220 MAGNUS ON THE EXPANSIVE FORCE OF STEAM. 
have been made by measuring the pressure which vapour exerts 
in a confined space. Lither the steam has been allowed to act 
against a piston, as in the researches of Christian*, and the 
weight determined which it was capable of raising at different 
temperatures, or, as in those of Arzberger +, the force measured 
with which the steam at various pressures raised a globular valve. 
Such experiments can only be employed to ascertain the expan- 
sive force for temperatures above 100°, and moreover can only 
be of importance for the practical arts. And lastly, the expan- 
sive force of steam has been measured by the height of acolumn 
of mercury holding this expansive force in equilibrium. 
Zieglert was the first who performed some experiments in 
this manner, and published them in the year 1768; they are 
however very deficient, and bear in this respect no comparison 
with those made by Watt at Glasgow in the winter of 1764-65, 
which, however, were published by him at a far later period 
(1814) as an Appendix to the article Steam in Brewster’s edi- 
tion of Robison’s ‘ System of Mechanical Philosophy’ §. Similar 
investigations exist by Robison||, Betancourt**, G.G.Schmidttf, 
Biker of Rotterdam ¢}{, Southern $§, Dalton |||| and Ure***; and 
moreover some isolated observations by Gay-Lussactt}, Au- 
gustt{{t and others, as well as some determinations of the ex- 
pansive forces at low temperatures by Kamtz$§§, Prinsep |||||| 
and others by comparison of barometers, one of which contained 
water in its vacuum. 
The experiments of Biker were made only for temperatures 
higher than the boiling-point of water; those of Robison, Be- 
tancourt and G. G. Schmidt are older and less trustworthy, as is 
already evident, from their having assumed that steam at 0° 
had no expansive force. Such is not the case with respect to 
the experiments of Watt, Southern, Dalton and Ure; all four 
* Méchanique Industrielle, ii. 225. 
+ Jahrbiicher des Polytechnischen Instituts in Wien, i. 144. 
+ Specimen Physico-chemicum de Digestore Papini, p. 27. 
§ Vol. ii. p. 29. || Zbed. p. 238. 
** Mémoire sur la Force Expansive de la Vapeur. 
++ Gren’s Neues Journal, iv. 151. tt Gilbert’s Annalen, x. 257. 
§§ In Robison’s System of Mechanical Philosophy, ii. 170, 
\||| Memoirs of the Literary and Philosophical Society of Manchester, v. part 
2. p. 553; in his New System of Chemical Philososophy, second edit., 1827 ; 
and Encyclopedia Britannica, vol. xx. part 2. p. 599. 
*x** Phil. Trans. for 1818, p. 338. ttt Biot, Traité de Phys., i. 287. 
tt Poggendorff’s Annalen, v. 344. §§§ In his Meteorologie, i. 290. 
\\Il|| Journal of the Asiatic Society of Bengal for April 1833. 
