The Irish standard., 1899-02-04
INVENTION OF PROF. ZAHM, OF THE
CATHOLIC UNIVERSITY.
MACHINE OF INGENIOUS CONSTRUCTION
MEASURES A HUNDRED MILLIONTH
PART OF A SECOND.
THE LAW OF ATMOSPHERIC RESISTANCE
DETERMINES ALL vELOCITIES FROM
LOWEST TO HIGHEsT.


The most curious cannon, perhaps, in
the world has been recently cast at
South Bend. Ind, for the use of Prof.
A. F. Zahm, of the Catholic University
of America, at Washington, D. G. 1t is
intended to shoot hollow bullets larger
than croquet balls and thin as egg
shells. These are to be aimed. not at
Spaniards nor Spanish Notifications. but
at the blank atmosphere, to determine
new law in physical science.
Architects and engineers have wished
for generations to know, when design
ing buildings, bridges and other struct-
ures, how to calculate the pressure of
the wind against them, especially In
violent storms, which are critical tests
of stability; but there has been no relia-
BILE rule to guide the designer, and SO
great many experimenters have tried to
measure the force of the wind at high
velocities. Military engineers, too, have
many times attempted, with the most in
genious instruments, to find the pressure
of the air in front Of projectiles; but
their results have not agreed, especially
for speeds below a thousand feet Sec
ond. So DIR. Zahm has invented entirely
new methods and most accurate instru-
ments by which he has succeeded in
making measurements which have baf
fled the skill of all the military experts
Of the foremost nations.
DR.. Zahm observed, at the beginning
of his research, that the methods en-
ployed by the military engineers of the
various governments were defective in
several features, some of which are of
cardinal Importance in the determine
tion of atmospheric resistance. For
example, the experiments were usually
made out of doors where there is always
some breeze or movement in the air in
dependent of the projectile's motion,
thus making the measured resistance
sometimes greater, sometimes less, with
the same projectile velocity. Again, the
ordinary projecties employed are dozens
of times too massive to make the resist
ance in front Of them very apparent,
for, since this resistance is manifested
by the slowing up of the bullet, the lat
ter should be as light as possible with
out collapsing or straining. And most
notable of all, the chronographs used to
measure the slowing up Of the project
lies during their rapid flight were all in
adequate to achieve accurate results,
many of them not being competent to
precisely measure one-thousandth of a
a second whereas it is desirable that
of one-thousandth of second.
To overcome these difficulties and at
tain scientific precision meant to aban-
don all the government methods to de-
wise new system and invent new in
struments. This the professor has done
from beginning to end of his marvellous
ly accurate apparatus. He has located
the gun, target and chronograph in a
temperature and barometric pressure are
observed at each shot. He uses hollow
steel projecties which are SO times as
light as the ordinary solid ones, thus
making their retardation during fight
so times greater, and hence so times as
easy to measure. He uses chrono-
graph which records and measures a
| milliOnth of a second more accurately
than common watch can measure the
| second.
The very curious design of Prof.
Zahm's canon is demanded by the ex-
| treme ilghtness of the projectiles to be
| fired from it. Though they are four
inches in diameter, they weigh but four
or five ounces, and require hardly an
| ounce Of smokeless powder to give them
| speed Of 500 miles an hour. This
powder is contained in common shot
gun, whose barrel is cut down to about
six inches in length and permanently
screwed into the breech of the cannon,
thus presenting the curious spectacle of
common bird gun shooting bullet
larger than croquet ball. Another odd
| feature of this scientific cannon is it's
muzzle end. The whole cannon is 20
| feet long, the first six feet from the
breech having common smooth bore,
| but the next Il feet being so full Of big
holes that it looks like an elongated
squirrel wheel. In the first part the
powder gives the bullet It's full speed,
while in the second part the gases rush
out sidewise through the spacious open
ings. and die down 80 completely that
the shell, on emerging from the muzzle,
passes onward through perfectly still
air-so still. In fact. that newspaper
held near the muzzle does not percepti-
bly, futter when the cannon is fired.
Evidently without this open structure
the gases would follow the bullet to a