the appearances observed by M. Prévost "may be easily accounted for;" whereupon Dr Young retorts, "had Dr Wells been as solicitous to attend to the labours of his cotemporaries as he has been very laudably anxious to refer to those of his predecessors, he might have said, not that the experiments of M. Prévost might be easily accounted for,' from the properties which he mentions, but that they actually had been explained in a similar manner by one of his own countrymen. There are, however, some modern philosophers, who, whether from their own fault or from that of their hearers and readers, or from both, appear to be perpetually in the predicament of the celebrated prophetess of antiquity, who always told truth, but was seldom understood, and never believed; and the author of the lectures in question has not unfrequently reminded us of the fruitless vaticinations of the ill-fated Cassandra."

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Dr Wells published a reply to Dr Young's strictures in the Fifth Volume of the "Annals of Philosophy" (1815); and we now proceed to make a few extracts from it. He says, My explanation of the immediate cause of dew is grounded on the simple fact, that bodies always become colder than the neighbouring air before they are dewed, and was consequently open to the discovery of every person since the invention of thermometers. It is true, that the next step in my theory could not have been taken without the assistance of the late discoveries of others, and this has been amply acknowledged in my essay. My health at the time of its being drawn up was in such a state, that I scarcely hoped that I should ever finish my work, and my notes were so written that no person besides myself could make use of them. I composed, therefore, in haste, and had neither leisure nor strength to search public libraries for all the works which I wished to consult."*

* We learn from the "Memoir of his Life," dictated by Dr Wells in his last illness to his friend Mr Patrick, and prefixed to a work entitled, “Two Essays," &c., published in 1818, after the death of the author, a few particulars which throw some light on the loose manner in which the Essay on Dew was written. For example, he says,-" In 1800, I was suddenly seized with a slight fit of apoplexy. From this, however, I did not recover so far as to be enabled to return to the exercise of my profession for several months; and I never afterwards regained the complete possession of my memory. I became, too, much more unfit for the pursuits of any difficult train of thought which was

Dr Wells contends that Prévost "was ignorant that bodies on the surface of the earth become much colder than the air in a clear night; this being one of the principal facts on which my theory of dew is built."

We must here remark, that although Prévost was ignorant of this important fact, it had been made sufficiently clear by Patrick Wilson and Six, with whose experiments Dr Wells was acquainted. He states, however, that when he wrote his Essay he had not read the explanation of Prévost's experiments in Dr Young's Works. He read the fifty-first lecture and the sixtieth, but not the intermediate one which contained the explanation in question. He consulted Dr Young's work in a public library, and was in haste; and as he found no reference under dew in the index, he searched no farther. He admits Dr Young's conjecture as to the true explanation of Prévost's window experiments to be original. "It was most happy too, since, if admitted to be just, it completely accounted for several important circumstances in M. Prévost's experiments. If, then, its learned and ingenious author had established

the production of another person." He then goes on to say, that he was not, so far as he could ascertain, less equal to the pursuits of his own train of thought.

Referring to his inquiry into the nature of dew, which he thought would not occupy him more than a few nights, at the house of one of his friends in the country, he says, " I commenced it in the autumn of 1812, but soon found that I had greatly miscalculated the time which it would employ me. I determined, however, to proceed, from the natural steadiness of my disposition, which would never allow me to abandon any pursuit that I had seriously undertaken. I soon found that I was altogether unequal to it; for each night's labour fatigued me so much, that I could not undertake a second for several days after. In the meantime, my ankles began to swell in the evening, which I regarded as a mark of general weakness. At length I became so infirm, about the end of 1813, that I was absolutely obliged to give up any further visits to the country.

"In the beginning of 1814 a considerable snow having fallen, I could not resist the temptation of going for several evenings to Lincoln's Inn Fields, during a very severe frost, in order to repeat and extend some of Mr Wilson's experiments on snow. I soon, however, was obliged to desist." His symptoms became so alarming, that his friend, Dr Lister, thought he could not survive more than a few months. He says, “I set about immediately composing my Essay on Dew, as my papers containing the facts on which my theory was founded would, after my death, be altogether unintelligible to any person who should look into them. I laboured in consequence for several months with the greatest eagerness and assiduity, fancying that every page I wrote was something gained from oblivion."

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its truth by facts clearly seen by himself, and had afterwards pursued the subject of dew through its various ramifications by means of the clue which would have been thus obtained, he must soon have acquired a knowledge of the theory which has lately been submitted by myself to the consideration of the learned, and which he, as a member of that body, has pronounced to be just. But I must, on the other hand, be permitted to say, that, if Dr Young, forgetting that Newton became a glass-grinder in the service of science, will neglect to employ, for the increase of natural knowledge, the slow and laborious method of observation and experiment, and will frequently exhibit his speculations in a manner unsuited to the capacities of ordinary men, he ought not to think it strange that opinions advanced by him on difficult points of philosophy are not, agreeably to his own remark at the end of the criticism, received as truths beyond doubt, and are often not understood."

