summers, must certainly leave a mud of the same kind and quality.

'Putrid juices and putrid vapours are dispersed through the earth and air, so that there are few earths of an absorbent kind that are not, in some degree, nitrous.

P. 197. Glauber, who, from the observations he had made upon the fruits and effects of the bottoms of stinking ditches, seems to be the first that attempted to form artificial nitre beds, threw into pits, covered from the rain and sun, but exposed as much as possible to the air, all sorts of dung, with the cuttings of trees, refuse of gardens, and other putrid and putrefiable matters, to which he added woodashes; and, by this means, in a course of time, obtained, not a mere nitrous, but a true saltpetre earth, that afforded him the crystals of this salt upon simple elixiviation and evaporation.

'It does not appear that this celebrated chemist had the least idea that these putrid matters were of any other use than to draw the nitre, as he called it, from the air, in which the fixed salt of the wood-ashes might possibly assist.'

P. 201. 'About thirty years ago, an ingenious chemist of our own nation, having visited many of the great works abroad, and made the observation, that to form a nitrous earth nothing more appeared to be necessary than to mix up calcareous earths with any kind of dung, and expose these materials to the air, returned home, fully persuaded that he was master of the secret, and had interest enough to prevail upon many of his friends to join him in erecting a large saltpetre works, at Fulham, near London. Here many

hundred loads of lime were got together, and laid, with strata of horse muck, in long high ridges, the more to be exposed to this element; the consequence of which was, that the rain running off, without penetrating the mass, no putrefaction ensued, and the lime, at the end of four or five years, was found to have received little or no impregnation ; upon which the work was dropped, with great loss to the proprietors.'

P. 211. Upon many accounts it has been before observed that Glauber sometimes threw all sorts of dung into a large wooden vessel, and, when they had completed their putrefaction, percolated a fixed alkaline solution through them; which furnished him with a ley of the same kind and nature with that drawn from nitrous earths and woodashes.'

P. 220. All these things being considered, with the practice of the Swedes, and the success of our own experiments, we judge ourselves authorised to advise all those who are employed in making saltpetre, to place but a few wood-ashes at the bottom of their tubs, to serve by way of filter, and to supply their place with potash.

CHAPTER VIII.

ESSAYS AND LIVES, VOLS. I.-IV.

Sensation and Perception in Vegetables.

DR. PERCIVAL wrote a short essay on the perceptive powers of vegetables, called by himself, partly in excuse for thinking in such a manner, a jeu d'esprit; he seems to have felt uncertain whether he would print it or not. Some parts of this paper raise the author high as a general thinker on nature, and show that he had talents for investigation, and certainly for an observer, although his gentle nature and want of bodily strength led him into calmness of thought, which frequently produces diffuseness of style. Still he who looks on nature with the eye of a poet and a moralist, with much knowledge of natural law, and much acquaintance with phenomena, is a man of a high class, and in some respects of a much higher class than the man of genius, who sees in one direction only, although he who sees far is the rare man, and one to whom humanity owes most and gives most honour, and to whom alone we are accustomed to apply the title of Great.

To the first class of men Dr. Percival certainly belonged, seeing nature in its great width and watching the existence of mind, descending even to the plants as life itself does.

Some may say that the fundamental idea in the paper shows a touch of genius, and to this we might have agreed had we not known that it has occurred to many young sympathetic minds. Several have tried to give it a place in scientific thought. We remember it as a natural outgrowth of our childhood, when untaught by any one we stopped the process of cutting a branch lest perhaps it felt pain, an idea nourished in us afterwards by Virgil, who learnt it from a long line of literary ancestors by fairy tales. from various nations, including ancient Egypt; but many ideas require no ancestors except the germs existing not solely as bodies, but as the peculiar movements of bodies in human blood,

As we write this we think of sacred trees, and bleeding bushes, trees in which lived Hamadryads, or trees which live and die with chosen individuals. The whole world has been given a soul as early as Plato, and Pantheism puts this soul everywhere; but to approach it as a naturalist shows a change of aspect of the question and a certain amount of boldness if Dr. Percival really did approach it of his own impulse; had he read Adamson for example? It would appear as if he had not, and he seems not to have read Dr. George Bell's essay, which however was printed afterwards in the same volume. We shall bring an extract from it before Percival's paper.

Dr. Bell's article 'On the Physiology of Plants,' vol. ii. P. 394, was written previous to Percival's, and published in Edinburgh 1777, as a Latin thesis. It was translated by Dr. Currie and published in these Memoirs; he says

'The analogy between vegetables and animals, which was formerly pointed out, gives a reasonable presumption

that the fluids of both are moved by similar powers. In animals, the powers of circulation are respiration and muscular action; of those powers in plants we have already treated, and what has been said on the subject seems to show, that the motion of the juices in plants is rather to be ascribed to them than to capillary attraction.

'The analogy of animal nature appears to favour the opinion, that the juice rises through the wood only, and descends only through the bark; but this analogy is not complete throughout. The arteries are not placed in the internal parts alone, nor the veins in the external, but they accompany each other through every part of their distribu

tion.

'On the whole we may conclude, that the formation and growth of the parts of plants depend chiefly on the vital energy, which is not however exerted except on the application of stimuli. We admire the marks of wisdom and design, which appear in the creation and preservation of vegetables, but we have no reason to believe that they are possessed of any intelligent power, which presides over and directs their peculiar functions.

'The principle of life seems universally diffused through nature, but bestowed on different beings in different degrees. To animals is given the largest share; but throughout the whole animal kingdom, one species descends below another in the perfection of its mental powers, as well as of its organic sensations. And this progression is so very gradual, that the most perfect of an inferior species approaches very near to the most imperfect of that which is above it. The chain is continued between vegetables and animals.

'And if we admit such motions, as criteria of a like power