"Oh that men would praise the Lord for his goodness, and for his wonderful works to the children of men."-PSALM CVII.

52. Is animal heat really similar to the heat of the fire? Yes. All heat results from the presence of caloric, though the degrees of heat depend upon the various circumstances and proportions in which caloric appears. There is as much heat in the body of man as would, if it were compressed into a smaller space, cause a bar of iron, of considerable size, to become red-hot.

53. Why does exercise increase the heat of the body?

Because it accelerates the circulation of the blood for the purpose of sustaining the bodily effort required. And, as the blood circulates, more carbon is brought by the blood to the lungs, and the quicker breathing supplies an increased amount of oxygen to combine with the carbon, and therefore greater heat is evolved.

54. Why, if we quicken our breathing while sitting still, do we not increase the heat of our bodies?

Because, although we force air into the lungs, we do not increase the circulation of the blood. Therefore, the oxygen cannot combine with the carbon in any increased degree.

55. Why do poor and ill-fed people generally dislike fresh air?

Because the oxygen of the fresh air demands from their bodies a supply of fuel to the lungs which their scanty food cannot yield sufficiently. They therefore prefer ill-ventilated hovels to the purer air.

CHAPTER V.

56. Why is spring water frequently hard?

Because, by passing through the fissures of the earth, it comes in contact with mineral substances, and takes up in solution some of their particles. The existence of the minute particles of earthy matters among the atoms of water have a tendency to destroy its fluidity and softness.

57. Why is rain water soft?

Because, being distilled from the clouds, it is free from earthy matters, and its atoms possess their natural fluidity.

"The fear of the Lord is the beginning of knowledge: but fools despise wisdom and instruction."-PROVERBS I.

58. Why does the soap used in washing the hands float in flakes upon the top of hard water?

Because the lime, held in solution by the water, unites with the tallow, and forms an insoluble compound. The sulphate of lime neutralises the soda by combining with it, and therefore the cleansing power of the soap is impaired.

59. Why does carbonate of soda, or carbonate of potash, render hard water soft?

Because it combines with the lime held in solution in the water, and precipitates it. The soda, or potash, to be fully effective, should be dissolved in the water twenty-four hours previous to using it. The matters that harden the water would then sink to the bottom.

60. Why does a soap-bubble display prismatic colours? Because the rays of light that fall upon the bubble are refracted by it; and, as the thickness of the film changes, the degree of refraction varies, and thus the "play" of beautiful colours is produced.

The refraction of light, and the production of prismatic colours, surround us with most interesting phenomena. The laundress, whose active labours raise over the wash-tub a soapy froth, performs inadvertently one of the most delicate operations of chemistry-the chemistry of the imponderable agents-and the result of her manipulations manifests itself in the delicate colours that dance like a fairy light over the glassy films that follow the motion of her arms. The laughing child, throwing a bubble from the bowl of a tobacco-pipe into the air, performs the same experiment, and produces a result such as that which filled the philosophic Newton with unbounded joy. The foam of the sea-shore, the plumage of birds, the various films that float upon the surface of waters, the delicate tints of flowers, and the rich hues of luscious fruits, all combine to remind us, that every ray of light comes like an angelic artist sent from heaven, bearing upon his palette the most celestial tints, with which to beautify the earth, and show the illimitable glory of God.

61. Why can bubbles be best formed by the aid of soap? Because the soap, being diffused among the atoms of water, establishes between them a degree of tenacity, or cohesive power, which does not exist in water alone in sufficient force.

62. Why do soap-bubbles ascend?

Because, being filled with the warm air expired from the lungs,

'He hath made his wonderful works to be remembered: the Lord is precious and full of compassion."-PSALM CXL.

they are lighter than the colder external air. They are, therefore, pressed upwards by the denser air which surrounds them.

63. Why do soap-bubbles descend after a time?

Because the air within them becomes condensed by cooling; and as it contains a considerable proportion of carbonic acid gas, it is, together with the film of the bubble, heavier than the surrounding air.

