A. As soon as the pie is put into the oven, the _air_ in the cup will _begin to expand_, and drive every particle of juice from under it; the pie dish, therefore, will have a cup-full _less room_ to hold its fruit, than if the cup were _taken out_. Q. _If the juice is driven OUT of the cup, why is the CUP always FULL of JUICE, when the pie is cut up?_ A. Immediately the pie is drawn, the _air_ in the cup begins to _condense again_, and _occupy a smaller space_; in consequence of which, there is no longer _enough air to fill the cup_, and so _juice_ rushes in _to fill up the deficiency_. Q. _Why does JUICE rush into the cup, because the cup is NOT FULL of AIR?_ A. As the external air _presses upon the surface of the juice_, it rushes into the cup _unobstructed_; as mercury rises through the tube of a barometer through similar pressure. CHAPTER X. EXPANSION FROM HEAT. _(Continued.)_ Q. _Does heat expand every thing ELSE BESIDES air and water?_ A. Yes; _every_ thing (that man is acquainted with) is expanded by heat. Q. _Why does a COOPER make his HOOPS RED-HOT, when he puts them on a tub?_ A. 1st--As _iron expands by heat_, the hoops will be _larger_ when they are red-hot; and will, therefore, _fit more easily on the tub_: and 2ndly--As _iron contracts by cold_, the hoops will _shrink_ as they cool down, and _girt the tub with a tighter grasp_. Q. _Why does a WHEELWRIGHT make his hoops RED-HOT, which he fixes on the NAVE of a WHEEL?_ A. 1st--That they may _fit on more easily_: and 2ndly--That they may _girt the nave more tightly_. Q. _Why will the wheelwright's HOOP FIT the nave MORE EASILY, because they are made RED-HOT?_ A. As _iron expands by heat_, the hoops will be _larger_ when they are hot; and (being larger) will go on the nave more _easily_. Q. _Why will the HOOPS, which have been PUT ON HOT, girt the nave more FIRMLY?_ A. As _iron contracts by cold_, the hoops will _shrink as they cool down_; and, therefore, _girt the nave with a tighter grasp_. Q. _Why does a farrier put the HORSE-SHOE on HOT?_ A. That it may _stick the closer_, when it has contracted by cold. Q. _Why does a STOVE make a CRACKING NOISE, when a fire is very hot?_ A. The iron stove _expands by heat_, and (as it swells) the parts rub both _against each other_, and _against the bricks around_, driving them further off; and this produces a _cracking_ noise. Q. _Why does a STOVE make a similar CRACKING NOISE, when a large FIRE is TAKEN DOWN?_ A. The iron stove _contracts again_, as soon as the fire is removed; and (as it shrinks into a smaller space) the parts _rub against each other again_, and the _bricks are again disturbed_; and this produces a cracking noise. Q. _Why does the PLASTER round a STOVE CRACK and fall away?_