XLI. The evidence of our senses alone, then, is not sufficient to enable us to derive just conclusions from experiments; for caution, reflection, judgement, and reason, are always necessary; and sometimes in so great a degree, that all the exertion of human talents and ingenuity, is not equal to an adequate examination of the phenomena. Sir Isaac Newton, an Englishman, who was a genius of the first rate, and a member of the Royal Society of London, in the beginning of the present century, published various tracts upon optics, in which, he displayed a great novelty to the philosophers and mathematicians; that is, that all colours exist and are contained, actually and formally, in the rays of light; which are constituted of heterogeneous particles, of unequal refrangibility. He proved this singular opinion, with many experiments of exquisite invention, contrived and considered, with no less exquisite delicacy, and in fact, made more than a few converts to his opinion in many parts, but more especially among the English mathematicians; and a Mr. Gauger who was one of these, enforced the Newtonian doctrine, with a great number of additional experiments; but in a short time, one Senor Rizetti, wrote against this new system, and stated many experiments in favour of the old opinion, and even pretended, that those which had been quoted by Gauger, militated against the Newtonian sentiment. Gauger replied to this, and paid Rizetti in his own coin; that is, he not only defended the consequences which he deduced from his own experiments, but turned those derived from the experiments of Rizetti against the doctrine of the Italian. It is certain that experience, as applied to many objects, opens a most extensive and fertile field for exercising the ingenuity of man, and that nature, even to him who seeks to know her in that way, is in various instances impenetrable and inaccessible. XLII. But we should acknowledge that in general, the difficulties are not so invincible, as not to be surmounted by reason and industry, and that the deceptions which sometimes result from experiments, proceed either from the want of proper diligence and attention in making them, or from the want of adequate ingenuity, to judge of, and decide upon them.