ideas of Bacon. I suspect not altogether, because the manner in which oxygen destroys the colour of bodies, or alters • the structure of their surfaces, remains quite unknown.
It was natural, however, that Bacon, who studied these subjects theoretically, and saw nowhere any practical result in which he could confide, should listen to the inspirations of his own genius, and ascribe to philosophy a perfection which it may be destined never to attain. He knew, that from what' it had not yet done, he could conclude nothing against what it might hereafter accomplish. But after his method has been fol. lowed, as it has now been, with greater or less accuracy, for more than two hundred years, 'circumstances are greatly changed ; and the impediments, which,. during all that time, have not yielded in the least to any effort, are perhaps never likely to be removed. This may, however, be a rash inference ; Bacon, after all, may be in the right ; and we may be judging under the influence of the vulgar prejudice, which has convinced men, in every age, that they had nearly reached the farthest verge of human know ledge. This must be left for the decision of posterity; and we should rejoice to think, that judgment will hereafter be given against the opinion which. at this momentiappeare most probable.