[_The lamps nocturnal_. l. 189. The ignis fatuus or Jack a lantern,
frequently alluded to by poets, is supposed to originate from the
inflammable air, or Hydrogene, given up from morasses; which being of a
heavier kind from its impurity than that obtained from iron and water,
hovers near the surface of the earth, and uniting with common air gives
out light by its slow ignition. Perhaps such lights have no existence,
and the reflection of a star on watery ground may have deceived the
travellers, who have been said to be bewildered by them? if the fact was
established it would much contribute to explain the phenomena of
northern lights. I have travelled much in the night, in all seasons of
the year, and over all kinds of soil, but never saw one of these Will
o'wisps.]

[_Shine round Calendula_. l. 191. See note on Tropaeolum in Vol. II.]

[_The radiant Worm_. l. 193. See additional notes, No. IX.]

[_The dread Gymnotus_. l. 202. The Gymnotus electricus is a native of
the river of Surinam in South America; those which were brought over to
England about eight years ago were about three or four feet long, and
gave an electric shock (as I experienced) by putting one finger on the
back near its head, and another of the opposite hand into the water near
its tail. In their native country they are said to exceed twenty feet in
length, and kill any man who approaches them in an hostile manner. It is
not only to escape its enemies that this surprizing power of the fish is
used, but also to take its prey; which it does by benumbing them and
then devouring them before they have time to recover, or by perfectly
killing them; for the quantity of the power seemed to be determined by
the will or anger of the animal; as it sometimes struck a fish twice
before it was sufficiently benumbed to be easily swallowed.