maller drops and, therefore, a great deal of electricity is
set free.

"Only a few flashes of lightning reach the earth. Most lightning-flashes
occur between two cloud masses in the body of the thunder-cloud.
Photographs of these show them to consist of scores of fine branches
which jump from one cloud to the other, the flash being strong or weak
according to the distance to be jumped. You can see that a very faint
flash could jump a distance of an inch, but that it would take a
stronger current to jump a yard, and that a terrific force of
electricity must have accumulated before the current is strong enough to
break down the resistance of the non-conducting air and jump a quarter
of a mile. When lightning is attracted by the earth, it means that the
air between the thunder-cloud and the earth is being subjected to a
constant strain, and the weakest place gives way first. The weakest
place, generally, is the place when the jump is shortest and there is a
good conductor available.

"One of the reasons that buildings and trees are struck by lightning is
because they project up into the air, and according to their height,
they remove a corresponding amount of the poorly conducting air. If the
lower edge of a thunder-cloud is two thousand five hundred feet above
the air, and the spire of a church is five hundred feet high, it follows
that it is easier for a flash to jump two thousand feet than two
thousand five hundred. So when the electricity-bearing cloud comes over
the church spire the flash will leap to the church, five hundred feet of
obstacle being removed. The highest building, therefore, is usually
struck first, or the highest tree in a forest.

"A lightning-rod or conductor is the best preventive against the
destruction of a building by lightning, if the rod sticks up in the air
above the building, even a couple of feet. The current will more readily
strike the lightning-rod. As these are made of metal--copper or iron,
generally--which are extremely good conductors, the current flows
through them to the ground without harming the building.

"The big lightning flashes that you see, boys, aren't always a single
flash, but often a whole series of flashes, which occasionally run up as
well as down. The resistance of the air being broken down, makes a path
for the electrical discharge, so that the conductor does not have to
stand the entire strain of the cloud at once, but only in a series of
discharges. Photographs