Rensselaer Union, Volume 7, Number 33, Rensselaer, Jasper County, 6 May 1875 — Effects of Heat and Cold. [ARTICLE]

Effects of Heat and Cold.

The Railway World presents several interesting facts regarding the effects of heat and cold on the St. Louis bridge, from which the following is condensed: The arches of this bridge are 500 feet long. In their construction allowances were made for the extremes of temperature through a range of 140 deg.—that is, from the greatest cold in winter to the warmest day in summer. It was calculated that the difference in elevation of the center arch of the upper cord in these two ex“tremes of temperature would be about eighteen inches. Since these calculations were made opportunities for actual experiment have been abundant, and have been improved, to test the value of the original calculations, as well as to determine the actual effect of these changes in temperature. The following table gives certain results of these observations, the height here noted being that of the center pier of the top chord above the City Directrix: .a. May 6.1874 69 = Fahr. 63.548 June 29,1874 77 o Fahr. 68.4§8 July 20, 1874 91= Fahr. 63.757 Jan. 4, 1875 10= Fahr. 63.241 Jan. 9, 1875 150 Fahr. 68.065 Beween the figures for July 20 and those for Jan. 9, which two days are respectively the warmest and coldest of the year, there is a difference in temperature of 107° Fahr., and in height* of center arch of .692 of a foot. This is an effect of temperature much less than calculated, due partly to the fact of the iron work being painted white, which lessens the absorp tion of heat in hot weather and increases the radiation in cold weather, and also the protection afforded by the roof ot the bridge. This latter is strikingly exemplified in the fact that the river, while frozen above and below the bridge, has yet been open under it —The Postmaster of Monticello, Ga., recently performed the feat of reading a letter without hearing its contents. An old woman who had never been to school got a letter one day and asked the Postmaster to read it for her. She did not want him to hear it, so she took a wad of cotton out of her pocket and stuffed his ears with it. She then had him read the letter in a low voice and was perfectly satisfied that the reader could not hear a word of it. This is reported as a late actual occurrence, but it is one of those things that used to happen (in newspapers) when the oldest of us were boys.