of troops, as soon as evening came on, if I had occasion to go into a dark room, the whole scene was brought before my eyes, with a brilliancy equal to what it had possessed in day-light, and remained visible for several minutes. I have no doubt, that dismal and frightful images have been presented, in the same manner, to young persons, after scenes of domestic affliction, or public horror.

From this renewal of external impressions, also, many of the phænomena of dreams admit an easy explanation. When an object is presented to the mind, during sleep, while the operations of judgment are suspended, the imagination is busily employed in forming a story, to account for the appearance, whether agreeable or distressing. Then the author enjoys the delight of perusing works of infinite wit and elegance, which never had any real existence, and of which, to his utter mortification, he cannot recollect a single line, next

morning; and then the Bibliomane purchases illuminated manuscripts, and early editions on vellum, for sums so trifling, that he cannot conceal his joy from the imaginary vender.

Dr. R. Darwin seems to believe, that it is from habit only, and want of attention, that we do not see the remains of former impressions, or the muscæ volitantes, on all objects.* Probably, this is an instance, in which the error of external sensation is corrected by experience, like the deceptions of perspective, which are undoubtedly strong in our childhood, and are only detected by repeated observation.

"After having looked," says Dr. Dar"win, "long at the meridian sun, in

making some of the preceding experi "ments, till the disk faded into a pale “blue, I frequently observed a bright "blue spectrum of the sun in other

*Zoonomia, Sect. xi, 2.

266

objects all the next and the succeeding day, which constantly occurred when “I attended to it, and frequently when "I did not attend to it. When I closed "and covered my eyes, this appeared "of a dull yellow; and at other times "mixed with the colours of other objects on which it was thrown."*

It is scarcely necessary to mention the well-known experiment of giving a rotatory motion to a piece of burning wood, the effect of which is to exhibit a complete fiery circle to the eye.

To this principle of a renewal of impressions formerly made by different objects, belongs the idle amusement of tracing landscapes, and pictures of various composition, in the discoloured spots of an old wall. This may be truly calleda waking dream, as it is composed of the shreds and patches of past sensations; yet there are, perhaps, few persons who.

* Sect. xi. 8.

have not occasionally derived entertainment from it. It is probably on the same principle, that we are to account for the appearances of armies marching, in desart and inaccessible places, which are sometimes beheld by the inhabitants of the vallies, in mountainous regions. The accidents of light and shade, and the interposition of partial fogs, or clouds, produce the same effect on the eye, as the discoloured patches of the wall; and the rolling of the mist adds motion to the spectral images.

In like manner, recollected images are attributed to the moving lights, in the splendid exhibitions of the Aurora Borealis. The Icelander beholds in them the spirits of his ancestors; and the vulgar discern encountering armies, and torrents of blood, in the lambent meteors of a winter-sky. The humble diversion of seeing pictures in the fire, which

* Voyage d' Islande, in the Ambigu.

occupies children of smaller growth in the nursery, is calculated on the same principles. In some cases, the imagination is assisted by physical causes, in a very imposing manner, as in the instance of the Giant of the Broken,* in Ger

* I subjoin the original account, as it will amuse the reader.

"In the course of my repeated tours through the Harz,* I ascended the Broken twelve times; but I had the good fortune only twice, (both times about Whitsuntide) to see that atmospheric phonomenon, called the Spectre of the Broken, which appears to me worthy of particular attention, as it must, no doubt, be observed on other high mountains, which have a situation favorable for producing it. The first time I was deceived by this extraordinary phenomenon, I had clambered up to the summit of the Broken very early in the morning, in order to wait for the inexpressibly beautiful view of the sun rising in the east. The heavens were already streaked with red; the sun was just appearing above the horizon in full majesty, and the most perfect serenity prevailed throughout the surrounding country, when the other Harz mountains in the south west, towards the Worm mountains, &c. lying under the Broken began to be

*The Harz mountains are situated in Hanover.

B