Father. Philosophy is a word which in its original sense signifies only a love or desire of wisdom; and you will not allow that you and your brother are too young to wish for knowledge.

Emma. So far from it, that the more knowledge I get the better I seem to like it; and the number of new ideas which, with a little of your assistance, I have obtained from the "Evenings at Home," and the great pleasure which I have received from the perusal of these volumes, will, I am sure, excite me to read them again and again.

Father. You will find very little in the introductory parts of natural and experimental philosophy, that requires much more of your attention than many parts of that work with which you have been so delighted.

Charies. But in some books of natural philosophy, which I have occasionally looked into, a number of new and uncommon words have perplexed me; I have also seen references to figures by means of large letters and small, the use of which I did not comprehend.

Father. It is frequently a dangerous practice for young minds to dip into subjects before they are prepared, by some previous knowledge, to enter upon them; since it may create a distaste for the most interesting topics. Thus those books which you now read with so much pleasure would not have afforded you the smallest

entertainment a few years ago, when you must have spelt out almost every word in each page. The same sort of disgust will naturally be felt by persons who attempt to read works of science before the leading terms are explained and understood. The word angle is continually recurring in subjects of this sort, do you know what an angle is?

Emma. I do not think I do; will you explain what it means?

Father. An angle is made by the opening of two straight lines. In this figure (Plate 1. Fig. 1.) there are two straight lines AB and Cв meeting at the point B, and the opening made by them is called an angle.

Charles. Whether that be small or great, is it still called an angle?

Father. It is; your drawing compasses may familiarize to your mind the idea of an angle ; the lines in this figure will aptly represent the legs of the compasses, and the point в the joint upon which they move or turn. Now you may open the legs to any distance you please, even so far that they shall form one straight line; in that position only they do not form an angle. In every other situation an angle is made by the opening of these legs, and the angle is said to be greater or less, as that opening is greater or less.

* Straight lines, in works of science, are usually denominated right lines.

Emma. Are not some angles called right angles ?

Father. Angles are either right, acute, or obtuse. When the line AB (Plate 1. Fig. 2.) meets another line pc, in such a manner as to make the angles ABD and ABC equal to one another, then those angles are called right angles. And the line AB is said to be perpendicular to DC. Hence to be perpendicular to, or to make right angles with a line, means one and the same thing.

Charles. Does it signify how you call the letters of an angle?

Father. It is usual to call every angle by three letters, and that at the angular point must be always the middle letter of the three. There are cases, however, where an angle may be denominated by a single letter, as in figures 1 and 3, the angle ABC may be called simply the angle B, for in these figures there is no danger of mistake, because there is but a single angle at the point B.

Charles. I understand this, for if in the second figure I were to describe the angle by the letter B only, you would not know whether I meant the angle ABC or ABD.

Father. That is the precise reason why it is necessary in most descriptions to make use of three letters. An acute angle (Fig. 1.) ABC is less than a right angle; and an obtuse angle (Fig. 3.) ABC is greater than a right angle.

Emma. You see the reason now, Charles, why letters are placed against or by the figures, which puzzled you before.

Charles. I do: they are intended to distinguish the separate parts of each, in order to render the description of them easier both to the author and the reader.

Emma. What is the difference between an angle and a triangle?

Father. An angle being made by the opening of two lines, and, as you know, that two straight lines cannot enclose a space, so a triangle ABC (Fig. 4.) is a space bounded by three straight lines. It takes its name from the property of containing three angles. There are various sorts of triangles, but it is not necessary to enter upon these particulars, as I do not wish to burden your memories with more technical terms than we have occasion for.

Charles. A triangle then is a space or figure containing three angles, and bounded by as many straight lines.

Father. Yes, that description will answer our present purpose.

VOL. I.B

CONVERSATION II.

Of Matter. Of the Divisibility of Matter.

Father. Do you understand what philosophers mean when they make use of the word matter? Emma. Are not all things which we see and feel composed of matter?

Father. Every thing which is the object of our senses is composed of matter differently modified or arranged. But in a philosophical sense matter is defined to be extended, solid, inactive, and moveable substance.

Charles. If by extension is meant length, breadth, and thickness, matter, undoubtedly, is an extended substance. Its solidity is also manifest by the resistance it makes to the touch.

Emma. And the other properties nobody will deny, for all material objects are, of themselves, without motion: and yet it may be readily conceived, that by the application of a proper force there is no body which cannot be moved. But I remember, papa, that you told us something strange about the divisibility of matter, which you said might be continued without end.

Father. I did, some time ago, mention this as a curious and interesting subject, and this is a very fit time for me to explain it.