leaves. The Senfitiva Mimofa, and Mufcipula Dionea, fhew wonderful activity on the flightest impreffions, and take the flies and other infects prifoners, by the contraction of their leaves. That these plants live, will be granted; but I fufpect, that they likewife feel. I doubt whether we are right, in confining the capacity of pleasure and pain to the animal kingdom. This I may affirm, that fome circumftances, common to the generation of plants and animals, and many fimilarities in their functions and ftructure, would lead us to the opinion, that fenfation likewife is bestowed on both.* It is vain to attempt to establish abfolute rules, by which plants may be distinguished from animals, in every cafe whatsoever. There are animals, which grow to a spot, and, like plants, are nourished by the pores of the skin. And there are plants, which surpass some animals in vital power, and, perhaps, in fenfation.

Wherever the principle of life exifts, there is a peculiar organization; and as much mechanifm is neceffary to the structure of a vegetable, as of a human being. This view of the life of vegetables raises botany to the rank of philofophy:

The excellent profeffor of botany in Edinburgh, Dr. Hope, in his course of lectures, used to speak of Dr. Bell with the highest efteem: but did not approve of the idea here thrown out, that plants poffefs feeling, or perception. J. C.

it adds fresh beauty to the parterre, and gives new dignity to the foreft.

It only remains, that I excufe myself for writing on a botanical fubject, when I am a candidate for medical honours. A few words will fuffice. Such is the analogy between vegetables and animals, that the knowledge of the nature of the one illuftrates that of the other and as vegetables, in every part of the world, form a great part of our food, as well as of our medicines, it is highly important for every physician to be well acquainted with their nature.

Some OBSERVATIONS on the PHENOMENA, which take PLACE between OIL and WATER, in a LETTER to THOMAS PERCIVAL, M.D. F.R.S. and S. A. &c. By MARTIN WALL, M. D. Prælector of Chemistry in the University of Oxford. Read Nov. 17, 1784.

DEAR SIR,

TH

HE action of bodies on each other, the principles upon which that action depends, and the causes, which under certain circumftances diminish, impede, or prevent it, have defervedly

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defervedly occupied no fmall fhare of the attention of philofophers; because on the knowledge of thefe principles, depend, not merely a curious science, but very many of the neceffary arts of life. In the earliest periods of philofophy, little progrefs was made in this investigation. Some crude conjectures were advanced concerning peculiar emanations, &c. which, having no foundation in experiment, were as quickly rejected as they had been formed. The patrons of the corpufcular philofophy imputed the influence of bodies on each other, or the defect of fuch influence, to the peculiar forms of their original particles; and the mechanic fect fuperadded to this fyftem the doctrine of attraction. The theory which depends upon the form of the conftituent particles of bodies, is very weak and unfatisfactory, and, if it has not been abfolutely confuted by experiments, has certainly received no confirmation from them. But the grand principle of attraction, has, by the clearest evidence of conclufive facts, received the most ample confirmation, its laws have been explained, and the univerfal extent of its operation has been fo fully demonftrated, that Bergman was perfectly justified in speaking of it, as the principal agent in every operation, grand or minute, in the fyftem of the world," cui omnia in globo noftro obedire videntur."

The

The action, however, of this great agent is not fimple and uniform: it admits of great yariation, and operates by different laws, as we fee in the different phænomena of gravitation, of cohesion, of electricity, of magnetifm, and of chemical affinity. Thus, in our electrical and magnetical experiments, we have frequent occafion to observe, that the fame bodies which are attracted by one are repelled by a third, and inter fe, as as the circumstances of the experiment are varied. Perhaps, fomething of the fame kind may limit or impede the attraction of gravitation and cohefion, in particular cafes. Hence philofophers have fuppofed another principle of nature, oppofite to that of attraction, which they have denominated repulfion, and have imagined the influence of this principle to begin, where that of attraction ends. The obfervations deduced from the phænomena above alluded to, have been transferred alfo to chemistry; and because certain bodies fhew no difpofition to form a chemical union, they have been faid to poffefs a repulfive faculty with respect to each other. To fay, that a principle of repulfion has no exiftence in nature, would be too prefumptuous: but I am inclined to believe, that the fpecies of attraction, which conftitutes chemical affinity, is not counteracted by any principle of repulfion in thofe cafes, where no affinity appears to take place; and that the apparent repulfion

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repulfion depends upon a perfectly different cause. To pursue this doctrine through all those inftances of chemical fubjects, which fhew no difpofition to unite, would be almost endless; but that I may give it a little illuftration, permit me to draw your attention to one example.

One of the most common examples adduced of this repulfion, is, the immifcibility of oil with water, which cannot be effected without fome intermedium. But what is here called repulfion, is perhaps, only a cafe of that kind which is called elective attraction (if I may be allowed to adopt that expreffion) that is, that the particles of water attract those of water, and the particles of oil thofe of oil, more strongly than oil attracts water; and, therefore, when thefe are mixed or brought into contact, no new or more powerful attraction taking place, both ingredients continue diftinct and difunited: and it is upon the fame account, that when one of these fluids is inveloped in the other, it is difpofed to form itself into one or more fpherules from the strong attraction of its particles inter fe.

The principle thus laid down will receive illuftration from, and at the fame time will aflift to explain, fome phænomena refulting from the immifcibility of oil and water, which, though well known, have not been much regarded in a philofophical point of view. The facts, to which I particularly allude, are, the effect of