POUILLET.

"Monsieur Pouillet has (with the single exception of Dumas) the largest class which the Sorbonne exhibits; the number of his pupils cannot be less than 600; indeed, it is probably considerably above this calculation. He seems to be about fifty, has keen hazel eyes, and a pleasing physiognomy, and lectures with that perfect ease, which none but a man thoroughly possessed of, and by, his subject, can assume. As the following passages were then new to me, some of them may probably be so to others.

A contracted muscle, or one in the act to contract, increases prodigiously in force, by the closer approximation of its molecules; this is partly because as it diminishes in length it necessarily increases in thickness; but the difference of cohesive strength or tension between the living and the dead muscles depends mostly on the vessels which pervade the former being full during life, whereas after death they are of course empty; while they are full, the force applied to the muscle acts equally upon all its fibres, and the tension of all parts being equal, the force is equally divided; thus the strength of a wet cord or cable is far greater than that of a dry one of the same thickness, because the penetrating moisture gives an equality of tension to its fibres.'

666

The power of adhesion noticed between two bodies placed in juxtaposition, with a layer of fluid between, is not attributable, as commonly stated, to the partiality of atmospheric pressure; this is proved by putting two moistened surfaces of glass in contact, fastening a weight to one, and then placing them in vacuo, the weight will be found to remain suspended; that is, the thin layer of fluid interposed has a double adhesion, by its two surfaces, to the two solid surfaces with which it is in contact, and which it thus chains together. The action of all glues and pastes is of this nature, and is twofold. First, they act merely like water interposed between the two flat plates of glass, filling up the interstices of the bodies to be united, and so multiply the points of adhesive contact, and when they dry, the bond of adhesion becomes solid and confirmed. So, for I like to apply knowledge to knowledge, in what Hunter calls union by the first intention' (and what Aretæus had spoken of in almost identical phrase-xxla gwlov σxoπov*), lymph (which is a fluid cement) is first effused; afterwards, as the liquid parts are becoming absorbed, the lips of the divided surfaces are more nearly approximated by the constantly attenuating layer, till they are brought within the sphere of mutual and permanent attraction.""

This account of M. Pouillet is not so full as we could wish it. He is, however, a man so simple in his manners, and beset with so few eccentricities of character, that it is very difficult to give any marked outline of his manner, notwithstanding that he is the most popular, if not the best, lecturer in Paris. His characteristics, however, are fluency of language, clearness and occasional eloquence of description, zeal in his cause, ease of manner, and constantly animated mode of expressing himself. He is certainly the finest talker we ever heard, and the most perfect master of the crayon we ever saw. His outlines on the "old slate" rival in precision those of mathematical instruments. His principal attraction, however, is that perfect absence of self-esteem and pompousness of manner, so peculiar to lecturers of this country. M. Pouillet is the antipodes of a "Doctrinaire ;" and the object of his experiments and lectures appears to be less to instruct

* At first sight.

his class than to advance or investigate those branches of science to which they refer. The lecturer and his pupils gradually forget their different relations, and work together as labourers in one calling,fellow-gleaners in the same field of science. The degree of sympathy which exists between them is surprising; and the smile of M. Pouillet, his earnestness, his delight in the success of his experiments, his admiration of the grand laws of nature-all find an echo at once in the breasts of his auditory, for he and his class are identical and the same.

This state of things is to be found to the same extent in no other class-room in Paris; and though it is said that there are other lecturers more profound, we think there are none from whom so much is gleaned, and that too so agreeably, as from M. Pouillet.

We shall have nothing to add to the limning of the professor of Vegetable Physiology,

MIRBEL.

"Mirbel is a very clear, unaffected lecturer, a most worthy colleague of Blainville and Jussieu; he looks like one of his own dried plants, perfect in its anatomy, but sapless withal. He adopts a quiet conversational manner, and considers extreme accuracy in what he states to be so imperative, that if he occasionally forgets himself, he always apprizes his class of the

error.

"More fond of accurately ascertaining natural phenomena, than of imagining theories to explain their laws, or make them more striking or attractive, he truly observes, that almost any fact in nature is more beautiful, than the most excursive fancy can render it. His unreserved manner of stating his own changes of opinion, makes it evident that he is of the few who do not fall into the error of concluding from partial views or first ideas, and then assuming, as our doctors do, a purely hypothetical generalization as an axiom of science.'

