An account of four of these lectures ‘was taken off from notes by Mr. Faraday.’ The subjects were Radiant Matter, Chlorine, Simple Inflammables, and Metals. After the report of each lecture he gave the experiments as a sequel, illustrated with drawings; the whole made a small quarto of 386 pages, with an index of twenty-five pages. The volume was bound by Mr. Faraday, and was sent to Davy as an evidence of Faraday’s ‘knowledge, diligence, and order,’ when he asked for an engagement at the Royal Institution. Davy gave the lecture on Radiant Matter on February 29. He said, ‘With respect to radiant or ethereal substances all our knowledge of it is obtained from the effect it produces on us and terrestrial bodies when in motion. ‘In our consideration of this subject it will be essentially necessary that we distinguish between knowledge and speculation. These terms in their meaning are palpably different, but yet have been intermixed and _combined_ together in a very singular manner. The French chemists in particular speak of the materiality of heat, and of the nature of the compounds it forms, as confidently and as fluently as if they had undeniably proved it to be a body. They have blended their knowledge with speculation, and formed a theory that is very possibly untrue. The most eminent phenomena of radiation are to be observed in light.’ And then he passed on to the laws of light and dwelt on Herschel’s discovery that the heating power of red rays was to the green as fifty-five to sixteen, and that he had himself found the thermometer rose still higher beyond the red, and that heating rays are less refrangible than light rays; then he showed a wire heated by the voltaic battery in air and in vacuo, and said that he had proved ‘that the radiating power is three times as strong in an exhausted receiver as in the open air,’ and, ‘fully proves that radiation is not caused by undulations in the atmosphere. It is strongest when no atmosphere is present.’ He ends his account of the effects of radiant heat thus: ‘Were it not for this terrestrial radiation of earthly bodies, the heat would accumulate from the rays of the sun until at last the whole world would be uninhabitable. ‘But, besides the effects produced by the two species of radiant matter--radiant light and radiant heat--there are other effects--chemical effects--that take place caused by the action of some radiant matter that comes to us from the sun, perhaps a single substance that, independent of light and heat, causes effects by its own power.’ And then he showed an experiment of chlorine and hydrogen exposed to light. He says, ‘There is a very singular analogy that exists between the rays at the violet end of the spectrum, hydrogen gas, and the negative pole of the voltaic battery; and opposed to it stands the analogy of the rays at the red end of the spectrum to positive electricity; they produce opposite effects to the first-mentioned arrangement, but act similar to each other.