tion of the tree. 9. With exclusion of trans. piration, and therewith of rise of sap, the temperature of the tree is simply dependent on that of the air. 10. A simultaneous cooling of the lower and upper part of the tree completely equalises the amounts of influence (opposite according to the height of the stem) of the two cooling "moments." MOTION AND HEAT.-M. Ollivier (in the Journal des Débats) gives the following experiment in illustration of the conversion of motion into heat :-One end of a square bar of steel, in this instance 15 mm. X 70 or 80 cen., is held by one hand in the middle, and pressed strongly against a rapidly-revolving emerywheel, by which means the extremity so applied becomes considerably heated. The hand at the middle of the bar does not feel any change of temperature, but that at the other extremity is soon obliged to let go, the temperature rising to the point of burning the skin. M. Ollivier thus explains this effect, which appears paradoxical at the first glance. The heat that burns the hand is not generated at the other extremity of the bar and transmitted from thence, but is produced directly at the place. Movement and heat being synonymous, the movement destroyed by the hand at the outward extremity of the bar by the stoppage of the vibrations is converted into heat, whilst there being an interval of repose at the middle of the bar, no heat is perceived. A curious feature of the experiment is, that at the outer extremity the thermometer does not show any exceptional temperature, because the thermometer does not stop the vibration. To produce the burning effect, the hand should grasp the end of the bar with force enough to arrest the movement. DISCOVERY OF NON-METALLIC RAYS IN THE SOLAR SPECTRUM.-A discovery of importance to science is announced by Dr. Henry Draper of Hastings-on-the-Hudson. It is well known to students of the spectroscope, that while the black lines that indicate the presence of metallic vapors are so abundant in the solar spectum as to leave no room for doubting that most, if not all, the metals are ignited in the sun, there is yet an absence of the lines that characterize nearly all the non-metallic substances. Hydrogen is excepted from this sweeping rule, but there are many reasons for classing that gas with the metals. Various theories have been put forward to explain the absence of non-metallic lines from the solar spectrum, and the fact has even been used to throw a doubt over the nebular hypothesis, which necessarily assumes that the constituents of the sun cannot greatly differ from those of the earth. Dr. Draper's discovery, if it be com confirmed, shows that at least one-and probably several-non-metallic substances are present in the sun. In a paper read before the American Philosophical Society jast month, he gave the details of experiments which appear to prove that oxygen forms one of the sun's constituents. Its presence is indicated in the spectrum, not by black, but by bright lines. To make this more apparent, Dr. Draper has photographed with the spectrum of the sun a 66 comparison spectrum" of common air-the air being ignited by the electric sparks of a Leyden jar. The " parison spectrum" gives the bright lines of oxygen and nitrogen, and also (from the terminals of the battery used) those of aluminium and iron. The lines of the metals serve to check the accuracy with which the two spectra of the sun and of air--are matched. These spectra are reproduced without the inAlbert-type process, and appear as a frontistervention of the engraver, by Bierstadt's piece in The American Journal of Science and lines on the solar spectrum showing the presArts. If it is conceded that there are bright discovery of the other non-metallic substances, ence of oxygen, it seems probable that the such as nitrogen, chlorine, sulphur, carbon, the sun's constitution will then follow, since etc., may be similarly made. A new view of the circumstance that bright lines flow from the non-metals indicates that their quantity in the sun is probably enormous as compared with the metals.—The Tribune. VARIETIES. ON CHOOSING A HOUSE.-Before you enter a house that you have some thoughts of taking, do not fail to take a look, not only at the exterior thereof, but at the neighborhood around it. Do not, however, be too much struck with a showy outside; the place may be but a whited sepulchre after all-a very living grave. The house, too, may be in itself, both outside and in, everything which heart can desire, but after all it may be situated in the vicinity of other houses, either at the back or front, the conduct of the inmates of which may render your life wretched. Your rooms may be furnished with taste and comfort, but if you are awakened every other night by the sounds of drunken revelry, or mayhap fighting and squabbling, your life will not be a very romantic one, to say the least. Again, however tastefully your garden may be gotten up, however shady and cool your