the Thermometer for high Degrees of Heat . 393 
flrong fires, to differ in their dimenfions from one another, in- 
fame i'nftanees more than any of the preceding. 
Having hitherto paid no particular attention myfelf to the 
mere manual labour of prefling the clay,, I determined, upon- 
this event, to go through that and every other operation, how- 
ever Ample and feemingly infignifieant, with my own hands. 
In doing this 1 obferved, that the power neceflary for forcing 
the clay through an aperture which bore but a fmall propor- 
tion to the diameter of the mafs of clay in the prefs, was (b 
great as to fqueeze out, along with the clay that firft paffed 
through, a confiderable portion of the water that belonged to 
the reft. From this over-proportion of water in the compofi- 
tion of the firft pieces they were foft and fpongy, and the fuc- 
ceeding ones more and more compact, till at length the clay 
proved fo ftifF as fcarcely to be forced through at all. 
Clay, containing different proportions of water, is well 
known to diminifh differently in drying ; but it was not ima- 
gined that, when dry, there would be any difference in its 
fubfequent diminutions by fire. Experiments however, multi- 
plied in a variety of circumftances, (hewed decifively, what 
the pieces formed in the mould had given grounds to fufpe&y 
that thofe formed of the fofteft clay, and which had under- 
gone the lead prefliire, diminiftied mod in burning ; and that 
the diminution is uniformly lefs and lefs, in proportion to the 
greater degree of prefliire or compacftiefs* 
The knowledge of the caufe of the irregularity fuggefted a 
remedy. J leflened the width of the prefs very much, fo as to 
bring the diameter of the mafs of clay, and that of the aper- 
ture through which it is delivered, to a nearer proportion, with, 
one another. A much lefs degree of force being now diffi- 
dent,. the pieces, or rods, were proportionably more uniform,, 
though 
