XIII.--COMMUNICATION OF HEAT XIII.--Conduction XIV.--Absorption XV.--Reflection XVI.--Radiation (dew) XVII.--Convection (boiling) PART II.--AIR. XVIII.--AIR Rust Tarnish XIX.--CARBONIC ACID GAS Froth Effervescence Fermentation, &c. XX.--CARBURETTED HYDROGEN GAS Fire damp Safety lamp XXI.--PHOSPHURETTED HYDROGEN GAS Ignis fatuus Ghosts XXII.--WIND XXIII.--BAROMETER Ten special Rules XXIV.--SNOW. HAIL. RAIN XXV.--WATER XXVI.--ICE Frost Freezing mixtures XXVII.--LIGHT Reflection Telescopes Refraction Spectacles Rainbows Colour XXVIII.--SOUND Ear trumpets Echoes XXIX.--MISCELLANEOUS Attraction Anti-putrescents Sleep Dreams Glossary Index PART I. HEAT. INTRODUCTION. Q. _What is heat?_ A. The sensation of warmth. Q. _How is this sensation produced?_ A. When we touch a substance of higher temperature than ourselves, the warmer substance keeps parting with its heat, till both are of equal temperature. Q. _What is that "stream of heat" called, which flows thus, from one body, to another?_ A. CALO'RIC. _Caloric_, therefore, is the _matter of heat_, which passes from body to body; but HEAT is the _sensation, of warmth_, produced by the influx of Calo'ric. Q. _What are the four principal_ SOURCES _of heat_? A. 1.--The Sun. 2.--Electricity. 3.--Chemical Action: and 4.--Mechanical Action. Q. _What are the principal_ EFFECTS _of heat_? A. Expansion, Liquefaction, Vaporization, and Ignition. CHAPTER I. Q. _What is the_ PRINCIPAL _source of Heat_? A. The SUN. Q. _Why do_ BURNING GLASSES _set fire to substances submitted to their power_? A. The rays of the sun, collected by the Burning Glass, are all _bent to one point_, called the "focus;" thus the heat and light, (which should be diffused over the _whole_ glass,) being gathered together into one point, are very greatly increased. Q. _Why is there a_ DARK RIM _round this focus_? A. Because the rays of light, which should have fallen there, are _bent into the focus_, and the space around, (being deprived of these rays) is accordingly darkened. Q. _Are_ ALL _the rays bent into one point_? A. No, not quite all: and, therefore, the rim round the focus is only _slightly_ shadowed. CHAPTER II. Q. _What is the second chief source of heat?_ A. ELECTRICITY. Q. _What is_ LIGHTNING? A. Lightning is only an _Electric Spark, taken from the clouds_. Q. _What causes the discharge of an electric cloud?_