An EXPLANATION of the SIXTH PLATE
A Piece of Kettering-Stone
THIS Stone, which has a very extraordinary Grain, much different from all other
Kinds of Stone, is dug from a Quarry at Kettering in Northamptonsbire. It ap-
peared through the Microscope made up of numberless little Pebbles, whose Figure was
nearly globular, though they were not all exactly of the same Shape or Bigness some ex-
ceeding others three or four times in Diameter. They seemed, to the naked Eye, like
the Ovary or Hard-Row of an Herring, or some smaller Fish; but the little Grains were
neither so large nor so uniform. Their Variation in Shape from perfect Roundness looked
as if occasioned entirely by the Pressure of some of the Balls against others, whereby the
Sides where the Pressure took place, became a little depressed inwards, and the other Parts
became protruded proportionably outwards, beyond the Limits of a Globe; in the same
manner as it would happen, if an Heap of exactly round Balls of soft Clay were piled
upon one another.
These Grains were so firmly united together where they touch each other, that they
seldom could be parted without breaking an Hole in one or both; which Fractures are
shewn by a, a, a, b, c c, &c.
In several, where the Pressure had been but light, no more was broken than the out-
ward Crust or Shell of the Stone, which appeared of a white Colour, dash'd a little with
a brownish yellow, and very thin like the Shell of an Egg. Nay, some of those Grains
were found perfectly to resemble Eggs both in Colour and Shape. But where the Union
of the contiguous Grains was more firm, the Divulsion there occasioned a larger Chasm,
as at b, b, b.
Some were also observed broken quite in two, and discovered by two different Sub-
stances, encompassing each other in the Manner of a White and Yolk, a nearer Refem-
blance still to Eggs, as c, c, c.
What we term the White, was pretty whitish near the Yolk, but grew more dusky
towards the Shell, and in some was radiated like a Pyrites. The yolk-like Part was hol-
low in some, but filled in others with a darkish brown and porous Substance, like a Kind
of Pitch, as at d.
The Interstices or small Pores between the Globules, e, e, e, e, were found, b several
Experiments, to be pervions every Way both to Air and Water ; for on blowing through
a Piece of this Stone of a considerable Thickness, the Air passed as easily as through a
Cane : And when another pretty large Piece was covered all over with Cement, except at
the two opposite Ends, by blowing in at one End, some Spittle wherewith the other was
wetted, was raised into Abundance of Bubbles, and served to prove how porous some Bo-
cies are which appear seemingly compact and close.
The Microscope discovers here a Stone, composed of innumerable minute Balls, which
merely touch each other, and yet by so many Contacts constitute a Substance much harder
The Interstices between these Balls must render it very useful, when formed into proper
Vessels, for the Filtration of Water or any other Liquors.
PLATE VI. FIG. 2.
THIS Picture represents a Kind of Sea-Plant or Fucus, called by Mr. RAY, in his
Synopsis, Fucus telam lineam sericeamve texturâ suâ æmulans. It grows on the
Rocks under Water, and spreads out into a great Tuft, which branches into several
Leaves of a most beautiful and surprising Structure. But of this we shall defer giving
any farther Deseription, till we come to the first Figure of the Eleventh Plate.
PLATE VI. FIG. 3.
A Piece of Spunge
THE Texture of this Object is discovered by the Microscope to consist of innume-
rable, small, short, round Fibres, nearly of the same Bigness, jointed very curi-
ously together in a Kind of Net-like Form. The Joints are most commonly where only