are infenfible to the greateft changes in the circumambient heat. Moft of the discous flowers, obedient to the impulfe of light, follow the fun in his courfe. They attend him in his evening retreat, and meet his rifing luftre in the morning. If a plant be fhut up in a dark room, and a small hole be made in the fhutter, through which the light may penetrate, you would fee the different plants confined there, turn towards that hole, and even alter their shape to creep through it, so that though thefe were ftraight before, they would in a fhort time. become crooked, to obtain the full enjoyment of light. Thus if a GERANIUM be placed in any window for a certain time, the interior furface of every leaf would be turned to meet the light; and if you remove it to an oppofite window, you would foon fee a fad contortion and confufion among the leaves, until they had obtained a right position with regard to light. To prove that it is not heat, but light, which plants covet, if this GERANIUM be placed near a fire, which gives a stronger heat than the fun, you would foon obferve it turn away its leaves and flowers from the fire to the fun.

To illuftrate this curious circumftance, Dr. HILL placed a plant of abrus in a room, where it had moderate day-light, without the fun fhining upon it. The lobes

of the leaves were then fallen perpendicularly from the middle rib, and clofed together by their under fides. Thus they continued all night. Half an hour after daybreak, they began to separate, and a quarter of an hour after fun-rife, were perfectly expanded. Long before fun-set they began to droop again, and towards evening were closed as at first.

Next day the plant was placed where there was lefs light. The lobes were raised in the morning, but not fo much and they drooped earlier at evening.

The third day it was fet in a fouth window, open to the full fun.-Early in the morning the leaves had attained their horizontal fituation: by nine o'clock they were raised above it, and continued fo till late in the evening; then they fell to the horizontal fituation, and thence gradually to the usual state of rest.

Thefe experiments prove that the whole change is occafioned by light only. To put this beyond dispute, in the evening of the fixth day, the plant was fet in a book-cafe, on which the morning fun fhone, the doors ftanding open. The day was bright. The lobes, which had closed in the evening, began to open early in the morning, and by nine o'clock, they were raised in the ufual manner. I then, fays he, hut the doors of

the

the book-cafe: on opening them an hour after, the lobes were all clofed as at midnight. On opening the door they expanded again, and in twenty minutes they were

fully expanded. This has fince been many times reWe can

1

peated, and always with the fame fuccefs.

therefore, by admitting or excluding the light, make the plant put on all its changes. Hence we are certain, that what is called the fleep of plants, is caused by the abfence of light alone, and that their various intermediate ftates are owing to its different degrees.

Some experiments on plants give us reason to believe, that light combines with certain parts of vegetables, and that the green of their leaves, and the various colours of their flowers, is chiefly owing to this combination. This much is certain, that plants which grow in darkness are perfectly white, languid, and unhealthy, and that to make them recover vigour, and to acquire their natural colour, the direct influence of light is abfolutely neceffary.

It would be difficult, in the present state of chemical knowledge, to fhew the combination of light with our bodies. But it cannot but be allowed, that light is a stimulus, awaking us to muscular action, and opening an

inlet

*, and

more

inlet to the ftimulus of the various paffions *, efpecially to the powerful influence of fight. The boy, who was couched for blindnefs by Mr. CHESElden, had no great expectation of pleasure from a new sense; he was only excited by the hopes of being able to read and write; he said, for instance, that he could have no greater pleasure in walking in the garden with his fight, than he had without it, for he walked there at his ease, and was acquainted with every turn. He remarked alfo, with great juftice, that his former blindness gave him one advantage over the rest of mankind, which was that of being able to walk in the night, with confidence and fecurity. But, when he began to make use of this new fenfe, hé feemed transported beyond measure. The

* A thick and impenetrable cloud of darkness on a fudden enveloped the Grecian army, and fufpended the battle. AJAX, perplexed what course to take, prays thus,

Accept a warrior's pray'r, eternal Jove;

This cloud of darkness from the Greeks remove,

Give us but light, and let us fee our foes,

We'll bravely fall, tho' Jove himself oppose.

The fentiments of AJAX are here pathetically expreffed: it is AJAX himself. He begs not for life: a request like that would be beneath a hero. But because in that darkness he could difplay his valour in no illuftrious exploit, and his great heart was unable to brook a sluggish inactivity in the field of action, he only prays for light, not doubting to crown his fall with fome notable performance, though Jove himself should oppofe his efforts. LONGINUS.

brightness

brightnefs of the day, the azure vault of heaven, the verdure of the earth, the crystal of the waters, all employed him at once, and animated and filled him with inexpreffible delight. He turned his eyes towards the fun. Its fplendour dazzled and overpowered him he fhut them once more; and, to his great concern, he fuppofed that, during this fhort interval of darkness, he was returning to nothing. New ideas now began to arife; new paffions, as yet unperceived, with fears, and pleasures, all took poffeffion of his mind, and prompted his curiofity: love ferved to complete his happiness; and every fenfe was gratified in all its variety.

I had not, perhaps, been thus diffufe on the article of light, unless I had obferved, that all animals, when afflicted with illness, fly inftinctively to fome filent and dark retreat, where, unaided by art, they quickly recover; and that man, left to the guidance of reason only, often falls fhort in this respect of the brute creation, and frequently his powers, already weakened by difeafe, get ftill the more exbaufted by an imprudent admiffion of company and light.