‘Had Mr. Berthollet obtained oxygen from chlorine there would have been no error in his theory, but by not attending to the minute circumstances of his experiment, by not ascertaining that the water present acted no part and was not decomposed, he fell into an error, and of course all the conclusions he drew were false and erroneous. Nothing should be allowed but what can be proved by experiment, and nothing should be taken for granted upon analogy or supposition.’
Faraday concludes this lecture thus: ‘Mr. Davy now proceeded to comment and make observations on the former theory of chlorine gas. Here I was unable to follow him. The plan which I pursue in taking of notes is convenient and sufficient with respect to the theoretical and also the practical part of the lecture, but for the embellishments and ornaments of it it will not answer. Mr. Davy’s language at those times is so superior (and indeed throughout the whole course of the lecture) that then I am infinitely below him and am incapable of following him even in an humble style. Therefore I shall not attempt it; it will be sufficient to give a kind of contents of it.
‘He said that hypotheses should not be considered as facts and built upon accordingly. Nevertheless, if cautiously pursued, they might lead to mature fruit. That nothing should be taken for granted unless proved. By considering oxygen as contained in chlorine the whole chemical world had been wrapped in error respecting that body for more than one-third of a century.
‘He noticed that all the truly great scientific men were possessed of great humility and diffidence of their own opinions and powers. He spoke of Scheele, the discoverer of chlorine; observed that he possessed a truly philosophical spirit, gave up his opinions when he supposed them to be erroneous, and without hesitation or reluctance adopted those of others which he considered more correct; admired his spirit and recommended it to all philosophers; compared it to corn, which looked but simple and insignificant in blossom and asked for little praise, yet was the support of man.’
In this lecture Faraday gives the details of twenty experiments.
On April 8 Professor Davy lectured on Simple Inflammable Bodies. ‘Their number, excepting the metals, is six, which unite with oxygen and chlorine, the subjects of the two last lectures.’ He showed a jet of oxygen burning in hydrogen, and said, ‘In the burning of tallow, wax, oil, and wood it is the hydrogen of their bodies that causes the flame; though in most cases it is also combined with carbon, yet it is the hydrogen that produces the flame....
‘I have here a bladder filled with nitrous oxide gas; I will breathe it once or twice, but not so far as to incapacitate me from continuing the lecture. It produces a very pleasing sensation (far superior to the most exquisite liquors, such as champagne), and I have no doubt that if I were to continue it a few minutes longer I should make a very interesting exhibition to the company; but I would rather be excused....
‘If we suppose that the diamond is pure carbon, and is therefore the same as charcoal, we have a very strong presumptive reason to suppose that all matter is alike in all substances. If substances so opposite and so different as charcoal and diamond are in reality the same kind of matter, then the difference in other bodies is no proof that they also are not of the same kind of matter; and this would lead us to suppose that there is but one matter in nature, and that the difference in different bodies is owing to variety in the distance of the particles, to shape, and to size....
‘In conclusion several of these six simple combustibles I suspect to be compounds, and perhaps their nature may shortly be discovered....
‘What gives a strong colour to the idea of the compound nature of nitrogen is the quantity of it that can be obtained from animal bodies, whereas they imbibe none, they combine with none.