ttle 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-up--confined, 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