summer-house, the sound of voices in altercation, or perhaps oaths and swearing, floating over the adjoining wall, will detract materially from the pleasure you derive from the society of a friend or favorite author. Having satisfied yourself regarding externals it will be time now to have a peep inside, and the very first thing it is your duty to find out is whether or not the house be damp or dry. Nothing can be more injurious to the health than residence in a house which is damp; coughs and colds, aches and pains and rheums -ay, and maybe fever itself-must be your portion if you are unwise enough to live in a damp house, and granting even that you have the strongest of constitutions, dampness will sap it, your nerves will be weakened, you shall find yourself ill and fretful without being able to assign a cause therefor. Avoid a damp house, therefore: you can hardly fail to know if it is damp. Suspicious spots of mildew about the paper, beading on unpapered walls, and a generally moist smell must guide you in your diagnosis. More deadly even than damp are the emanations from drains and cesspools and noxious gases, such as sulphuretted hydrogen and carbonic acid. If you mean to live for any length of time in a house, it will be much better to put the matter into the hands of a trustworthy surveyor, and let him see to this matter.-Cassell's Family Magazine. MR. S. C. HALL AND THE "ART JOURNAL." -In 1839 Mr. Hall conceived the idea of establishing a magazine devoted entirely to art, art manufactures, and the higher class of literary contributions, and launched the Art Union, which, under its somewhat modified and greatly improved title of Art Journal, he has continued uninterruptedly to conduct from that time to the present day, a period of thirty-eight years. 'When, in 1839, I commenced the Art Journal," says Mr. Hall, "there was no public for art literature; I had to create a public, and I did. The newspapers gave, on certain pressing occasions, a few lines to the theme. Now, column after column accords justice to the vital subject, criticising, fully and thoroughly well, all art productions, whether published or exhibited. There were in 1839 no buyers of pictures by British artists; there were plenty to purchase old masters-the works of Raffaelle and Titian and Canaletti; notorious frauds, which I continuously exposed, at much peril, and once at great cost, sometimes showing where false pictures were made, and printing, month after month, Custom House returns of 'ancient masters' imported into London; canvases that paid duty, but which the artists who were responsible for them had never seen. By persisting in that course, proving how little they were worth and would ultimately bring if re-sold, and at the same time producing proofs of the gradual rise in value of British pictures when submitted to public sale, I led the dealers on the one hand, and the collectors on the other, to avoid 'old masters,' and to patronise such as could be readily authenticated-the productions of artists who were yet alive to testify to their work. At the time to which I go back, artists sold their productions at very small prices indeed; they now sell at the auction rooms for, sometimes, a hundred fold the amount such artists received for them. I have more than once been present at a private view of the Royal Academy when, during the day, there was not a single picture sold. About 1840 I gave commissions for six fancy portraits to six young artists, then beginning a career in which they have since attained the highest eminence. Among the six were Frith, Ward, and Elmore. Each of the six painted six pictures for the sum of ten guineas each, and were content; they would now be estimated each at the value of two hundred guineas. But still more astounding is this fact: when the engraver Finden, for whom I had obtained them, and who had paid for them (they were for a work I edited for him, 'The Beauties of Moore'), sought to re-sell them at the sums they had cost, and with that view exhibited them at a gallery in the Strand, he could find no buyers at the price of ten guineas each. I need not tell you how different is the case now, when artists are among the wealthier classes of the community. You would gladly now give a hundred pounds for a picture which in 1839 you might have had for as many shillings; and you know that no investment is at once so secure and so remunerative as the money invested in wisely-selected pictures." The change thus evidenced Mr. Hall may justly claim to have a large share in producing. In 1839, as just stated, Mr. S. C. Hall founded, entirely himself, and on his own responsibility, the Art Journal, which has continued uninterruptedly to be published from that hour to this, and the whole of that time under his careful editorship. Changes have taken place in its proprietorship, in its size, and in its general style of issue, but the main features and the character of the work remain the same.- Leisure Hour. |