A Text Book Of Physics

A TEXT-BOOK OF PHYSICS HEAT A TEXT-BOOK OF PHYSICS. 13 y J. II. POYNTING, So.., F. R. S. FOREIGN MKMHKU K THE ACVADEMIV DKI LINCEI, R nnfi Hov T So, YinoniA i T Ni KRMtT, LATE FALLOW OF TKFNITY COLLI-GF, C Mimu ui, MASON VKOKESSOH F PHYSICS IN Tilt UNIVKKSITY OK BIUMINUUAM AND SIR J. J. THOMSON, M. A., F. R. S. VIHK K THK IN TITI TK K FUANCK, FORT-IOV MT MBFH OF TIIL M, liON tK 1 1, DLUSMN, IIuN D J, PKIM TUW. N, lldN, I sc, VKTOKU, Ifos U I, ii io, HON Pu J, CRACOW K TlllNlTTi CohLEfiK, CAMUHJDGK, IVJ-ADTsiI PRO fs H OK E 1 HUMF, NTAL PlIYblCS IN TIIK IJNIVFR irV V I VMKIUH, PllOl-KssoK UF li IN TIIJ Jt L i HEAT. WITH 193 ILLUSTRATIONS, KIOHTH EDITION LONDON CHARLES GRIFFIN AND COMPANY, LIMITED, 42 DBURY LANE, W. 0. 2. 1925. Rights Reserved Pimted in Great Britain bv NF. ILL Co, LID, EDINBURGH. PREFACE TO FOURTH EDITION. WE desire to express our hearty thanks to readers of the earlier editions of this volume who havo kindly sent us lists of errata, These have been corrected, and a number of alterations and additions have been made. Reprinted for Eighth Edition, Xept. 1925. PREFACE. THIS volume on Heat is tho third of a series forming a Text-Book on Physics. Tho iirst two volumes dealt with the Properties of Matter and Sound, and the succeeding volumes will deal with Magnetism and Electricity, and Light. The Text-Book is intended chiefly for the use of students who lay most stress on the study of the experimental part of Physics, and who have not yet reached the stage at which the reading of advanced treatises on special subjects is desirable. To bring the subject within the compass thus prescribed, an account is given only of phenomena which are of special importance, or which appearto throw light on other branches of Physics, and the mathematical methods adopted are very elementary. The student who possesses a knowledge of advanced mathematical methods, and who knows how to use them, will, no doubt, be able to work out and remember most easily a theory which uses such methods. But at present a large number of earnest students of Physics are not so equipped, and the authors aim at giving an account of the subject which will be useful to students of this class. Even for the reader who is mathematically trained, there is some advan tage in the study of elementary methods, compensating for their cumbrous form. They bring before us more evidently the points at which various assumptions are made, and they render more prominent the conditions under which the theory holds good. J. H. P, CONTENTS. CHAPTER I. TEMPERATURE. PAQK8 Introductory Remarks Temperature Thermal Equilibrium Construction of Mercury - Glass Thermometers Fixed Points Centigrade, Fahrenheit, and Reaumur Scales Marking Fixed Points Calibration and Giaduation Precautions in use Limits of accuracy Range Scales of Temperature given by expansion arbitrary The Work Scale Air and Hydrogen Scales Platinum Resistance Thermometers Table of Temperatures Maximum and Minimum Thermometer Thermostats ...... 1-18 CHAPTER II. EXPANSION OF SOLIDS WITH RISE OF TEMPERATURE. Linear Expansion of Solids Ramsdens Method Modern Use of the Method Method of Lavoisier and Laplace-Results - Fizeaus Optical Method Applications of Linear Expansion Volume Expansion of Solids . . 1728 CHAPTER III. EXPANSION OF LIQUIDS. Volume Expansion of Liquids U-Tube Method applied to Mercury Dulong and 1 etit llegnault Expansion of other Liquids bySpecific Gravity Bottle By Dilatometer--Matthiessens Hydrostatic Method The Expan sion of Water Hopes Apparatus Apparatus of Joule and Playfair Results 29-40 CHAPTER IV. EXPANSION OF GASES. Expansion of Gases depends on Pressure Changes Volume Expansion at Constant Pressure Gay-Lussacs Method Regnaults Experiments Increase of Pressure with Constant Volume Gas Thermometry Kegiiaults Normal Air Thermometer Hydrogen Thermometer Bottomleys Air Thermometer Calleridars Compensated Air Thermometer . . . 41-62 vii viii CONTENTS. CHAPTER V...