I would rather make use of
_them_ to praise Mr. Jenkins's general kindness and hospitality to all
his country-folks, who find a certain friend in him; and if they please,
a very competent instructor.

In order however to understand the meaning of some spherical _pots_
observed in the Circus of Caracalla, I chose above all men to consult
Mr. Greatheed, whose correct taste, deep research, and knowledge of
architecture, led me to prefer his account to every other, of their use
and necessity: it shall be given in his own words, which I am proud of
his permission to copy.

"Of those _pots_ you mention, there are not any remaining in the Circus
Maxiouis, as the walls, seats and apodium of that have entirely
disappeared. They are to be seen in the Circus of Caracalla, on the
Appian way; of this, and of this alone, enough still exists to ascertain
the form, structure, and parts of a Roman course. It was surrounded by
two parallel walls which supported the seats of the spectators. The
exterior wall rose to the summit of the gallery; the interior one
was much lower, terminated with the lowest rows, and formed
the apodium. This rough section may serve to elucidate my
description. From wall to wall an arch was turned which formed a
quadrant, and on this the seats immediately rested: but as the upper
rows were considerably distant from the crown of the arch, it was
necessary to fill the intermediate space with materials sufficiently
strong to support the upper stone benches and the multitude. Had these
been of solid substance, they would have pressed prodigious and
disproportionate weight on the summit of the arch, a place least able to
endure it from its horizontal position. To remedy this defect, the
architect caused _spherical pots_ to be baked; of these each formed of
itself an arch sufficiently powerful to sustain its share of the
incumbent weight, and the whole was rendered much less ponderous by the
innumerable vacuities.

[Illustration]

"A similiar expedient was likewise used to diminish the pressure of
their domes, by employing the scoriae of lava brought for that purpose
from the Lipari Islands. The numberless bubbles of this volcanic
substance give it the appearance of a honeycomb, and answer the same
purpose as the pots in Caracalla's Circus, so much so, that though very
hard, it is of less specific gravity than wood, and consequently floats
in water."

Before I quit the Circus of Caracalla, I must not forbear me