The Saint Paul globe. (St. Paul, Minn.) 1896-1905, 1903-03-23
Special to The Globe.


| BOSTON, Mass, March 22-The law
| Of breakages is still unknown and IN
written. This twentieth century-the
| age of machinery-notwiths landing its
wonderful structures, it's ingenious in
Ventions and it's brilliant mechanical
| discoveries, still leaves unanswered the
| question of how long a thing will last
and at what moment it will break-un-
| eXpectedly and under no ususual strain
and our most advanced mechanical
laboratories are still experimenting with
| structural materials, cropping for a sat
| iSfactory conclusion.
A freight car will pound along over a
few hundred thousand miles of rough
road with apparent Indifference; then,
some time when it is moving at a very
moderate speed, mayhap on exception
ally even rails, one of its hitherto sound
steel axles breaks short off and a dis
astrous train wreck is the result. SINH
larly, a steamship fights out many a
gale, laboring against heavy seas with
her screw thrashing out of water. and
afterward, in fine, still weather. breaks
her propeller shaft as if it were a pipe
stem and becomes a helpless hulk upon
the ocean.
A more striking instance is that of
the Brooklyn bridge, which, though I'M
doubtedly built of originally sound
materials, began to show signs of
weakness, even to the breaking of some
of its members after a certain num-
Der Of years, during which a certain
number OF cars and carts ran over it.
Evidently, II the laws governing these
apparently causeleSs breakages could
be discovered-and scientists feel con-
fdent that laws do not exist that de-
nne the endurance of all structural
| materials-many lives would be saved
and many tons of useless material,
which are now added to the contract
or's burden merely to secure a ran
dom factor for safety" could be elm
mated from the construction.
Seeks the Answer.
Among the many truth seekers. the
Massachusetts Institute of Technology
seems to be in a fair way toward
knowing the answer and as like as
not will be the first to come to definite
conclusions upon the matter. BY what
has already been found out in differ
ent Investigations from time to time
all mechanical scientists agree that
the metals with which we build and
on which we impose such heavy strains
have the same disadvantage of grad
ually firing out and finally giving way
as the perishable muscles and sinews
OF our own human bodies. Such is
the common hypothesis on which all
the experiments may begin; but as to
how soon, and in what conditions and
under how great a burden, this gradual
firing out takes place-that is what
we must know in order to prevent ac-
cidents.
The experiments at the Institute OF
Technology in the strength of materials
were begun by Prof. Gaetano LAMA
who is now in charge of the mechani-
cal engineering department, more than
twenty years ago. What was done be-
fore then was worked out on a small
scale, the theory being that if a piece
of wood two inches square showed GER
tain effects from q given test, another
piece two feet square, for example
would show similar effects in pro-
pOrtiOnate degree. Prof. LAMA, point
ing out that such differences were likely
to be incorrect on account of the vary
ing quality of different materials, be-
gan experimenting with full-siZed
beams and shafts and pillars such as
are used in the actual construction OF
buildings ard of machinery.
The methods of discovery In use in
the institute laboratories are both in
teresting and surprising. They disclose
one general fact very plainly; that the
| trial which structural materials above
all others cannot stand, is the trial of
| repeated Stress In other words, il
| the Brooklyn bridge, or any other steel
L
| ly full of the heaviest trains and We
! hicleS 1t was designed to carry and
| this load were to remain permanently
| upon it without ever being moved away
| the bridge would last DEMONSTRATING
rust. But put these same weights IL
| motion, SO that the entire structure
| trembles with their going, and the re-
| suit is very different indeed, because
| each member, instead of bearing q
steady fixed weight, undergoes a sue
| cession of little jerks answering to the
| vibration of the bridge as a whole. The
| brake-rods under a car work under
| similarly adverse conditions, for each
| time the brakes are put on they re-
ceive strain one way and each time
| they are released there is a strain IL
| the opposite direction.
A Different Case.
The case of the steamship shaft that
! breaks unexpectedly is somewhat diff
| ferent. Here a great steel rod-fol
| such it may be regarded-is turned
rapidly in one direction by the engine
| at the same time that it is twisted II
the opposite direction by the resistance
| of the water against the propelline
! screw. Being supported by either end
the shaft has tendency to sag
| the least bit somewhere, even though
it is held up by bearings, and it is evil
/ dent that wherever it bends, even evel
so little, its fbers are alternatel!
stretched and compressed. Now If thu