show what caution is essential in the opera- | a series of phenomena, and emerged from tions of experimental philosophy. Let me that series with a purely intellectual constate wherein I suppose this oversight to conclusion, our duty is to bring that conclusion sist. I have here a metal cube with two of to its crucial test. In this way we fortify its sides brightly polished. I fill the cube our science, sparing no pains, shirking no with boiling water and determine the quan- toil to secure sound materials for the edifice tity of heat emitted by the two bright sur- which it is our privilege to build. If, then, faces. One of them far transcends the oth- our alleged facts be real, and if our inferer as a radiator of heat. Both surfaces ap- ence from these be just, we ought to find. pear to be metallic. What then is the that inference ratified by experiment. For cause of the observed difference in their the purpose of testing it I take two powradiative power? Simply this: I have ders of the same physical appearance: one coated one of the surfaces with transparent of them is a compound of mercury and the gum, through which, of course, is seen the other a compound of lead. On two surmetallic lustre behind. Now this varnish, faces of this cube are spread these bright though so perfectly transparent to luminous red powders without varnish of any kind. rays, is as opaque as pitch or lampblack to Filling the cube with boiling water, and denon-luminous ones. It is a powerful emitter termining the radiation from the two surof dark rays; it is also a powerful absorber. faces, one of them is found to emit thirtyWhile, therefore, at the present moment it nine rays, while the other emits seventyis copiously pouring forth radiant heat itself, four. This, surely, is a great difference. it does not allow a single ray from the metal Here, however, is a second cube, havbehind to pass through it. The varnish ing two of its surfaces coated with the then, and not the metal, is the real radiator. same powders, the only difference being Now Melloni, and Masson, and Courtépée that now the powders are laid on by experimented thus: they mixed their powders and precipitates with gum-water, and laid them by means of a brush_upon the surfaces of a cube like this. True they saw their red powders red, their white ones white, and their black ones black, but they saw these colours through the coat of varnish which encircled every particle of their powders. When, therefore, it was concluded that colour had no influence on radiation, no chance had been given to it of asserting its influence; when it was found that all chemical precipitates radiated alike, it was the radiation from a varnish common to them all which showed the observed constancy. Hundreds, perhaps thousands, of experiments on radiant heat have been performed in this way by various inquirers, but I fear the work will have to be done over again. I am not, indeed, acquainted with an instance in which an oversight of so trivial a character has been committed in succession by so many able men, and vitiated so large an amount of otherwise excellent work.

Basing our reasonings then on demonstrated facts, we arrive at the extremely probable conclusion that the envelope of the particles and not the particles themselves, was the real radiator in the experiments just referred to. To reason thus, and deduce their more or less probable consequences from experimental facts, is an incessant exercise of the student of physical science. But having thus followed for a time the light of reason alone through

means of a transparent gum. Both surfaces are now absolutely alike in radiative power. Both of them emit somewhat more than was emitted by either of the unvarnished powders, simply because the gum employed is a better radiator than either of them. Excluding all varnish, and comparing white with white, I find vast differences; comparing black with black I find them also different; and when black and white are compared, in some cases the black radiates far more than the white, while in other cases the white radiates far more than the black. Determining the absorptive power of those powders, it is found to go handin-hand with their radiative power. The good radiator is a good absorber, and the bad radiator is a bad absorber. From all this it is evident that as regards the radiation and absorption of non-luminous heat, colour teaches us nothing; and that evenas regards the radiation of the sun, consisting as it does mainly of non-luminous rays, conclusions as to the influence of colour may be altogether delusive. This is the strict scientific upshot of our researches. But it is not the less true that in the case of wearing apparel- and this for reasons which I have given in analysing the experiment of Franklin-black dresses are more potent than white ones as absorbers of solar heat.