66

"The procedure by which the bark of trees splits and peels off from the stem, was thus explained-the green envelope or bark (which, by the way, owes its colour to a minute portion of green pigment contained in some very minute utricles of the vegetable texture) begins to split so soon as it has ceased to form these utricles in sufficient quantity to meet the exigency of the increasing diameter of the tree. Thus, in some trees, a very few years are found sufficient to effect many and large lacerations of the bark. 'Respecting the well-known fact in rural economy, of the necessity of changing crops of not requiring the same land to do the same thing twice in succession, the following excellent remarks were made. Every farmer knows that he is obliged to vary his crops, nor does he ever think of exacting corn for two successive years from the same piece of land; but few are probably aware of the many explanations which have been proposed, to explain this apparent caprice in the earth. When it had been ascertained that any pivoting plant (as turnips for example) flourished upon the soil. where the year before the læta segetes* had waved their yellow corn, this was supposed, by some writers on agriculture, to result from the radicles of this class of plants having a power to make their way through the already impoverished superficial layers, and striking deeper into a virgin soil where the power of sustentation was yet unimpaired. To this hypothesis it may be objected, that were the elements of nutrition and growth contained in the earth, and these all that plants required for their support, then it would be

* Gay crops,

sufficient to manure the corn-field of the year preceding, to make it capable of a second year's crop. This, however, is contradicted by experience. Pictet's account is not more satisfactory. This writer supposed that the circumstance of turnips succeeding corn (or of the succession of crops to each other generally) was probably owing to different plants requiring and withdrawing, not the same but different elements, the supply of any of which being limited, the earth is amerced of some new and sustaining principle by every succeeding crop. This explanation, however, assumes that plants have a power of selecting their nutritive materials, an assumption not only hypothetical, but wholly contradicted by experience; for plants are observed to take up indifferently all substances soluble in water. The speculation of Decandolle is a third unsuccessful attempt, viz. :—that the excretions from plants during their growth may act as poisons to the earth, and, after a certain time, so injure it, as to prevent the further growth of a plant that may have recently flourished there. Such excretions he supposes to be emanations from the root, the remains of those juices which the earth and air conjointly supply, and upon which, in reality, the plant exists. But against even the very fact mentioned by Decandolle in confirmation of his opinion, that opium strewed upon the ground kills plants and renders the soil henceforth unproductive, we may quote the much more apposite fact, that trees (and why not therefore, à fortiori, corns and grasses) grow and flourish for entire centuries in the midst of excretions from their roots.' Mirbel's own explanation is simple, and we think satisfactory. Plants require other elements for their support, besides the elements of assimilation, and cannot thrive without them-for instance, there is silex in the cane, and there is lime in certain plants whose organization could not be complete without it. The quantity of any such foreign ingredients in a plant is generally very small; but the necessity for it may be presumed absolute. Plants cannot be constituted unless all the materials they require be furnished to them; and indeed the same observation will apply to animals; deprive a hen of lime, her eggs will have no shell; deprive animals generally of salt, and you ruin their power of digestion; deprive the earth then of its soda, and you must supply its place by potash; for salts are the excitants of the growth of plants, and of the clovers in a very remarkable manner. The smallest quantity of sea-salt has frequently been found to effect wonders in vegetation. But the spontaneous formation of any of these salts is the result of very slow chemical changes, which have been at work for centuries, and when the natural and very limited supply is exhausted (as it soon will be, if the earth be forced to give her increase), the corn of every succeeding year deteriorates, the field looks shabby, becomes chlorotic, and pines away; but allow the corn to fall where it grew, the earth will re-assume the salts extracted from it during such growth, and the same grain will continue to flourish indefinitely -in short, a peck of salt is worth a ton of manure, and it is to the understanding of this fact that we may attribute the luxuriance of the environs of Paris, where the soil is naturally of the poorest kind, but is made, by this simple addition, to yield its unequalled produce, and to fill its flower and its fruit markets with plenteousness.'

M. Thenard, Le Baron! is one of the professors of chemistry, and M. Dumas is another. They are thus placed in juxtaposition.

"Two savans, the most unlike in their manner, their mode of lecturing, their voice, their ensemble, but passing for equally good chemists, give alternate courses, and instruct unusually large classes."

We shall separate the pair, for the purpose of extending the first, at least, to somewhat of a whole length. He is too remarkable as an individual to be blended or associated with any other; and therefore, though it may be with a feeble pencil, we shall attempt to fill in some of the blanks left on the canvass by our great master. The following is all he has put in of

THENARD.

"Monsieur Thenard is an elderly person, and of somewhat unpleasant accueil. I understand, however, that he (like many others) finds it convenient to have two manners, and I here speak only of his every day one of conducting himself to strangers. He appears to pride himself more upon his peerage than upon his chemistry; is notoriously choleric, and detonates upon the object nearest to him like one of his own chlorides. As wordy as Isæus, and having a good wind, he can scold indefinitely. He speaks loud and without hesitation, but often drops his voice at the most important word of his sentence, leaving you an enigma to make out, instead of a truth to put by. His recommendation to carry a piece of quick-lime with you in case of cold, and no fire accessible, was at that time a novelty. You can get cold water,' he observed, ‘everywhere, and your lime has only to be slaked in any covered vessel, to afford a really excellent foot-warmer-indeed you may cook your cutlet on a metal plate, under which lime is slaked.""

