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The Barometer: Experiments

Instead of black, any other colour may be used. Verdigris makes a pleasant green; and by adding yellow ochre, or Prussian blue, you may approach the original tint of the leaf, and your impression will almost equal that of nature. Curious Experiments respecting Colours.

The following curious and useful remarks on the different degrees of heat imbibed from the sun's rays, &c. by cloths of different colours, were extracted from "Experiments and Observations," by that famous American philosopher and politician, Dr. B. Franklin. "First, let me mention an experiment you may easily make yourself. Walk but a quarter of an hour in your garden when the sun shines, with a part of your dress white, and a part black; then apply your hand to them alternately, and you will find a very great difference in their warmth. The black will be quite hot to the touch, the white still cool. "Another. Try to fire paper with a burning-glass. If it be white, you will not easily burn it; but if you bring the focus to a black spot, or upon letters written or printed, the paper will immediately be on fire under the letters. "Thus fullers and dyers find that black cloths, of equal thickness with white ones, and hung out equally wet, dry in the sun much sooner than the white, being more readily heated by the sun's rays. It is the same before a fire; the heat of which sooner penetrates black stockings than white ones, and is apt sooner to burn a man's shins. Also beer much sooner warms in a black mug set before the fire, than in a white one, or in a bright silver tankard. "My experiment was this: I took a number of little square pieces of broad cloth from a tailor's pattern-card, of various colours. There was black, deep blue, lighter blue, green, purple, red, yellow, white, and other colours, or shades of colours. I laid them all out upon the snow in a bright sunshiny morning. In a few hours, (I cannot now be exact as to the time,) the black being warmed most by the sun, was sunk so low as to be below the stroke of the sun's rays; the dark blue almost as low, the lighter blue not quite so low as the dark, the other colours less as they were lighter; and the quite white remained on the surface of the snow, not having entered it at all. "What signifies philosophy that does not apply to some use? May we not learn from hence, that black cloths are not so fit to wear in a hot sunny climate, or season, as white ones; because, in such clothes the body is more heated by the sun when we walk a proad, and are at the same time heated by the exercise, which double heat is apt to bring on putrid dangerous fevers?--that soldiers and seamen, who must march and la sour on the sun, should, in the East or West Indies, have a uniform of white? - that summer hats for men or women, should be white, as repelling that heat which gives head-achs to many, and to some the fatal stroke that the French call the coup de soliel?-that the ladies' summer hats, however, should be lined with black, as not reverberating on their faces those rays which are reflected upwards from the earth or water?-that the putting a white cap of paper or linen, within the crown of a black hat, as some do, will not keep out the heat, though it would if placed without?-that fruit-walls being blackened, may receive so much heat from the sun in the day-time, as to continue warm, in some degree, through the night, and thereby preserve the fruit from frosts, or forward its growth? - with sundry other particulars, of less er greater importance, that will occur from time to time to attentive minds?"