Thus, in brief outline, I have brought before you a few of the results of recent inquiry. If you ask me what is the use of them, I can hardly answer you, unless you

define the term use. If you meant to ask me whether those dark rays which clear away the Alpine snows will ever be applied to the roasting of turkeys or the driving of steam-engines, while affirming their power to do both, I would frankly confess that I do not think them capable at present of competing profitably with coal in these particulars. Still they may have great uses unknown to me; and when our coal-fields are exhausted, it is possible that a more ethereal race than ourselves may cook their victuals and perform their work in this transcendental way. But is it necessary that the student of science should have his labours tested by their possible practical applications? What is the practical value of Homer's Iliad? You smile, and possibly think that Homer's Iliad is good as a means of culture. There's the rub. The people who demand of science practical uses, forget, or do not know, that it also is great as a means of culture; that the knowledge of this wonderful universe is a thing profitable in itself, and requiring no practical application to justify its pursuit. But while the student of nature distinctly refuses to have his labours judged by their practical issues, unless the term practical be made to include mental as well as material good, he knows full well that the greatest practical triumphs have been episodes in the search after natural truth. The electric telegraph is the standing wonder of this age, and the men whose scientific knowledge and

*

mechanical skill have made the telegraph what it is are deserving of all honour. In fact, they have their reward, both in reputation and in those more substantial benefits which the direct service of the public always carries in its train. But who, I would ask, put the soul into this telegraphic body? Who snatched from heaven the fire that flashes along the line? This, I am bound to say, was done by two men, the one a dweller in Italy, the other a dweller in England, and therefore not a thousand miles distant from the spot where I now stand, † who never in their inquiries consciously set a practical object before them, - whose only stimulus was the fascination which draws the climber to a never-trodden peak, and would have make Cæsar quit his victories to seek the sources of the Nile. That the knowledge brought us by those prophets, priests, and kings of science is what the world calls useful knowledge, the triumphant application of their discoveries proves. But science has another function to fulfil, in the storing and the training of the human mind; and I would base my appeal to you on the poor specimen which has been brought before you this evening, whether any system of education at the present day can be deemed even approximately complete in which the knowledge of nature is neglected or ignored.

JOHN TYNDALL.

* Volta.
† Faraday.

A WALK FROM LONDON TO THE LAND'S this country, and to collect information that END AND BACK.- With Illustrations. By might be useful to American farmers; he has Elihu Burritt. (Sampson Low, Son, and certainly adhered to this design, and in the Marston.)-We can forgive this genial critic chapter on the Wiltshire labourers discusses the some slight inaccuracies in English history, subject of wages in a way that is well worthy and just the least tendency at times to fine of the attention of the employers of labour in writing after the American fashion. If he has those parts; but he by no means confines himadded a crime to King Harry's list, already self to these topics. He writes pleasantly about "long enough to hang a common sinner," in the old towns and their historical associates the taking off Jane Seymour's head, he has made cathedrals, the baronial mansions and parks,and compensation by bestowing on the lady "vir- even the legends, such as that of the Glastontues enough to make a saint," which we never bury thorn. As he is satisfied with the people heard of before; and his ambitious phrases, that he has visited, having "never experienced such as "tomb-fonts" and "home-stars," are any disagreeable treatment, nor been subjected few and far between. Generally he writes sen- to any inconvenience worth mentioning," sibly and with just the amount of friendliness though he has "measured the length of the that Englishmen most appreciate, the friendli- island and doubled it half way back on foot," ness that arises from a recognition of relation- so are we with our visitor. We recognize the ship in ancestry, in temperament, and in aim. The leading motive of this, as of his previous "Walk," was, it seems, to see and note the agricultural system, aspects, and industries of

judgment and the kindliness with which he has observed us, and we cordially recommend the perusal of his volume. - Spectator.

When both our hearts were full of glee, WHO says that Shakespeare did not know his In many a dance and courtly show I had you for my vis-à-vis.

66

shy, though his shyness was not awkward like his friend Lorimer Boyd's.

you must

"I was glad to amuse her. But not be angry with Kenneth for laughing a little: I had no idea it was a monkey that Lady Charlotte was so anxious about when I first saw her distress."