Thinking this is incomplete, we have ventured to put in the following detail. The same remark may be made as to his appearance as has been applied to his accueil, for no one can look on his broad face, black, curly, long hair, capacious forehead, quick, penetrating, and cunning eye, long upper-lip and wide mouth, together with his squat and generally dirty person, and pronounce it to be otherwise than unpleasant. Every observer, however, would at once set him down as a most active-minded, but odd-looking, personage, possessed of a great deal of very strong sense, but in whose character irritability, and a love of fun, are the marked peculiarities.

He is a very different lecturer to M. Pouillet; he is more familiar with his pupils, and there is more plaisanterie passing between them; his style is extremely amusing and facetious, and frequently his lecture cannot proceed for minutes, owing to the convulsed laughter of his pupils. He has gained the name, amongst the students, of "Le Farceur de la Sorbonnet ;" and his theatre is filled almost as much by those who go to enjoy his jokes, as those who go to profit by his lectures. His face is watched most intently; and when his eye brightens, and his head is archly turned on one side, the joke is known to be on its way, and the pupils hail its coming with grins of merriment, or with peals of laughter. M. Thenard's last piece of buffoonery is as much the subject of conversation at the Sorbonne, as was "Lord Norbury's last" in the Irish courts of justice.

On

M. Thenard is, therefore, an amusing companion for an hour and a half, but we doubt whether chemistry is benefitted by his witticisms. many occasions, he descends from the philosopher to the buffoon, and draws his class down with him; whereas M. Pouillet, by being the earnest * Manner of receiving a person.

+ The master of Demosthenes; he composed sixty-four orations.

The Jester of the Sorbonne.

minister of science, raises his hearers to the level of the philosopher. The one creates a thirst for knowledge in the student, the other jokes for his leisure hours.

His style is full of light and shade, and is more stormy and abrupt than that of any one we ever heard. He is excessively fond of placing himself in a dilemma-of inquiring of his class how he is to extricate 'himself,―suggesting means that he knows will not answer, and then, after playing with and enjoying the embarrassment of his audience, he jumps unexpectedly upon the remedy, and laughs at the surprise and ignorance of his pupils. In his tones, in his reasonings, and in his experiments, his sole object seems to be-effect; he delights more in astonishing than convincing; and, as might be expected from such a character, he is vastly rapid in his movements, and impatient in his experiments. It is then that the irritability of his disposition most shows itself. We recollect once witnessing an experiment, during which he had thrown himself into a dilemma, like the one we have already mentioned; and after suggesting one ineffectual remedy after another, he at last, with a view to take his audience by surprise, and to liberate himself at once, exclaims, “ Mais, nous n'avons pas encore essayé avec de l'acide sulphurique." ["But we have not tried sulphuric acid yet."] The words were hardly uttered, before he bounces from one end of his table to the other, and with a self-satisfied grin upon his countenance, seizes upon the bottle, when lo and behold-it is empty! His fury at the disappointment cannot be conceived, much less described. Turning upon M. Barouel, his assistant, with the spring of a tiger, and raising up both his hands above his head, he screams at the top of his voice," Mon Dieu, Mon Dieu, Monsieur Barouel, où est l'acide sulphurique? Où est votre tête, Monsieur Barouel. Croyez vous qu'on peut faire des expériences sans tête et sans acide sulphurique?" ["Good Heavens, Good Heavens, M. Barouel where is the sulphuric acid? Where are your brains, M. Barouel? Do you think that any one can make experiments without brains and without sulphuric acid?"] M. Barouel explains to him that the bottle was full at the commencement of the lecture, and that he had himself emptied it in his experiments. The class roars with laughter, and M. Thenard more than any one else. When silence is re-established he draws M. Barouel forwards, clapping him gently on the back, and looking archly at his class, he says, "C'est un bon enfant celui-ci, Messieurs (M. Barouel is at least fifty years old,) c'est un excellent enfant. Mais il perd la tête quelquefois, et quelquefois aussi de l'acide sulphurique; et cette fois-ci j'ai cru qu'il avait perdu tous les deux." ["He is a capital boy, gentlemen, an excellent lad; but he sometimes loses his brains, and sometimes the sulphuric acid; this time I really thought he had lost both!"] Another laugh from his class; more acid is brought, and he continues his experiment.

In his laboratory, or after his lecture, he is very affable with his pupils, and always encourages them to ask him for explanations of any parts of his lectures which they may not have understood.

The pendant* to M. Thenard is thus delineated.