A. When a cloud, _overcharged_ with electric fluid, approaches another which is _under-charged_, the fluid rushes from the former into the latter, till both have the same quantity. Q. _Is there any OTHER cause of lightning, besides the one just mentioned?_ A. Yes; sometimes mountains, trees, and steeples, will discharge a lightning cloud floating near; and sometimes electric fluid rushes out of the _earth_, into the clouds. Q. _What produces ELECTRICITY in the CLOUDS?_ A. 1st--The evaporation from the earth's surface. 2ndly--The chemical changes perpetually going on: and 3rdly--Currents of air of unequal temperature, excite electricity by _friction_, as they pass by each other. Q. _How HIGH are the LIGHTNING-CLOUDS from the earth?_ A. Electrical clouds are the _lowest of all clouds_; they are rarely more than 700 yards above the ground; and sometimes, they actually _touch the earth_ with one of their edges. Q. _How high are the clouds generally?_ A. In a _fine_ day, the clouds are often 4 or 5 miles above our head; but the average height of the clouds is from 1-1/2 to 2 miles. Q. _Why is lightning sometimes_ FORKED? A. When the lightning-cloud is a long way off, the _resistance of the air_ is so great, that the electrical current is diverted into a zig-zag course. Q. _Why does the resistance of the air make the lightning zig-zag?_ A. As the lightning _condenses_ the air, in the immediate advance of its path; it keeps flying from side to side, in order to pass where there is the _least resistance_. Q. _How does lightning_ CONDENSE _the air in the immediate advance of its path_? A. The air is condensed by the _rapidity_ of the lightning-flash. Q. _Why is_ FORKED LIGHTNING _more_ DANGEROUS _than a straight flash_? A. Whatever _resists_ the flash, _diverts its course_; and when _terrestrial_ objects offer resistance to the current, they are in great danger of being destroyed. Q. _Why are there sometimes_ TWO _flashes of forked lightning at the same moment_? A. Sometimes (in very severe storms) a flash of lightning will divide _into two or more parts_; and then each branch assumes the zig-zag form. Q. _Why is the FLASH sometimes quite STRAIGHT?_ A. When the lightning-cloud hovers _near the earth_, as the flash meets with very little resistance, it is _not diverted_; or (in other words) the flash is straight. Q. _What is the cause of_ SHEET LIGHTNING? A. It is only the _reflection of distant flashes_, not distinctly visible: and sometimes several flashes (from different clouds) intermingle, and form one vast blaze or sheet of lightning. Q. _Which_ FORM _of lightning is the most_ DANGEROUS? A. The _ball_ of fire is by far the most dangerous; and the _zig-zag_ lightning is next in danger. _Sheet_ lightning is not often attended with danger. Q. _Why are_ BALLS OF FIRE _so very dangerous?_