Gertrude shrank a little farther from her companion, and spoke in a low voice.

"I know; I was not exactly angry; but it vexed me. Mamma is not-that is, I mean, she is not one of those clever women with strong nerves, who do nothing that any one can smile at. I know mamma is not clever; but she is good and tender; she is tender to all she loves; and she is tender to all creatures - birds, and pets of all kinds. My poor father used to give them to her; he died of consumption, and he used to have them in his room; it is true he did not give her Zizine, but mamma has the habit of loving these things extremely — and - and I cannot bear that any one should seem almost to jest at her vexation."

She trembled a little as she spoke; but that trembling-like the tremolo in her clear rich singing-gave no impression of weakness; and the touch of sternness was in her voice again at the final phrase, as it had been when she said that Kenneth

go without it; and even ventured to hint that the valued Antonio himself must originally have been a stranger to Zizine, since she was brought from the Brazils; a remark which seemed to make a profound impression on Lady Charlotte, who pronounced it to be so true; so very true and-and so very comforting;" and she was quite surprised it had never occurred to, her before. "But you know, Sir Douglas Columbus's egg you know!" And on seeing rather a puzzled acquiescence in her new friend's face, she further explained herself by adding, "what nobody thought of till they saw it done, you know!" and with a tearful smile she gave a final flourish of the embroidered pocket-handkerchief, and settled herself for more cheerful discourse. Then she listened with rapt attention to a number of little anecdotes told by Sir Douglas, of instinct and wisdom in animals, such as would be narrated to an intelligent child; and when he wound up with the tragic incident of the suicide from grief, of a male marmoset whose little mate dying on shipboard, was thrown overboard; and told how, the very first day his cage was left accidentally open, the melancholy little survivor leaped over the ship's side at that identical spot, into the waves; and described the regret of all the sailors, who were of opinion that the knew Zizine." Sir Douglas liked her for ship should have been put about, though in it. He liked the protection given by her wild weather, rather than that Jocko should own child to this sacred silly woman: sacred have been allowed to perish, Lady Char- as a parent, even where weakness could lotte vehemently exclaimed, "Oh! I think not but be perceptible; sacred for the sake so too-I think so too!- How very cruel of duty and for the sake of scenes reof the captain!" And as she and her plete with sadness and reverent associaguests stepped forth into the garden, and tions: not to be laughed at by mockpaced along the terrace, and through the ing lips; to be pitied, to be tenderly dealt Pergola shaded with vines, she remarked with, even as she dealt, or was supposed to Kenneth that she had never seen a to deal, with others. He felt that had more pleasant or gentlemanly man than his he been the son of a silly mother he also uncle "and so travelled, too"- which would have dealt so by her; and his own phrase she explained, like Columbus's egg, mother's half-remembered, halt-forgotten and said she meant that he knew so many face, vaguely rose again to memory in presthings, which, of course, he had picked up ence of this girl, as it had done the evening going so much about the world as she un- before leaving the impression, as it did derstood he had done. then, that Gertrude Skifton "had a look of And Gertrude too praised Sir Douglas, her about the eyes." Dear eyes, that bent even to himself! She was leaning against over his cradle, and were lifted to Heaven one of the square stone supports of the when he first learned to pray, and shone for loggia, the vine leaves with their tendrils a little way on in his childhood, and then dropping and curling round her uncovered vanished, leaving in those childish years head, pausing to let her companion admire such a comfortless blank of love. the distant view of land and sea.

"It was

When he left the Villa Mandóno with very kind of you," she said, "to amuse Kenneth, they walked a little way in mamma; it took away all her nervousness." silence; then Kenneth said, laughing, Sir Douglas flushed a little. It was very "Well, we had a fine scene there! That pleasant being spoken to in such a friendly woman is an incarnation of folly, but the tone by this pretty girl; and he was rather girl is very nice."