170 On the Ufe of Steam as a Vehicle for conveying Heat. 



ftrength of the tube will be more than doubled by this covering, I found by experiments, 

 the mod unexceptionable and decifive, of which I intend at fome future period to give to 

 the public a full and detailed account, that the ftrength of paper is fuch, when feveral 

 iheets of it are firmly attached together with glue, that a folid cylinder of this fubftance,. 

 the tranfverfe fediion of which (hould amount to only one fuperficial inch,, would fuftain a 

 weight of 30,000 lbs. avoirdupois, or above 13, tons, fufpended to it, without being pulled 

 afundcr or broken. The ftrength of hemp is ftill much greater, when it is pulled equally^ 

 in the dire£Vion of the length of its fibres. I found, from the refults of my experiments 

 with this fubftance, that a cylinder of the fizc above mentioned, compofed of the ftraight 

 fibres of hemp, glued together, would fuftain 92000 lbs. without being pulled afunder. 



A cylinder, of equal dimenfions, compofed of the ftrongeft iron I could ever meet with, 

 would not fuftain moie than 6i5ooo lbs., weight j and the iron muft be very good not to be 

 pulled afunder with a weight equal to 55000 lbs. avoirdupois. 



I (hall not, in this place, enlarge on the many advantages that may be derived from a 

 knowledge of thefe curious fa(fls. I have mentioned them now in order that they may be 

 known to the public ; and that ingenious men, who have leifure for thefe refearches, may 

 be induced to turn their attention to a fubje£t, not only very interefting, on many accounts, 

 but which promifes to lead to moft important improvements in mechanics. 



I cannot return from this digreflion without juft mentioning one or two refults of my 

 experimental inveftigations relative to the force of cohefion, or ftrength of bodies, which, 

 certainly, "are well calculated to excite the curiofity of men of fcience* 



The ftrength of bodies of different fizes, Jtmilar inform^ and compofed of the fame fuh- 

 flancey or the forces by which they refift being pulled afunder by weights fufpended to 

 them, and afting in the direction of their lengths, — are not in the ftmple ratio of the areas of 

 their tranfverfe feBions, or ol thz'ii fraElures : but in a higher ratio; and this ratio is dif- 

 ferent in different fubftances. 



The form of a body has a confideraHe influence on its ftrength, even -when it is pulled in 

 the dlreEiion of its length. 



All bodies, even the moft brittle, appear to be torn afunder:., or their particles fcparated, 

 or fibres broken, one after the other ; and hence it is evident, that that form muft be moft 

 favourable to the ftrength of any given body, pulled in the dircftlon of its length, which 

 enables the greateft number of its particles,, or longitudinal fibres, to be feparated to the 

 greateft poiTible diftance— ftiort of that at which the force of cohefion is over<;ome, — before 

 any of them have been forced beyond that limit. 



It is more than probable that the apparent ftrength of diflferent fubftances depends much 

 more on the number of their particles that come into a£tion before any of them are forced 

 beyond the limit of the attraftion of cohefion, than on any fpecific difference in the inten- 

 fity of that force in thofe fubftances. 



But to return to the fubje£l more immediately under confideration. — ^As it is effential 



that the fteam employed in heating liquids, in the manner before defcribed, fhould enter 



4 the 



