whizzing of shrapnel over our heads.

I, too, soon got accustomed to the deadly missiles,--in fact, I had
already started to make observations of their peculiarities. My ear,
accustomed to differentiate sounds of all kinds, had some time ago,
while we still advanced, noted a remarkable discrepancy in the
peculiar whine produced by the different shells in their rapid flight
through the air as they passed over our heads, some sounding
shrill, with a rising tendency, and the others rather dull, with a falling
cadence. A short observation revealed the fact that the passing of
a dull-sounding shell was invariably preceded by a flash from one of
our own cannon in the rear on the hill, which conclusively proved it
to be an Austrian shell. It must be understood that as we were
advancing between the positions of the Austrian and Russian
artillery, both kinds of shells were passing over our heads. As we
advanced the difference between shrill and dull shell grew less and
less perceptible, until I could hardly tell them apart. Upon nearing
the hill the difference increased again more and more until on the hill
itself it was very marked. After our trench was finished I crawled to
the top of the hill until I could make out the flash of the Russian guns
on the opposite heights and by timing flash and actual passing of
the shell, found to my astonishment that now the Russian missiles
had become dull, while on the other hand, the shrill shell was
invariably heralded by a flash from one of our guns, now far in the
rear. What had happened was this: Every shell describes in its
course a parabolic line, with the first half of the curve ascending and
the second one descending. Apparently in the first half of its curve,
that is, its course while ascending, the shell produced a dull whine
accompanied by a falling cadence, which changes to a rising shrill
as soon as the acme has been reached and the curve points