47. (Pg. 89) What was formerly supposed respecting the motion of all the heavenly bodies? 48. (Pg. 89) What do we mean by the Copernican system, and what is said respecting Copernicus and Newton? 49. (Pg. 90) What circumstance is said to have given rise to the speculations of Newton, on the subject of gravitation? CONVERSATION VIII. ON THE EARTH. OF THE TERRESTRIAL GLOBE. OF THE FIGURE OF THE EARTH. OF THE PENDULUM. OF THE VARIATION OF THE SEASONS, AND OF THE LENGTH OF DAYS AND NIGHTS. OF THE CAUSES OF THE HEAT OF SUMMER. OF SOLAR, SIDERIAL, AND EQUAL OR MEAN TIME. MRS. B. As the earth is the planet in which we are the most particularly interested, it is my intention this morning, to explain to you the effects resulting from its annual, and diurnal motions; but for this purpose, it will be necessary to make you acquainted with the terrestrial globe: you have not either of you, I conclude, learnt the use of the globes? _Caroline._ No; I once indeed, learnt by heart, the names of the lines marked on the globe, but as I was informed they were only imaginary divisions, they did not appear to me worthy of much attention, and were soon forgotten. _Mrs. B._ You supposed, then, that astronomers had been at the trouble of inventing a number of lines, to little purpose. It will be impossible for me to explain to you the particular effects of the earth's motion, without your having acquired a knowledge of these lines: in plate 8. fig. 2. you will find them all delineated: and you must learn them perfectly, if you wish to make any proficiency in astronomy. _Caroline._ I was taught them at so early an age, that I could not understand their meaning; and I have often heard you say, that the only use of words, was to convey ideas. _Mrs. B._ A knowledge of these lines, would have conveyed some idea of the manner in which they were designed to divide the globe into parts; although the use of these divisions, might at that time, have been too difficult for you to understand. Childhood is the season, when impressions on the memory are most strongly and most easily made: it is the period at which a large stock of terms should be treasured up, the precise application of which we may learn when the understanding is more developed. It is, I think, a very mistaken notion, that children should be taught such things only, as they can perfectly understand. Had you been early made acquainted with the terms which relate to figure and motion, how much it would have facilitated your progress in natural philosophy. I have been obliged to confine myself to the most common and familiar expressions, in explaining the laws of nature; although I am convinced that appropriate and scientific terms, might have conveyed more precise and accurate ideas, had you been prepared to understand them. _Emily._ You may depend upon our carefully learning the names of these lines, Mrs. B.; but before we commit them to memory, will you have the goodness to explain them to us?