During these years, from 1825 to 1829, which had been thus occupied in an apparently fruitless quest, he had been far from idle. He had gone on contributing chemical papers to the _Philosophical Transactions_ and to the _Quarterly Journal_. These dealt with sulpho-naphthalic acid, with the limits of vaporisation, with caoutchouc, bisulphide of copper, the fluidity of sulphur and phosphorus, the diffusion of gases, and the relation of water to hot polished surfaces. He had also originated at the Royal Institution the Friday evening discourses (see p. 33), the first of which he held in 1826. For some years he himself delivered no inconsiderable portion of these discourses every session. In 1826 he gave six, in 1827 three, in 1828 five, in 1829 six, and these in addition to his regular afternoon courses of six or eight lectures on some connected subject. He had also, in 1826, begun the Christmas lectures adapted to a juvenile audience, and had in 1827 given a course of twelve lectures at the London Institution in Finsbury Circus. In addition to these labours he had, in 1827, brought out the first edition of his book on “Chemical Manipulation.” In 1829 he began his lectures at the Royal Military Academy at Woolwich, which continued till 1849. The year 1830 may be regarded as the close of the first period of Faraday’s researches, during which time, though much of his labour had been of a preparatory and even desultory kind, it had been a training for the higher work to come. He had made three notable discoveries in chemistry, the new substances benzol and butylene, and the solubility of naphthalene in sulphuric acid forming the first of a new class of bodies, the sulpho-acids. He had also made an important discovery in physics, that of the electromagnetic rotations. He had already published sixty original papers, besides many notes of lesser importance, nine of these papers being memoirs in the _Philosophical Transactions_. He had already begun to receive from learned societies, academies, and universities the recognition of his scientific attainments, and he had established firmly both his own reputation as a lecturer, and the reputation of the Royal Institution, which was the scene of his lectures. CHAPTER IV. SCIENTIFIC RESEARCHES: SECOND PERIOD.