[ IZ7 ] 
the water is afterwards gradually aflluxiing the form of 
ice, we know, by experience, that the temperature of it 
muft remain at 3 2°; it cannot be made colder, fo long as 
any conliderable part of it remains unfrozen''"^. The re- 
frigerating caufes continue, therefore, to have power over 
it, and to act upon it, and will gradually change the whole 
into ice, if their a6tion be continued fufficiently long. 
The next objedt of inveftigation may be the caufe 
of this difference between the boiled and the common 
water. In confidering this point, the following idea 
was fuggeffed. As we know from experience, that by 
dilturbing common water, we haften the beginning of 
its congelation, or render it incapable of being cooled 
below 32°, without being congealed; may not the only 
difference between it and boiling water, when they are 
expofed together to a calm frofly air, coniift in this cir- 
cumftance : that the boiled water is neceffarily fubjedled 
to the adlion of a dihurbing caufe, during the whole 
time of its expofure, which the other is not ? One effedt 
of boiling water long, is to expell the air which it natu- 
rally contains ; as foon as it cools, it begins to attradl and 
abforb air again, until it hath recovered its former quan- 
tity ; but this probably requires a conliderable time. Du- 
ring the whole of this time, the air entering into it muff 
occaffon an agitation or diffurbance in the water, which, 
though not fenffble to the eye, may be very effedtual in 
{a) Common water, when cooled in a ftate of tranquillity to feveral degrees 
below the freeing point, will fuddenly rife up to it again, if difturbed in fuch a 
manner as to occafion in it a beginning of congelation. 
preventing 
