484

Experiments with

[Book V.

—the particles of the fluid then being hurried along with a velocity toogreat to allow any of them to change their direction to escape at the leak.

The following abstract of experiments made by us in 1834-5, to illus-trate the same principle, may interest some readers:—To ascertain theextent to which atmospheric pressure was removed from under the sheetof paper, we bent a small glass tube at right angles, and placing one endunder the paper let it rest on the table, while the other descended into atumbler containing a litt.le water. Then taking a small pair of bellows,and directing the blast over the pipe, the water rose from one half to threefourths of an inch. The books upon which the sheet laid were then placedwithin two inches of each other, when the effect was increased, the liquidrising from lj to 2 inches. We next laid aside the paper and made useof two tubes, one to blow through and the other to measure the ascent ofthe liquid.

No. 203. No. 204.

No. 205.

No. 206.

No. 207.

No. 208.

No. 209.

No. 210.

Two leaden or block tin tubes, straight and polished in the inside, wereUnited at right angles. See No. 203. A C the blowing pipe, 8 incheslong and half-inch bore. B 12 inches long and three-eighths bore. Theupper end of B was joined flush and smooth with the interior of the other,three inches from the end A. Upon applying the mouth to C and blowingin the direction C A, indicated by the arrow, instead of the liquid risingin B, part of the current from the lungs entered that tube and was forcedthrough the water in the tumbler. Various portions of the end A werethen cut off without changing the result, und! half an inch only remainedin front of the joint, when the air no longer descended, but no rarefactionwas produced in B. When both tubes were made of the same bore, partof the blast descended in B until the whole of A in front of the joint wasremoved. In numerous trials, the water in the lower end of B was de-pressed more or less, whether the blast of wind through A was weak orstrong. (From these experiments we discover the impropriety of placingcylindrical tubes on chimney tops at right angles to the draft, and espe-cially on locomotive carriages, as was at first proposed. in the EdinburghEncyclopedia, vol. xvii. p. 457, a carriage by Tredgold is described, anda figure of it given in plate 511. The chimney is represented with a shorthorizontal tube attached fore and aft to the top, as in No. 203, with a view“ to assist the draft” by the passage of the air or wind through it. Theexperiments above show that the reverse would have been the case.)

As part of the air in passing through A, in No. 203, turned off into B,