(6) When the Sun sets behind a cloud it is a sign that the next day will be cloudy or rainy.
(7) A misty dawn shows the coming of a fine day.
(8) A low dawn, that is when the Sun shines clear on rising, shows the coming of a fine day.
(9) A high dawn, that is when the Sun rises over a haze, or clouds, shows wind.
To Light a Fire with the Heat of the Sun.—A small magnifying glass, or burning glass, is simply a convex lens. It is a little piece of apparatus that every boy should always carry with him just as he does his pocket knife and compass. A lens 1½ inches in diameter and having a 4-inch focus may be bought for 25 or 30 cents.
A lens of this kind will be found very useful in many ways, for it will greatly magnify any object such as cloth, leaves, insects, finger-prints, in fact anything you may wish to see better than you could with your naked eye, though you cannot use a single lens for a spyglass. A magnifying glass will also frequently come in handy for lighting fires, by using the Sun’s rays when matches are scarce.
While a Boy Scout would disdain to use paper to kindle a fire, yet if a scrap of paper is at hand it will prove a good medium on which to direct the rays of the Sun with a burning glass. If you have no paper focus your glass on some punk or very dry leaves, as shown in [Fig. 37].
To focus the glass means to hold it away from the paper or leaves so that the rays of the Sun are brought to a point like the sharpened end of a lead pencil; when all the rays of sunlight, each of which carries a little heat, are brought to a point, they will make enough heat to light a piece of paper or a dry leaf.
Fig. 37.—Boy Focusing Burning Glass
on Leaves to Make Fire.