64. Why does steam issue from the spout of a kettle ?

Because the heat of the fire passes into the water, and tends to separate the particles of which the water is composed. The heated portions of the fluid rise to the top, and when a certain degree of heat has entered the water, the cohesive force which held the particles together is so far overcome that some of the atoms fly away in the form of vapour.

65. What is caloric?

Caloric is an extremely subtle force, or property of matter, which resides in all substances, and is the source of what we term heat. Heat is caloric made apparent, or perceptible to the senses.

66. Why does the water in the kettle become hot? Because it absorbs caloric from the fire.

67. What becomes of the steam that flies away from the kettle?

It diffuses itself through the air of the room, until, meeting with a cold surface, it condenses, and returns to its original state of water. Or it passes into the outer air, and assists in the formation of clouds.

68. If a tumbler be held near the spout of the kettle, why will it become covered with moisture?

Because the cold glass condenses the steam, which forms minute drops of water that attach themselves to the glass.

69. Why, when cold glasses and decanters are introduced

"He causeth the vapours to ascend from the ends of the earth: he maketh lightnings for the rain: he bringeth the wind out of his treasuries."-PSALM XXXV.

into warm rooms, do they frequently become dulled by

moisture?

Because the vapour held in suspension in the air becomes cooled, and condenses upon them.

70. Why are southerly winds usually rainy?

Because they reach us from warm regions, and as they come across the sea, they imbibe a large amount of moisture; then, when they meet the colder air of our latitude, the moisture condenses, and falls as rain.

71. Why does the vapour of hot water rise upon the air? Because it is so attenuated by heat, that it is specifically lighter than the air, and therefore rises and floats upon it.

We frequently hear of the singing of a kettle; but do we fully comprehend the music of its song? Through how many centuries had that grim old bard chaunted his lay of progress, unheeded by the faithless groups that sat around, until the Marquis of Worcester, in the year 1663, published his account of "a fire water work," which he had discovered, and told how he had burst an old cannon by filling it with water, and "screwing up the broken end, as also the touch-hole;" and how, by "making a constant fire under it, within 24 hours it burst and made a great crack." Doubtless the kettle had tuned its song many times to the Marquis, until one day it sang with greater effect, and called attention to those portentous notes that it had so frequently uttered. Then the song of the kettle was one of complaint; now it is a hymn of triumph. Less than two centuries have passed since the discovery of the "fire water work" was announced, and now the kettle in various improved forms is working wonders in most parts of the world. The offspring of the old kettle contend with the mighty ocean and the tempestuous wind; they fly with bird-like speed over the face of the earth, and in practical effect expand time and shorten space; they plough, they dig, they weld, they weave, they clothe and feed the labourer, they enrich the capitalist, they protect the state. These glorious results were brought to pass through a Marquis listening to a tea kettle and interpreting its song! Thus it is shown that there is no voice in nature too humble to invite the ear; nor any human being so high but he may gather wisdom from nature's simplest lessons.

"For my days are consumed like smoke, and my bones are burned as an hearth."-PSALM CII.

CHAPTER VI.

72. Why do air and smoke ascend the chimney?

Because the air, as it sweeps through and over the fire, becomes rarefied, or expanded by heat; it is therefore specifically lighter than the surrounding air, which, pressing towards it, forces it up the chimney in a continuous stream.

73. Why does air, when there is a fire in a room, rush in through the crevices of the doors and windows?

Because, as the rarefied air ascends through the chimney, it disturbs the balance of density between the air in the room and the outer air. The dense and cold air, therefore, rushes in and displaces the rarefied and warm air.

74. Why do light and rarefied bodies ascend?

They ascend by the pressure of surrounding bodies acting upon them, and forcing them upwards.

It is a mistake to suppose that any bodies have of themselves a tendency to fly upward.

Even hydrogen gas, the lightest of all known bodies, has weight, and would fall to the earth, if not surrounded by the denser air.

75. Why are chimney pots set upon chimneys?

Because, by contracting the aperture of the chimneys, and allowing only space for the ascending air to escape, they prevent downward currents of cold air, which would descend through the chimney, and carry with them some part of the smoke and vapour of the fire.

76. Why do chimneys smoke when fires are first lighted? Because the heat is for a time insufficient to expand the air and move the cold column of air within the chimney.