nettle hard, in order to pull it out: but this fact another season will clear up. It would be curious indeed, if the nettle should be found to instil its poison into the wound it makes, by a power it may deprived of by squeezing it hard.

be

I have now troubled you, my Lord, too long, and I am afraid to little purpose. Whether you may discover the traces of mechanism, or ascribe these phenomena to some unknown principles, I am sure it would give me very great pleasure to learn from you what I am to think of the matter.

I shall most certainly take the first opportunity I can find, either at Edinburgh or in the country, to wait upon your Lordship, and to pay my respects to the botanic Lady who threatens me with a visit. She shall certainly find me more complaisant than Mahomet did the mountain; though I believe the best way to ensure the visit she promises, would be to keep out of her sight till she sees me here.— With respectful compliments to her, I am, with entire esteem and regard, your Lordship's, &c.

J. NASMITH.

Here is a bit of more paper, and therefore I will add, that they have got of late into some of the gardens, a new species of the sensitive plant, that is so very feeling, that if a fly pitches upon a leaf, it closes so suddenly, and with so much force, as to catch and crush the insect to death.

IV.

IV. From Dr THOMAS REID to Lord KAMES.

On some Doctrines of Dr Priestley; and of the French Philosophers.

1775.

Dr Priestley, in his last book, thinks, that the power of perception, as well as all the other powers that are termed mental, is the result of such an organical structure as that of the brain. Consequently, says he, the whole man becomes extinct at death, and we have no hope of surviving the grave, but what is derived from the light of Revelation. I would be glad to know your Lordship's opinion, whether, when my brain has lost its original structure, and when, some hundred years after, the same materials are again fabricated so curiously as to become an intelligent being, whether, I say, that being will be me; or, if two or three such beings should be formed out of my brain, whether they will all be me, and consequently all be one and the same intelligent being.

This seems to me a great mystery, but Priestley denies all mysteteries. He thinks, and rejoices in thinking so, that plants have some degree of sensation. As to the lower animals, they differ from us in degree only, and not in kind. Only they have no promise of a resurrection. If this be true, why should not the King's Advocate be ordered to prosecute criminal Brutes, and you Criminal Judges to try them. You are obliged to Dr Priestley for teaching you onehalf of your duty, of which you knew nothing before. But I forgot

that

that the fault lies in the Legislature, which has not given you laws I hope, however, when any of them shall be

for this purpose.
brought to a trial, that he will be allowed a jury of his peers.

I am not much surprised, that your Lordship has found little entertainment in a late French writer on Human Nature*. From what I learn, they are all become rank Epicureans. One would think, that French politesse might consort very well with disinterested benevolence; but, if we believe themselves, it is all grimace. It is flattery, in order to be flattered; like that of the horse, who when his neck itches, scratches his neighbour, that he may be scratched by him again. I detest all systems that depreciate human nature. If it be a delusion, that there is something in the constitution of man that is venerable, and worthy of its Author, let me live and die in that delusion, rather than have my eyes opened to see my species in a humiliating and disgusting light. Every good man feels his indignation rise against those who disparage his kindred or his country; why should it not rise against those who disparage his kind? Were it not that we sometimes see extremes meet, I should think it very strange to see atheists and high-shod divines, contending as it were who should most blacken and degrade human nature. Yet I think the atheist acts the more consistent part of the two: for surely such views of human nature tend more to promote atheism, than to promote religion and virtue.

* HELVETIUS, De PEsprit.

V.

V. FROM THE SAME.

On the Conversion of Clay into Vegetable Mould.

October 1. 1775.

The theory of agriculture is a wide and deep ocean,

wherein we soon go beyond our depth.

I believe a lump of dry clay has much the same degree of hardness, whether the weather be hot or cold. It seems to be more affected by moisture or drought: and to be harder in dry weather, and more easily broken when a little moistened. But there is a degree of wetness in clay which makes it not break at all when struck or pressed it is compressed and changes its figure, but does not break.

Clay ground, I think, ought to be ploughed in the middle state, between wetness and dryness, for this reason: When too dry, the plough cannot enter, or cannot make handsome work. Those clods are torn up, which require great labour and expence to break them. And unless they are broken, the roots of vegetables cannot enter into them. When too wet, the furrow, in being raised and laid over by the plough, is very much compressed, but not broken. The compression makes it much harder when it dries, than it would have been without that compression. But when the ground is neither too wet, nor too dry, the furrow, in being raised and laid over by the plough, breaks or cracks with innumerable crevices, which admit air and moisture, and the roots of vegetables.

Clay,

Clay, when exposed in small parts to the air, and to alternate moisture and drought, mellows into mould. Thus a clod of clay, which is so hard in seed-time, that you may stand upon it without breaking it, will be found in autumn of the colour of mould, and so softened, that when you press it with the foot it crumbles to pieces. On some clays this change is produced in a shorter time, in the same circumstances; others are more refractory, and require more time.

If wet clay is put into the fire uncompressed, I am informed that it burns to ashes, which make no bad manure.

But if the clay be wrought and compressed when wet, and then dried, and then put into the fire, it burns into brick, and with a greater degree of heat, into a kind of glass.

These, my Lord, are facts; but to deduce them from principles of attraction and repulsion, is beyond the reach of my philosophy: and I suspect there are many things in agriculture, and many things in chemistry, that cannot be reduced to such principles; though Sir Isaac Newton seems to have thought otherwise.

Human knowledge is like the steps of a ladder. The first step consists of particular truths, discovered by observation or experiment: The second collects these into more general truths: The third into still more general. But there are many such steps before we come to the top; that is, to the most general truths. Ambitious of knowledge, and unconscious of our own weakness, we would fain jump at once, from the lowest step to the highest. But the consequence of this is, that we tumble down, and find that our labour must be begun anew. Is not this a good picture of a philosopher, my Lord? I think so truly; and I should be vain of it, if I were not afraid that I have stolen it from Lord Bacon. I am, &c.

THO. REID.