Daily globe. [volume] (St. Paul, Minn.) 1878-1884, 1883-06-21

ana constructing the bridge. Mr.. w. IS.
Sheehan, from daily observation of the
bridges referred to was convinced Of their
senseable economy, and thought Mr.. Law
Ter entitled to a great deal of credit for
developing that kind OF engineering. Mr..
Whittemore stated some facts as to the
history of railway pontoou bridge build
ing, which came under his observation
when Henry R. Campbell put potion in at
Rousen's Point (outlet of Lake Cham plain,)
fer the Vermont Central, which was operated
for nineteen years, without interruption.
by dismantied Baldwin No. 4 locomotive
That pontoon was 800 feet long, Mr.. Law
ler's was 408 feet. The variation of water
at Rouse's Point is only 6 to s feet, at
Prairie du Chen it is three times as great
He concluded by disclaiming credit for the
Lawler bridges, which, he said Mr.. Lawler
deserved wholly. Mr.. Lawler explained
that full trains, drawn by the largest en-
gines, pass over the bridges
without separating; that passen
gers will not notice any change Of level,
and that only close observer on the out
side would see it. The large floating ca
pacity is of course obtained from the i'm
mense size of the pontoons, which are
opened for the river craft inside of three
minutes.
THE MONONGAHELA BRIDGES.
Mr.. c. Lindenthal, of Pittsburg, by the
aid of drawings, explained his building of
the new steel bridge over thess Monongahela
at South Pittsburg. The first bridge On
the site, constructed of wood in 1916, was
1,SOS feet long, and stood until it was de-
stroyed by fire about 1914. In 1915 when
the PRESENT theories of wire or suspension
bridges were yet to be evolved the
elder R9bling John A. constructed sus
pension bridge on the spot, and the present
bridge was built in 1SS1-'S3. The old sus-
pension bridge was fully described, and
also its condition when the new bridge
was built This was done, the new one be-
ing foOred twenty feet higher, with only
one and half days interruption of traffic.
The expedients to prevent interruption of
traffic were explained and the heavy char
acter of the tratfice was mentioned to show
| the necessity of such bridge as the new
| one. Then followed lengthy statement
of tests of the iron which had been in use
IN the suspension bridge for thirty seven
years, and the condition in which all parts
of the iron work Of the bridge were found
when uncovered. The advantages of the
| wire cable were proven by this bridge and it
was maintained that there had been no de-
terioration of the iron by strain or from
ordinary vibration. Lumber in the bridge
which had been covered from sun and rain
for the Jhirty-seven years was found in ex-
cellent condition. Mr.. Collinwood, COM
! menting upon the wave like
motion of the old cables
at Pittsburg preceding heavy load, re-
lated his late examination Of the great
| suspension bridge over East River, when
| three heavily loaded trucks, moving at
| trotting speed, did not produce a wave
motion on ..the cables Hence he held
that the weight of the cables is
| an element Of stability. These cables are
sixteen inches IN diameter, yet very sensi-
| tive, showing that the trusses &c, are do
| ing their work. He regarded the elder
| Roebling as very successful in distributing
weights, and to this attributed the life of
| the Pittsburg bridge under the conditions
described by Mr.. Lindenthal. He did not
| think the texture of iron would be changed
| by the ordinary vibrations Or jar Of bridge.
DR.. Eggleston, referring to the weakness
| of some of the iron in the old bridge, re-
| marked that one cause of weakness is de-
fective annealing instead of defective
metal. great many of the annealing
furnaces, he said, really lnjure the metal.
A colloquy followed rega riding the crystal
lization or granulation of metals, Mr..
| Lindenthal having described some breaks
as showing crystalline fractures, and others
as showing a granular change in the
metal. Mr.. Lindenthal claimed that under
the microscope there were differences
shown, crystals appearing in one case and
uncrystallZed granules in another. Dr.
: Eggleston remarked that nearly all iron
contains more or less Stag. Mr..
Collinwood, commenting upon the strain
borne by the small irons Of Roebling's
bridge, referred to papers of the society
in which the elasticity of metal is dis
cussed, and in which it is shown that
metal which has been overstrained without
break seems to have thus had its elastic
limit raised.
| A SOUVENIR.
At the conclusion of this discussion. Just
before adjournment, the secretary and
volunteer assistants distributed to the
members of the society a souvenir of it's
meeting IN Minnesota, in form of book
containing number of views on
and about St. Paul and Mime
apolis and brief description and
historical sketches of the two cities. This
was prepared by the joint local committee
and viii doubtless be priced souvenir of
the assembly of '83 to all the members.
The books were all IN sealed wrappers and
the reporters had to take the word of one
of the committee, that they are handsome
and all they should be.
The society at 1870 this morning will
receive and discuss a report Of its commit
tee Oh pending propositions for uniform
standards of time.