Law Of Heat--the Montreal Bridge

:;irronce of an accident on iuu of aur yre.U ruihvay, bócauae of the o iiiu.il j:i of the ruil uy the greut ■ ! . : , . :■■:■■: ty the extract ;i t'roai a lutter. Mr. llosa, the ensineep-in-cdjief of tlio strujturo, wan the writer ot the letter, and was a u iíl ut' greut sciijutiiio èxscüaess. xife Bumnier Buil of MufiTreal has a brief rcign, but it is of fcba vory liorcest wliilo it lasta. Tliose glittering tia xiofs of the city bc t'iili tbo mountaia retlect a ray ih:it sêe'ms to saorch all it tobcH. wLile iho viuissitudus of uliuiate brwgH ibither such cold ae, dij we enduro il ui Néw Vork, woulcl IVeozo the ivy o 11 Grace Ch'urch and uuiko statuarj of' tho swans in tho Park lake. It ia in uu liiiospliere thuí has terrible viIjratioi) tiiat tliis iron bridgo of moro tli-an a lui'e u;)d il half "u longth, is built. Jt is i góbd sobool - tho very bsst of pcboplsr-in (yliieh to note tho effect of i-Gilt extremos ia temperatura upon iron; a tu 1 kenoe Mr. llosa' oarefully preparod statement is the more valuable. Mr. Kjúís says : " Tlie tubes obey tbo hnvs eommou to iron in any sbapo or fórm by cootraoting or expandiug, as tho i;tse niíty bo ene ten-tbouáandth part of tho Íc:t!j for cch fifteeo degrees variáMOQ - Fahreuneit. Thus, from piar ttr pier tbe Victuriu tube extendí two hundred and ixty feet. It s, ua üiio pier, íixed - on theotber it is free t" move to iu:d frp. upon smooth rollers provided ír the purpos9 of rendering its obedieuce to these lnwseasy and uni' form. }fov instíince, two hundred and aixty feet of tubo gives ouu-thii'd oí an reoh as ono ten-thousandíh part of its length. In July last tbe thermometer indicated a maximum of 128. On tbe lOiíi and lltb of Janaary it marked 37 vo, inaking an extitmo variation of ÍJEÍ5. " Thi,: Jfoold produce a difference oí eleven ten-lbouruuiitlus part of the length o tuLe,""equal to tbree and twotiiirtis Eches, f.::c! this ís thc oxaet (juan tíiy found by ri.easureüjeiit to have been tlwi caso. The eótVema coid on tho days ïnentioued intluced more than ordinary caij to be taken, the low temperalure Imving roacted a point uaknown to tbe engit;er s-iuoo Lo lias bteu in this