This is smartly said, but cannot, we think, be admitted as a sufficient answer to Dr Young's strictures.

It will naturally be asked, What then remains for Wells? If all the phenomena had been observed, and even the theory pointed out, before he began his experiments, is there any merit at all to which he can justly lay claim? We answer, that to Wells belongs the rare merit of seeing clearly where other men saw obscurely; of grasping the whole, while other men only held detached parts; of bringing the scattered and somewhat incoherent labours of other inquirers to bear upon his own experiments, which were undertaken with clearer views, and consequently a more direct purpose, than those of his predecessors; and the final result of his long and patient inquiry was the establishment of a theory of extreme beauty and simplicity, the truth of which subsequent inquiry has only tended to confirm: not that Dr Wells is to be ranked as the author of this theory, but that his Essay was, as Dr Whewell remarks,*"one of the books which drew most attention to the true doctrine, in this country at least."

Still, however, it is but an act of justice to rescue from oblivion the claims of such men as Le Roy, Pictet, Patrick * History of the Inductive Sciences. 3d edit. vol. ii. 1857.

Wilson, Prévost, and others. Honour to them does not diminish the merit due to Wells. It only restores to its proper course the progress of discovery, where in this, as in other branches of science, and indeed in other relations in life, men are as mutually dependent on each other for intellectual progress as they are for the supply of their ever-recurring daily wants. It is not given to one man to begin, continue, and complete the journey into the undiscovered land unaided and alone; others have preceded him in the attempt, and have left the impressions of their footsteps on the virgin soil, which, however faint and uncertain, serve nevertheless as guides to subsequent explorers.

The Theory of Terminal Fructification in the Simple Plant, of Ovules and Pollen, and of Spores. By Dr MACVICAR, Moffat.*

It is generally admitted, and indeed is obvious to every observer, that symmetry prevails to a great extent in the forms at once of the mineral, the vegetable, and the animal kingdom. Nay, it manifests itself most beautifully in the forms and orbits of the heavenly bodies, and in the phenomena of light and colours; and in a word, symmetry, makes its apparition, more or less, everywhere. But to this, it must be confessed, that there sometimes seem at least to be remarkable exceptions, and that, too, where one would naturally expect symmetry most to prevail. Of these one of the most striking is this, that in a simple plant, a plant with a single axis, the fructification is always terminal, so that, morphologically viewed, the fully developed plant presents its axis to us as terminated by the ugly root at one extremity, or pole, and by the beautiful inflorescence at the other-an arrangement in which all symmetry seems set at defiance. Now, why is this? Why are the flower and fruit always produced at the upper extremity of the stem, a position which (besides its disregard of symmetry) can be reached only after the

* Read before the Botanical Society, 13th December 1860.

plant has survived all accidents all near the close of life, and when one would suppose that is vital energy must be nearly exhausted, and the plant consequently little fitted for accomplishing this, which is nevertheless the most critical and the most important function of animated nature!

The only explanation which I have seen of this phenomenon, and others of a similar nature, consists in references to the condition of vegetable life at different periods of growth, these being again referred to the season of the year, or some external influence. But it is precisely the condition of vegetable life at different periods of growth which is wanted to be explained. Life, at every epoch in the development of the plant, is no doubt always co-ordinate with the work which it has to do at the time, alway adequate to accomplish the development proper to that epoch, if the environments of the plant fulfil their part. But this fact does not explain why the development of the plant is what it is, and not otherwise. The insufficiency of such a view, as also its plausibility, is, I think, well shown by the point in hand.

The terminal position of the fructification, it is said, is owing to the exhaustion of the vital energy of the plant, and the flower is, notwithstanding its beauty, the expression of exhausted energy. And in favour of this view it is, moreover, argued, with seeming cogency, that when the branch of a fruit-tree is injured, or a plant made to grow in a poor soil, it gives flower buds, whereas if it had been left free from injury, or had been grown in a rich soil, it would have given leaf buds only. And the entire explanation is closed by an appeal to what is indeed a beautiful provision in the economy of nature, viz., that when the life of the individual is in danger, an effort is made to develop the reproductive apparatus, so as to secure the life of the species, should the individual perish. Now, such an explanation seems to have everything in its favour. At first sight it seems wholly satisfactory. But it is only at first sight. Many things soon present themselves which are against it. Thus in the higher regions of the animal kingdom, those which are analogous to the region of flowering plants in the vegetable kingdom, it is found that the reproductive apparatus attaches to the period of highest physical