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?
A. When a cloud, overcharged with electric fluid, approaches another which is under-charged, the fluid rushes from the former into the latter, till both have the same quantity.
Q. Is there any other cause of lightning, besides the one
