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the whole system of the universe is constructed and supported.

Emma. But can philosophy be comprehended by children so young as we are? I thought that it had been the business of men, and of old men too.

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

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Charles. 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 refer1

ences to figures by means of large letters and small, the use of which I did not comprehend.

Father. It is frequently a dangerous prace tice for young minds to dip into subjects lat before they are prepared, by some previous sh

knowledge, to enter upon them; since it

may create a distaste for the most interest. ring topics. Thus those books which you ko

now read with so much pleasure would not che have afforded you the smallest entertain.

years ago,


you must have spelt out almost every word in each page. red The same sort of disgust will naturally be felt an by persons who attempt to read works of und science before the leading terms are explain

ed and understood. The word angle is con

tinually recurring in subjects of this sort, do en you know what an angle is?

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


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Father. An angłe is made by the opening of two straight* lines. In this figure (Plate 1. Fig. 1.) there are two straight lines AB and CB 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 B 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.

Emma. Are not some angles called right angles ?

Father. Angles are either right, acute, or

* Straight lines, in works of science, are usually des nominated right lines,

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

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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 containg 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.

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