[40] Lyell’s Principles of Geology, vol. i. Fourrier, Mém. de l’Acad. des Sciences, tom. vii. p. 592. “L’établissement et le progrès des sociétés humaines, l’action des forces naturelles, peuvent changer notablement, et dans de vastes contrées, l’état de la surface du sol, la distribution des eaux, et les grands mouvemens de l’air. De tels effets sont propres à faire varier, dans le cours de plusieurs siècles, le dégré de la chaleur moyenne; car les expressions analytiques comprennent des coefficiens qui se rapportent à l’état superficiel, et qui influent beaucoup sur la valeur de la température.” In this enumeration, by M. Fourrier, of causes which may vary the general relation of the surface of extensive continents to heat, it is but justice to Mr. Lyell to observe, that the gradual shifting of the _places_ of the continents themselves on the surface of the globe, by the abrading action of the sea on the one hand, and the elevating agency of subterranean forces on the other, does not expressly occur and cannot be fairly included in the general sense of the passage, which confines itself to the consideration of such changes as may take place on the existing surface of the land. [41] The reader will find this subject further developed in a paper lately communicated to the Geological Society. [42] Phil. Trans. 1824. [43] Wells on Dew. [44] Principia, book iii. prop. 6. [45] A very curious instance of the pursuit of a law completely empirical into an extreme case is to be found in Newton’s rule for the dilatation of his coloured rings seen between glasses at great obliquities. Optics, book ii. part i. obs. 7. [46] See Phil. Trans. 1819. [47] “When we are told that Saturn moves in his orbit more than 22,000 miles an hour, we fancy the motion to be swift; but when we find that he is more than three hours moving his own diameter, we must then think it, as it really is, slow.” Thirty Letters on various Subjects, by William Jackson, 1795. [48] Thomson’s First Principles of Chemistry. [49] There seems no doubt, however, that an achromatic telescope had been constructed by a private amateur, a Mr. Hall, some time before either Euler or Dollond ever thought of it. [50] We allude to the recently invented achromatic combinations of Messrs. Barlow and Rogers, and the dense glasses of which Mr. Faraday has recently explained the manufacture in a memoir full of the most beautiful examples of delicate and successful chemical manipulation, and which promise to give rise to a new era in optical practice, by which the next generation at least may benefit. See Phil. Trans. 1830. [51] Alphonso of Castile, 1252. [52] Jackson, Letters on Various Subjects, &c. [53] Thomson’s First Principles of Chemistry, Introduction. [54] The progress of astronomical discovery has since shown that this law cannot be relied on (1851). [55] Novum Organum, part ii. table 2. (24), (30), &c. on the form or nature of heat.