for meafuring the higher Degrees of Heat , &c. giy 
water ; yet, when faturated with the water, their bulk con- 
tinues exactly the fame as in a dry {late. 
2. By very flrong fire, they are changed to a porcelain or 
femi-vitreous texture; nev.erthelefs, their contra&ion, on fur- 
ther augmentations of the heat, proceeds regularly as before, 
up to the higheft degree of fire that I have been able to 
produce. 
3. They bear fudden alternatives of heat and cold; may be 
dropped at once into intenfe fire, and, when they have received 
its heat, may be plunged as fuddenly into cold water, wfithout 
the leafl injury from either. 
4. Even while faturated with water in their porous {late, 
they may be thrown immediately into a white heat, without 
burfling or fuffering any injury. 
5. Sudden cooling, which alters both the bulk and texture 
of mofl bodies, does not at all affedl thefe, at leafl not in 
any quality fubfervient to their thermometric ufes. 
6. Nor are they affedted by long continuance in, but folely by,, 
the degree of heat they are expofed to. In three minutes or 
lefs, they are perfedlly penetrated by the heat which a£ts upon 
them, fo as to receive the full contraction which that degree 
of heat is capable of producing equally with thofe which had 
undergone its aCtion during a gradual increafe of its force for 
many hours. Strong degrees of heat are communicated to 
them with more celerity than weak ones : perhaps the heat 
may be more readily tranfmitted, in proportion as the texture 
becomes more compaCl. 
Thefe faCls have been afcertained by many experiments, the 
particulars of which are omitted, becaufe they would fwelL 
this paper much beyond the bulk intended. 
XI. The 
