HEAT CONSIDERED AS A MODE OF MOTION: BEING A COURSE OF TWELVE LECTURES DELIVERED AT THE ROYAL INSTITUTION OF GREAT BRITAIN IN THE SEASON BY JOHN TYNDALL, F.R.S., &c. PROFESSOR OF NATURAL PHILOSOPHY IN THE ROYAL INSTITUTION. WITH PLLUSTRATIONS. NEW YORK:· D. APPLETON AND COMPANY, 443 & 445 BROADWAY. 1866. PREFACE. GC354 тя 1866 IN the following Lectures I have endeavoured to bring the rudiments of a new philosophy within the reach of a person of ordinary intelligence and culture. The first seven Lectures of the course deal with thermometric heat; its generation and consumption in mechanical processes; the determination of the mechanical equivalent of heat; the conception of heat as molecular motion; the application of this conception to the solid, liquid, and gaseous forms of matter; to expansion and combustion; to specific and latent heat; and to calorific conduction. The remaining five Lectures treat of radiant heat; the interstellar medium, and the propagation of motion through this medium; the relations of radiant heat to ordinary matter in its several states of aggregation; terrestrial, lunar, and solar radiation; the constitution of the sun; the possible sources of his energy; the relation of this energy to terrestrial forces, and to vegetable and animal life. My aim has been to rise to the level of these questions from a basis so elementary, that a person possessing any imaginative faculty and power of concentration, might accompany me. 237351 Wherever additional remarks, or extracts, seemed likely to render the reader's knowledge of the subjects referred to in any Lecture more accurate or complete, I have introduced such extracts, or remarks, as an Appendix to the Lecture. For the use of the Plate at the end of the volume, I am indebted to the Council of the Royal Society; it was engraved to illustrate some of my own memoirs in the Philosophical Transactions.' For some of the Woodcuts I am also indebted to the same learned body. To the scientific public, the names of the builders of this new philosophy are already familiar. As experimental contributors, Rumford, Davy, Faraday, and Joule, stand prominently forward. As theoretic writers (placing them alphabetically), we have Clausius, Helmholtz, Kirchoff, Mayer, Rankine, Thomson; and in the memoirs of these eminent men the student who desires it, must seek a deeper acquaintance with the subject. MM. Regnault and Sèguin also stand in honourable relationship to the Dynamical Theory of Heat, and M. Verdet has recently published two lectures on it, marked by the learning for which he is conspicuous. To the English reader it is superfluous to mention the well-known and highly-prized work of Mr. Grove. I have called the philosophy of Heat a new philosophy, without, however, restricting the term to the subject of Heat. The fact is, it cannot be so restricted; for the connection of this agent with the general energies of the universe is such, that if we master it perfectly, we master all. Even now we can discern, though but darkly, the greatness of the issues which connect themselves with the progress we have made-issues which were probably beyond the contemplation of PREFACE. those, by whose industry and genius the foundations of our present knowledge were laid. In a Lecture on the 'Influence of the History of Science on Intellectual Education,' delivered at the Royal Institution, Dr. Whewell has shown that every advance in intellectual education has been the effect of some considerable scientific discovery, or group of discoveries.' If the association here indicated be invariable, then, assuredly, the views of the connection and interaction of natural forces-organic as well as inorganic-vital as well as physical-which have grown, and which are to grow, out of the investigation of the laws and relations of Heat, will profoundly affect the intellectual discipline of the coming age. In the study of Nature two elements come into play, which belong respectively to the world of sense and to the world of thought. We observe a fact and seek to refer it to its laws,-we apprehend the law, and seek to make it good in fact. The one is Theory, the other is Experiment; which, when applied to the ordinary purposes of life, becomes Practical Science. Nothing could illustrate more forcibly the wholesome interaction of these two elements, than the history of our present subject. If the steam-engine had not been invented, we should assuredly stand below the theoretic level which we now occupy. The achievements of Heat through the steam-engine have forced, with augmented emphasis, the question upon thinking minds— 'What is this agent, by means of which we can supersede the force of winds and rivers-of horses and of men? Heat can produce mechanical force, and mechanical force can produce Heat; some common quality must therefore unite this agent and the ordinary forms |