to determining the magnitude of material 'particles. 15 
I do not think it could be conducted to the requisite point of 
closeness without an opposite result taking place to the open- 
ing of the pores of Staffordshire ware by intense heat, namely, 
a closing up of all pores by a vitrification of the body; the 
Chinese ware being evidently very siliceous, and corre- 
sponding in its transitions with mixtures I have already re- 
ferred to. 
There is a brown stoneware manufactured in a large pot- 
tery at Helper in Derbyshire, which, from certain qualities, 
I should judge to be formed of a body likely to yield, at dif- 
ferent degrees of heat, the several approximations of parts 
suited for these experiments, provided it were protected from 
a glazing of the surface, which would cause an imperfect re- 
sult, though no glazing is impermeable by fluids under press- 
ure. And it is proper to remark, that although I have de- 
scribed only four degrees of density, they were selected out 
of several yielding intermediate results; which would be re- 
quisite before the heat for the experiments were obtained. 
These remarks may not appear irrelevant, since they may 
serve as some guide to a person desirous of repeating or ex- 
tending the experiments. 
The familiar fact that water may be retained in a porous 
earthen pitcher for a length of time without any escaping ex- 
cepting by evaporation, although the lower part is under the 
pressure of a foot or more of the fluid, while such a pressure 
would suffice to force air quickly through the pores, would 
commonly be explained by supposing a greater minuteness of 
parts in tne case of air than of water; but the above experi- 
ments would prove the contrary. 
The right explanation is to be found in the case of the li- 
quid, in the cohesive attraction between the particles which 
indispose the liquid to that breaking up into minute portions 
requisite before it can enter the pores, and where it has en- 
tered the pores in the capillary adhesion to the substance 
of the ware by which the liquid refuses to leave its outer 
surface and run down ; while in the case of the gaseous fluid 
a mutual repulsion favours the separation of its particles, and 
there is no considerable attraction between them and the earthy 
surfaces to resist their passage out ; the greater subtilty of 
the air over the water being due to these causes and not to its 
being composed of minuter particles. In some measure re- 
lated to this subject I had to notice some interesting facts 
connected with the transmission of saline liquids through 
woody fibre, but the space of this paper does not admit of their 
being detailed here. 
Julius Jeffreys. 
