4*2 
Mr. de Luc 
steam is arrived at its maximum ; for that fluid is then so 
ready to abandon its water, if this has a tendency elsewhere, 
that a small quantity of new steam introduced in the space, 
. would occasion the decomposition of part of it, followed by a 
spontaneous precipitation of water. 
10. But we have seen above, that steam arrives to its 
maximum with different degrees of density, according to the 
temperature ; consequently, whatever be the actual density 
of steam, if that density is its maximum conformable to the 
temperature, the hygroscopic body will receive water to the 
maximum ; and thereby it will attain its maximum of 
length. 
11. Now, as according to the premises, the density of steam 
is not the only circumstance by which, at the last period, the 
hygroscopic body retains in a medium the maximum of water 
that it can receive, that effect depending also on the tempera- 
ture ; by the same cause, the density of steam is not at the 
former periods, the only circumstance which determines the 
quantity of water that the hygroscopic body can retain in 
the medium ; that quantity depends also on the temperature. 
The following is the theory of that phenomenon, or of the 
hygroscopic equilibrium between the medium and bodies. 
12. In consequence of the above determined composition of 
steam, whatever be its quantity in a given space, either filled 
with air or free from it, its aptitude of communicating wa- 
ter to hygroscopic substances, is always proportional to the 
actual ratio between that quantity and the maximum cor- 
respondent to the temperature ; which ratio, and not an ab- 
solute quantity of steam, is a certain degree of moisture con- 
sidered in the medium ; whereas moisture considered in a 
