New-York tribune., 1873-05-06

nothino mathematical nothing that has 10 be guessed
Bridge building is science OF very great perfection, and
has had its development In the hands Of very superior
class OF scholars and engineers There has probably
been no one field OF industrial enterprise that called
into its service q greater amOnnt OF intellectual effort
than mat embraced In iron constructions OF ali kinds
and in no other branch Of industry commensurate with
It. does little knowledge prove 30 dangerous "a thing
enees simply being in price, the for such differ
ence being due 10 the greater or less greed OF the
tractor Ine Pfee o. OTog ro of y an oy
ore the furnace and the working and varies In quality
with the smallest modification IN each particular. Tie
loads for which bridge is proportoned the fitting OF
the jonts the margin for safety, all have their in-
enee in determining the worth Of such structure.
ty OF certain class Of socaed bridge builders the case
of one such VINO applied To prominent engineer for a
formula 20 compute the center mongre style
of bOwstrinG girder which he had been building for
long time dt happened tlat fhe engineer alluded to
ing down such girder by weighting with pig
of pencing on the hack of an envelope showed that
the grder should have been broken under the imposed
turned TO the gentleman who made the above note with
the remark: " You don't say that you can figure out
now much a bridge can standi 1 wish Won wonId sten
up to the office and tell my draughtsman how 10 do IT,
We never figure up our bridges, aud did not know It
could be done" And yet this man had for several
been building "IrOn Bridges for the People," as he
headed his circulars and had driven every reputable
took work for about half the price It should have cost
About the bridge which Iell l know nothing, but
assume on the strength OF the figures given by YOU that
1t was miserable, iproporticned affair, ana should
have fallen. You give It's length 200 rods $500 feet
aud the cost as $4,000 Letting masonry alone enirely
and assuming ordinary spans, iron bridge OF that
length could not be properly built for twice tho money
poor iron bridge ia infinitely than a pIOr
wooden one, aud thuk there Is little doubt
hundreds OF bridges throughout the country
stand SIMPLY because the loads them occasional
aud far very tar within what bridge should be pro-
portiOned for. The infrequont crossing OF toam IL
probably oil they exposed 10, hut should crowd
collect on extraordinary occasion, in tue Of
the Illinois bridge, the result is easy " forecast
Raj road bridges rarely II intTustcd 10 tho
hands Of such builders, aud they shrcwd enough To
waste no time looking after them; and aIn glad be-
eye That there are few counties who Will under
circumstances consider the bids OF what be strictly
denOmnated tne tin-pdn interest" Legislative enact
ment might be obtained tO protect the people, by de-
termnng the standard OF strength rds quality
OF ma1eTl loads to BE- carried, and work.
manship. Tnere Is contingency, however, wben one
consuer5 the manner IN when technical legislation 10
apt ~ be performed that the experts" VINO would BE-
called Ia u give the necessary Ormlton ON which TO
the legislation, viii be FROM tnat class tuat have
taken this To condemn. Modern politics and
npan bridges have ths Ia common they apt to De
pursued by tne same class o. men.
ieC-lO ORR, May g. 1873. ALE L. BOILER, Cvll Enga'r.