The Bolognian stone is a selenite, or gypsum, and has been long celebrated for its phosphorescent quality after having been burnt in a sulphurous fire; and exposed when cold to the sun's light. It may be thus well imitated: Calcine oyster-shells half an hour, pulverize them when cold, and add one third part of flowers of sulphur, press them close into a small crucible, and calcine them for an hour or longer, and keep the powder in a phial close stopped. A part of this powder is to be exposed for a minute or two to the sunbeams, and then brought into a dark room. The calcined Bolognian stone becomes a calcareous hepar of sulphur; but the calcined shells, as they contain the animal acid, may also contain some of the phosphorus of Kunkel.] [_In Memnon's fane_. l. 183. See additional notes. No. VIII.] "YOU with light Gas the lamps nocturnal feed, 190 Which dance and glimmer o'er the marshy mead; Shine round Calendula at twilight hours, And tip with silver all her saffron flowers; Warm on her mossy couch the radiant Worm, Guard from cold dews her love-illumin'd form, 195 From leaf to leaf conduct the virgin light, Star of the earth, and diamond of the night. You bid in air the tropic Beetle burn, And fill with golden flame his winged urn; Or gild the surge with insect-sparks, that swarm 200 Round the bright oar, the kindling prow alarm; Or arm in waves, electric in his ire, The dread Gymnotus with ethereal fire.-- Onward his course with waving tail he helms, And mimic lightenings scare the watery realms, 205 So, when with bristling plumes the Bird of JOVE Vindictive leaves the argent fields above, Borne on broad wings the guilty world he awes, And grasps the lightening in his shining claws. [_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.]