It appears to me that it is of much greater consequence to disprove these statements, than to dispute about their origin. I shall, therefore, in the first place, examine the statements relating to the structure of the spinal marrow, and shall then produce some objections relative to the functions of the cerebellum as stated by Willis and by Mr. A. Walker.

It is said that the spinal marrow is composed of four longitudinal divisions, two larger, anterior, which may be traced into the cerebrum; and two smaller, posterior, which may be traced into the cerebellum. This statement is erroneous in two respects: 1. There are not four divisions; there exist only two fissures, one at the anterior part of the spinal marrow, the other at the hinder part; but there are no lateral fissures. Such are the statements of Gall and Spurzheim; and my recent examinations have convinced me of their truth. Gall and Spurzheim have shown that the spinal mass of nerves is composed of a series of as many swellings as there are hairs of nerves, and they have pointed out that the anterior fissure* is less deep than the posterior, and that the posterior nerves are more considerable than the anterior. It is, therefore, erroneous to say that of the four divisions the anterior are larger, and the posterior smaller.

Mr. A. Walker considers the anterior fasciculi as ascending, and the two posterior as descending. Gall and Spurzheim have shown that the brain and cerebellum cannot be considered as the continuation of the spinal marrow, any more than the spinal marrow can that of the brain and cerebellum. There are examples of monstrous foetuses having only the lower parts of the spinal marrow, and yet the posterior and anterior (or, according to Mr. A. Walker, the ascending and descending,) fasciculi have been found to exist. It. is, therefore, evident, that they cannot be considered as descending from the cerebellum. Gall and Spurzheim have also shown that not only the cerebellum, but also the hinder parts of the brain, are brought in communication with posterior parts of the spinal mass of nerves, and that only a small fasciculus of the hinder part of the spinal mass of nerves belongs to the cerebellum.

The physiological statements of Mr. A. Walker are not more accurate than his anatomical ones; they are merely suppositions, and at variance with nature. The cerebellum he considers as the organ of volition, because it is placed opposite to the face, which contains the chief organs of sense. The expression opposite as to function has no specific meaning. It cannot indicate a counteraction; if this were the case, the ears, which are situated opposite to one another, should act in opposition to each other.

I must repeat Mr. A. Walker's supposition in his own words :"From the peculiar opposition which subsists between the situation of the face and cerebellum, we are entitled to expect a similar opposition in their functions. As the face, therefore, occupied by

Anat, et Phys. &c. pl. ii. fig. 6.

the chief organs of sense, is the seat of sensation, so we might expect the cerebellum to be the organ of volition. This supposition receives additional force from the consideration that, as the organs of sense and the cerebellum are the first and the last portions of the nervous system; so sensation and volition are the first and the last of its functions. But this supposition is completely confirined when we recollect that the degrees of voluntary power always bear a close analogy to the various magnitudes of the cerebellum."

If we desire to listen to, or to look at, any object, the muscles support the action of seeing and of hearing: hence sensation and voluntary motion are not in opposition. It is also quite erroneous to suppose that only the posterior nerves of the spinal mass go to the muscles, and the anterior to the organs of sensation; and it is incorrect to believe that almost all the parts of the body have filaments of ascending and filaments of descending impressions. The two roots of nerves of each half of the spinal marrow, namely, the anterior and posterior, go to different parts of the body; and it is erroneous to admit that filaments of the anterior and posterior fasciculi of the spinal mass of nerves go to almost every part the muscles and skin of the back receive their nerves from the posterior roots, whilst the muscles and skin of the abdomen receive theirs from the anterior roots, and yet the fore and back parts of the body have sensation and voluntary motion.

Mr. Alexander Walker, in considering the cerebellum in opposition to the face has neglected to take any notice of the brain. Does he therefore consider that part to have nothing to do with sensation and volition?

The degree of voluntary power bears no proportion with the size of the cerebellum.

Gall and Spurzheim have shown that the cerebellum in children is much smaller in proportion than in the adult, and yet children have more of muscular agility than adults.

The large shark described in the Philosophical Transactions for 1809 and 1813, an animal said to have the greatest locomotive power, has a remarkably minute cerebellum. See vol. an. 1809, pl. xix. a, and pl. xx. a a.

Swallows, which possess amazing locomotive powers, have a small cerebellum; and Cuvier has shown (Leçons d'Anatomie Comp. tom. ii. p. 153), that the proportions of the cerebellum and cerebrum in the bull and in man are absolutely the same, yet their ' degree of voluntary power is very different. It is true that fishes" have a larger cerebellum in proportion to their brain, and that they' possess a very strong locomotive power; and the rongeurs have likewise a very large cerebellum; and many of them, as the hare, squirrel, &c. possess a great locomotive power; but this is no general principle.

I shall here subjoin a few comparisons of the cerebellum aud

brain extracted from Cuvier (loc. cit.), and show that there is really no proportion between the degree of voluntary motion and the size of this organ.

1-9

1-8

1-7

1-6

1-5

1—41

1-34

1-3

1-2

Mr. A. Walker has further observed, that " Dr. Spurzheim has most certainly erred in denominating the cerebellum the organ of amativeness.' I have not time to give the facts which have led Drs. Gall and Spurzheim to hold this opinion, and must therefore refer to Dr. Spurzheim's work on the Anatomy and Physiology of the Brain, where the statements are fully detailed.

I am, dear Sir,

Your obedient servant,

WM. ELFORD LEACH.

ARTICLE VII.

On Pyrophorus, and the making of Potassium. By Dr. Hamel.

