Q. _Why is NOT RAIN-water SALT, although most of it is evaporated from the SEA?_ A. Because _salt will not evaporate_; and, therefore, when sea-water is turned to vapour, its _salt is left behind_. Q. _Why does STAGNANT water PUTREFY?_ A. Because leaves, plants, insects, &c. are decomposed in it. Q. _Why is STAGNANT water full of WORMS, EELS, &c.?_ A. Because numberless insects _lay their eggs_ in the leaves and plants which float on the surface; these eggs are soon hatched, and produce swarms of worms, eels, and insects. Q. _Why are FLOWING waters FREE from these IMPURITIES?_ A. 1st--Because the motion of running water _prevents its fermentation:_ 2ndly--It _dissolves the putrid substances_ which happen to fall into it: and 3rdly--It casts _on the bank_ (by its current) such substances as it cannot _dissolve_. Q. _Why does RUNNING water OSCILLATE and WHIRL in its current?_ A. 1st--Because it _impinges against its banks_, and is perpetually diverted from its forward motion: and 2ndly--Because the _centre_ of a river _flows faster_ than its _sides_. Q. _Why do the SIDES of a river flow more TARDILY than its CENTRE?_ A. Because they _rub against the banks_, and are delayed in their current thereby. Q. _Why does SOAPY water BUBBLE?_ A. Because the soap _makes the water tenacious_, and prevents the bubbles from _bursting_ as soon as they are formed. Q. _Why will not water bubble WITHOUT SOAP?_ A. Because it is not tenacious enough _to hold together the bubbles_ that are formed. Q. _When SOAP BUBBLES are blown from a pipe, why do they ASCEND?_ A. Because they are _filled with warm breath_, which is lighter than air. CHAPTER XXVI. ICE. Q. _What is ICE?_ A. FROZEN WATER. When the air is reduced to 32 degrees of heat, water will no longer remain in a _fluid state_. Q. _Why is SOLID ICE LIGHTER than WATER?_ A. Because water _expands by freezing_; and as the _bulk is increased_, the _gravity_ must be _less_. Nine cubic inches of water become ten when frozen. Q. _Why do EWERS BREAK in a FROSTY NIGHT?_ A. Because the water in them _freezes_; and as the _water is expanded by frost_, it bursts the ewers to make room for its increased volume. Q. _Why does it not expand UPWARDS (like boiling water), and RUN OVER?_ A. Because the _surface_ is first frozen, and the frozen surface acts as a _plug_, which is more difficult to burst than the earthen ewer itself. Q. _Why do TILES, STONES, and ROCKS often SPLIT in winter?_ A. Because the moisture (which they imbibed) _freezes_, and by its expansion _splits the solid mass_. Q. _In winter time, FOOT-MARKS and WHEEL-RUTS are often covered with an icy NET-WORK, through the interstices of which the soil is clearly seen,--WHY does the water freeze in NET-WORK?_