the atmosphere. A number of observations on the duration of twilight in
different latitudes might afford considerable information concerning the
aerial strata in the higher regions of the atmosphere, and might assist
in determining whether an exterior atmosphere of inflammable gas, or
Hydrogene, exists over the aerial one.]

[_Alarm with Comet-blaze_. l. 133. See additional notes, No. IV.]

[_The Sun's phlogistic orb_. l. 136. See additional notes, No. V.]


III. NYMPHS! YOUR fine forms with steps impassive mock
Earth's vaulted roofs of adamantine rock;
Round her still centre tread the burning soil,
140 And watch the billowy Lavas, as they boil;
Where, in basaltic caves imprison'd deep,
Reluctant fires in dread suspension sleep;
Or sphere on sphere in widening waves expand,
And glad with genial warmth the incumbent land.
145 So when the Mother-bird selects their food
With curious bill, and feeds her callow brood;
Warmth from her tender heart eternal springs,
And pleased she clasps them with extended wings.


[_Round the still centre_. l. 139. Many philosophers have believed that
the central parts of the earth consist of a fluid mass of burning lava,
which they have called a subterraneous sun; and have supposed, that it
contributes to the production of metals, and to the growth of
vegetables. See additional notes, No. VI.]