About a month after writing the letter of which the above forms a part, Faraday again wrote to his friend Abbott, giving him an account of some experiments, in which he had been assisting Sir Humphry Davy, on "the detonating compound of chlorine and azote, and of four different and strong explosions of the substance, explosions from which neither he nor Davy had altogether escaped unhurt." "Of these," he says, "the most terrible was when I was holding between my thumb and finger a small tube containing 7-1/2 grains of the compound. My face was within twelve inches of the tube; but I fortunately had on a glass mask. It exploded by the slight heat of a small piece of cement that touched the glass above half-an-inch from the substance, and on the outside. The explosion was so rapid as to blow my hand open, bear off a part of one nail, and has made my fingers so sore that I cannot yet use them easily. The pieces of the tube were projected with such force as to cut the glass face of the mask I had on." In the other three experiments also they each of them got more or less cut about by the explosion of the "terrible compound," as Faraday calls it, Davy, indeed, in the last one, getting somewhat seriously cut. He writes thus frequently to Abbott during the summer of 1813, giving him in the later letters some well thought-out ideas on lectures and lecturing, which we shall have occasion to glance at when we are considering Faraday himself in the capacity of a lecturer,--one of the most popular and yet truly scientific lecturers of any time. In this year, his twenty-first, Faraday joined the City Philosophical Society, which had been founded about five years earlier by Mr. Tatum, at whose house the meetings were held. The Society consisted of some thirty or forty individuals, "perhaps all in the humble or moderate rank of life;" and certainly all of them anxious to improve themselves and add to their knowledge of scientific subjects. Once a week the members gathered together for mutual instruction; each member opening the discussion in his turn by reading a paper of a literary or philosophical nature, any member failing to do so at his proper time being fined half-a-guinea. In addition, the members had what they modestly called a "class book," but probably very like what we should now call a manuscript magazine; in this each member wrote essays, and the work was passed round from one to another.