Was it boiling, sir, eh? when you took it off the fire? That is the question, sir."

"Yes, sir, that was what I mean to say, sir," replied Thomas.

"Mean to say, sir! Then why didn't you say it, sir? Eh? There-no, don't put it on, sir; hold it still. Harry, reach me the thermometer," said Mr. Bagges, putting on his spectacles. "Let me see. The boiling point of water is two hundred and-what?"

"Two hundred and twelve, Fahrenheit," answered Master Wilkinson, "if commonly pure, and boiled in a metallic vessel, and under a pressure of the atmosphere amounting to fifteen pounds on every square inch of surface, or when the barometer stands at thirty inches."

"Gracious, what a memory that boy has!" exclaimed his uncle. "Well; now this water in the kettle-eh ?— why, this is not above one hundred and fifty degrees. There, sir, now set it on the fire, and don't bring me up cold water to make tea with again; or else," added Mr. Bagges, making a vague attempt at a joke, "or else—ch ?— you will get yourself into hot water."

Mr. Thomas was seized with a convulsion in the chest, which he checked by suddenly applying his open hand to his mouth, the effort distending his cheeks and causing his eyes to protrude in a very ridiculous manner, whilst Mr. Bagges disguised his enjoyment of the effects of his wit in a cough.

"Now let me see," said the old gentleman, musingly contemplating the vessel simmering on the fire; "how is. it, eh, Harry, you said the other day that a kettle boils ?"

"La!" interrupted Mrs. Wilkinson, who was of the party, "why, of course, by the heat of the coals, and by blowing the fire if it is not hot enough."

"Aha!" cried her brother, "that's not the way we account for things, Harry, my boy, eh? Now, convince your mother; explain the boiling of a kettle to her: come."

"A kettle boils," said Harry, "by means of the action of currents."

"What are you talking about? Boiling a plum-pudding in a tea-kettle!" exclaimed the mystified mamma.

"Currents of heated particles-of particles of hot water," Harry explained. "Suppose you put your fire on your kettle on the lid of it-instead of your kettle on your fire,-what then?"

"You would be a goose," said his mother.

"Exactly so or a gosling, rejoined her son; "the kettle would not boil. Water is a bad conductor of heat. Heat passes through the substance of water with very great difficulty. Therefore, it would have a hard matter to get from the top of a kettle of water to the bottom. Then how does it so easily get from the bottom to the top?"

"Ah!" sighed Mr. Bagges. "In my young days we should have said, because the heat rises, but that won't do What is all that about the-eh-what-law of ex

now.

what?-pansion-eh ?"

"The law of expansion of fluids and gases by heat. This makes the currents that I spoke of just now, mamma; and I should have spelt the word to explain to you that I didn't mean plums. You know what a draught is ?”

"I am sorry to say I do," Mr. Bagges declared with much seriousness, instinctively carrying his hand to the region of the human body from the Latin for which is derived the term Lumbago.

"Well," pursued Harry, "a draught is a current of air. Such currents are now passing up the chimney, and simply

owing to that trifling circumstance, we are able to sit here now without being stifled and poisoned."

"Goodness!" ejaculated Mrs. Wilkinson.

"To be sure. The fire, in burning, turns into gases, which are rank poison-carbonic acid, for one; sulphurous acid, for another. Hold your nose over a shovelful of hot cinders if you doubt the fact. The gases produced by the fire expand; they increase in bulk without getting heavier, so much so that they become lighter in proportion than the air, and then they rise, and this rising of hot air is what is meant by heat going upwards. The currents of hot air that go up the chimney in this way have currents of cold air rushing after them to supply their place. When you heat water, currents are formed just as when you heat gas or air. The heated portion of water rises, and some colder water comes down in its place; and these movements of the water keep going on till the whole bulk of it is equally hot throughout."

"Well, now," interrupted Mr. Bagges, "I dare say this is all very true, but how do you prove it ?"

"Prove that water is heated by the rising and falling of hot currents? Get a long, slender glass jar. Put a little water, colored with indigo, or any thing you like, into the bottom of it. Pour clear water upon the colored, gently, so as not to mix the two, and yet nearly to fill the jar. Float a little spirit of wine on the top of the water, and set fire to it. Let it blaze away as long as you like; the colored water will remain steady at the bottom of the jar. But hold the flame of a spirit-lamp under the jar, and the colored water will rise and mix with the clear, in a very little time longer than it would take you to say Harry Wilkinson."

"Ah! So the water gets colored throughout for the same reason that it gets heated throughout," Mr. Bagges observed, "and when it gets thoroughly hot-what then ?" "Then it boils. And what is boiling?"

"Bubbling," suggested the young philosopher's mamma. "Yes; but ginger-beer bubbles," said Harry, "but you wouldn't exactly call that boiling. Boiling is the escaping of steam. That causes the bubbling; so the bubbling of water over the fire is only the sign that the water boils. But what occasions the escape of the steam?"

"The heat, of course-the-what is the right word ?— the caloric," answered Mr. Bagges.

“True; but what heat? Why, the excess of heat over two hundred and twelve degrees-taking that as the average boiling point of water. You can heat water up to that point, and it remains water; but every degree of heat you cause to pass into it above that, turns a quantity of the water into steam; and flies off in the steam, unless the steam is hindered from escaping by extraordinary pressure. Blow the fire under that kettle as much as you will, and you will make the water boil faster, but you won't make it a bit hotter than two hundred and twelve degrees."

"Well, to be sure !" Mrs. Wilkinson exclaimed.

"If water," continued Harry, "could keep on getting hotter and hotter above the boiling point, why, we might have our potatoes charred in the pot, or our mutton boiled to a cinder. When water is confined in a strong vessel— and strong it must be to prevent a tremendous blow-upconfined, I say, so that no steam can escape, it may be heated almost red-hot; and there is a vessel made for heating water under pressure, called Papin's Digestor, which will digest almost any thing."

"What an enviable apparatus !" exclaimed Mr. Bagges.

"Well," resumed Harry; "so the boiling point of water depends on the degree of force which the air or what not is pressing on its surface with. The higher the spot on which you boil your water, the lower the point it boils at. Therefore, water boiling at the top of a mountain is not so hot as water boiling at the mountain's base. The boiling point of water on the summit of Mont Blanc, is as low as one hundred and eighty-four degrees. So, if water must be at two hundred and twelve degrees, to make good tea, don't choose too high a hill to build a temperance hall on. The heavier, also, the air is, from the quantity of moisture in it, the hotter water becomes before it boils. If the atmosphere were carbonic acid gas, water would get much hotter without boiling than it can under"

"Present arrangements," interposed Mr. Bagges.

"Consisting of a mixture of nitrogen and oxygen," continued Harry. "Water requires only a very low heat to make it boil in an exhausted receiver, out of which the air has been pumped, so as to leave none to press upon its surface. Owing to boiling depending upon pressure, you can actually make water boil by means of cold."

"What next?" sighed Mrs. Wilkinson.

"You can, indeed. Put a little boiling water in a salad-oil flask; so that the flask may be a quarter full, say. Cork the flask tightly. The boiling stops; and the upper three fourths of the flask are full of vapor. Squirt a jet of ice-cold water upon the flask, above where the water is, and the water below will instantly begin to boil. The reason why, is this. The vapor in the flask presses on the surface of the hot water. The cold condenses the vaporturns it back to water. That takes off the pressure for the time; and then the hot water directly flies into vapor, and boils, and so on, till it cools down too low to boil any