In the appendix to vol. iv. of Priestley's Experiments and Observations relative to various Branches of Natural Philosophy, p. 481, mention is made of the following experiment of Mr. Wm. Bewly:"I mixed equal parts of sal-tartar and vegetable or animal coal, or sometimes three parts of the former with two of the latter, and calcined them in the usual manner (for making Homberg's pyrophorus). This composition, on being exposed to the air, generally kindled in the space of half a minute or a minute. It did not burn with so much vivacity as the vitriolic pyrophori, as it contained no sulphur. I shall hereafter denominate this the alkaline pyrophorus. It differs in no one circumstance from M. du Suvigny's neutral pyrophori, except in its not containing that very principle to which he ascribes their accension. Lest it might be suspected that the salt of tartar which I employed might accidentally contain vitriolic tartar, or vitriolic acid, I repeated the experiments with tartar calcined by myself, as well as with nitre fixed or alkalized by deflagration with charcoal and with iron filings; but in all these

cases the event was the same. It is rather surprising that this alkaline pyrophorus should not have been discovered before, as I have more than once, since I first noticed it, on preparing the Prussian alkali, seen the lower part of it take fire soon after its having been turned out of the crucible and bruised, even when the matter had not been covered with sand."

If these experiments of Mr. Bewly be correct, they evidently show that the inflammability of Homberg's pyrophorus depends (at least partly) on the mixture of potassium (and perhaps also alumina) with fine powder of charcoal, and that the common theory, according to which the inflammability of pyrophorus depends on the sulphuret of potash, imbibing moisture from the atmosphere, and by that means setting at liberty heat enough to inflame the charcoal mixed with it, is insufficient. It appears that Mr. Bewly followed nearly the same method in order to make his pyrophorus, as Bucholz, Tromsdorf, and Curaudau, did with a view to obtain potassium; and if Mr. Bewly had happened to introduce into the vessel containing the heated mixture a cold metallic body (as Curaudau did in order to collect the potassium which is formed during the process, and driven off in vapours), he would have seen more than 30 years ago one of those bodies by the discovery of which Sir Humphry Davy's name is now immortalized. As Mr. Bewly's experiment was inconsistent with the then prevailing theory, there was hardly any attention paid to it, though it was published as long ago as the year 1779; at least I do not recollect that it was repeated. I found that an alloy of potassium with iron is a pyrophorus also. When I prepared potassium the first time, in the way which Gay-Lussac and Thenard describe, I did not know the property of this alloy; and having cut off that part of the barrel containing the potassium, I began to scrape it out, holding the barrel over a glass bason containing petroleum. I had poured out my whole stock of petroleum, perhaps two pounds, into this bason, that I might be able to immerse into it the whole piece of the barrel, in order not to lose any potassium. After I had scraped out that portion occupying the centre of the barrel, which is the purest, I came to that in immediate contact with the inner surface of the barrel itself, which is generally alloyed with iron; and a small piece of this alloy, being just scraped off, and having therefore its surface quite free from oxide, in falling down took fire, by coming in contact with the air, and lighted the petroleum contained in the glass bason, which cracked, and, the burning fluid flowing over my clothes, placed me rather in a dangerous situation. I afterwards have seen the same effect frequently. I think this pyrophorus of potassium and iron leaves no doubt that there may be one consisting of potassium and charcoal merely; and this will throw light on the nature of Homberg's pyrophorus.

In order to obtain a potassium free from iron, I several times followed a method which is very simple, and on that account de

serves perhaps to be known, though it did not yield me quite so large a quantity as the apparatus of Gay-Lussac and Thenard, which, however, does not yield so good potassium, and comes much more expensive. I have made a good deal of potassium, and found, 1. That the chief secret to obtain it in considerable quantity is to use a very strong fire, in order to drive every particle of it over. 2. To prevent the barrel from melting in such a high degree of heat a good tube is wanted. 3. The barrel, notwithstanding these precautions, will generally serve only once. 4. For this reason all the contrivances, where there are different parts combined by grinding them together, or by means of screws, come too expensive, as they are lost after having been used once. I used to make my potassium in old gun-barrels, which were bent (like GayLussac's and Thenard's) in two places, and had no other piece added to them. The middle part of this barrel is placed almost horizontally (only a little elevated towards the open end) through a cylindrical furnace, and contains the iron turnings; the thicker end, which projects on one side from the furnace, is bent upwards, and contains the potash. It can easily be tightened by screwing in the breach, and putting a little clay into the touchhole. To the open end, which projects on the other side from the furnace, and is bent downwards, at first I adapted, as the French chemists did, a receiver made of iron, from which a tube descended into a vessel with quicksilver. I likewise, according to their prescription, screwed into the upper part, containing the potash, an iron tube, the end of which was placed under mercury also; but I found this to be a very troublesome and expensive apparatus, as I could not use it a second time; nor did I always observe the gas coming out through the quicksilver, as it would find its way out somewhere else, either where the receiver was adapted, or where the pipes were screwed in. Finding, therefore, these pipes quite useless, I closed the upper end of the barrel, after the introduction of the potash, entirely by screwing in the breech and putting some clay into the touchhole, and instead of adapting to the lower end any receiver, I put this end, open as it is, into a small iron bason, containing a little vegetable oil previously well heated, in order to drive off the watery particles. (Petroleum could not be used for this purpose, as it would be set on fire by the gas, and even by the heat of the furnace.) When the formation of potassium was going on, one bubble after the other of hydrogen gas holding potassium in solution rose through the oil, and coming in contact with the air took fire, like phosphoric hydrogen gas, but with a more considerable explosion. The purest part of the potassium run down in drops into the oil, in which it rose to the surface, from whence I took it with a spoon, and put it into petroleum. The potassium so obtained did not contain any iron, but was of a very bright lustre, much like silver, whereas that collected in the barrel is generally alloyed with iron, and of a bluish colour, more like lead. Living near an iron