[From The Spectator.] A long-vexed question—one which astronomers and physicists have labored and puzzled and even quarreled over for two centuries at least—has at length been set at rest. Whether the moon really sends us any appreciable amount of warmth has long been a moot point. The most delicate experiments had been made to determine the matter. De Saussure thought he had succeeded in obtaining heat from the moon, but it was shown that he had been gathering heat from his own instruments. Melloni tried the experiment, and fell into a similar error. Piazzi Smith, in his famoiis Tenerifife expedition, tried the effect of seeking for lunar heat above those lower and more moisture-laden atmospheric strata which are known to cut off the obscure heat rays so effectually. Tet he also failed. Professor Tyndall, in his now classical " Lectures on Heat," says that all such experiments must inevitably fail, since the heat rays from the moon must be of such a character that the glass converging-lens used by the experimenters would cut ofi' the whole of the lunar heat. He himself tried the experiment with metallic mirrors, but the thick London air prevented his succeeding. The hint was not lost, however. It was decided that mirrors, and not lenses, were the proper weapons for carrying on the attack. Now, there is one miiror in existence which excels all others in existence in light-gathering, and therefore necessarily in heat-galhering power. The gigantic mirror of the Rosse telescope has long been engaged in gathering the faint rays from those distant stellar cloudlets which are strewn over the celestial vault. The strange clusters with long out-reaching arms, the spiral nebulse with mystic convolutions around the blazing nuclei, the wild and fantastic figures of the irregular nebulse, all these forms of matter had been forced to reveal their secret under the searching eye of the great Parsonstown reflector. But vast as are the powers of this giant telescope, and interesting as the revelations it had already made, there was one defect which paralyzed half its powers. It was an inert mass well poised—indeed, so that the merest infant could sway it, but possessing no power of self-motion. The telescopes in our great observatories follow persistently the motions of the stars upon the celestial vault, but their giant brother possessed no such power. And when we remember the enormous volume of the Rosse Telescope, its tube—fifty feet in length—down whici a tall man can walk upright, and its vast metallic speculum weighing peYeral tuna, the task of applying clock-motion tc so cumbrous and seemingly unwieldy a mass might well seem hopeless. Tet without this it was debarred from taking its part in a multitude of processes of research to which its powers were wonderfully adapted. Spectroscopic analysis, as applied to the stars, for example, requires the most perfect uniformity of clock-motion, so that the light from a star, once received on the jaws of the slit which forms the entrance into the spectroscope, may not move off them even by a hair's breadth. And the determination of the moon's heat required an equally exact adaptation of the telescope's motion to the apparent movement of the celestial sphere. For so delicate is the inquiry, that the mere heat generated in turning the telescope upon the moon by the ordinary arrangement would have served to mask the result. At enormous cost, and after many difiiculties had been en countered, the Rosse refiector has at length had its powers more than doubled by the addition of the long wanted power of self-motion. And among the first-fruits of the labor thus bestowed upon it, is the solution of the famous problem of determining the moon's heat. The delicate heat-measurer, known as the thermopile, was used in this work, as in Mr. Huggins' experiments for estimating the heat we receive from the stars. The moon's heat, concentrated by the great mirror, was suffered to fall upon the face of the thermopile, and the indications of the needle were carefully watched. A small hut obvious deflection in the direction signifying heat was at once observed, and when the observation had been repeated several times with the same result, no doubt could remain. We actually receive an appreciable proportion of our warmth supply from " the chaste beams of the wat'ry moon." The view which Sir John Herschel had long since formed on the behavior of the fleecy clouds of a summer night under the moon's influence was shown to be as correct as almost all the guesses have been which the two Herschels have ever made. And one of the most interesting of these results which have followed from the inquiry confirms in an equally striking manner anotlier guess which Sir John Herschel had made. By comparing the heat received from the moon with that obtained from several terrestrial sources. Lord Rosse has been led to the conclusion that at the time of full moon the surface of our satellite is raised to a temperature exceeding by more than 380 (Fahrenheit) that of boiling water. Sir John Herschel long since asserted that this-must be so. During the long lunar day, lasting some 300 of-our hours, the sun's rays are poured without intermission upon the lunar surface. No clouds temper the heat, no atmosphere even serves to inter pose any resistance to the continual down-pour of the fierce solar rays. And for about the space of three of our days the sun hangs suspended close to the zenith of the lunar sky, so that if there were inhabitants on our unfortunate satellite, they would be scorched for more than seventy consecutive hours by an almost vertical Sim. There is only one point in Lord Rosse's inquiry which seems doubtful. That we receive heat from the moon he has shown conclusively, and there can be no doubt that a large portion of this heat is radiated from the moon. But there is another mode by which the heat may be sent to us from the moon, and it might be worth while to inquire a little more closely than has yet been done whether the larger share of the heat rendered sensible by the great mirror may not have come in this way. We refer to the moon's power of reflecting heat. It need hardly be said that the reflection and the radiation of heat are very different matters. Let any one hold a burnished metal plate in such a way that the sun's light is reflected towards his face, and he will feel that with the light a considerable amount of heat is refiected. Let him leave the same metal in the sun until it is well warmed, and he will find that the metal is capable of imparting heat to him when it is removed from the sun's rays. This is radiation, and cannot happen unless the metal has been warmed, whereas heat can be reflected from an ice-cold plate. There has been nothing in the experiments conducted by Lord Rosse to show by which of these two processes the moon's heat is principally sent to . us ; nor do we know enough of the constitution of the moon's surface to estimate for ourselves the relative proportions of the heat she reflects and radiates towards us. We do not mention this point from any desire to cavil at the results of one of the most interesting experiments which have recently been carried out. But the recent researches of Zollner upon the light from the planets, have shown how large ly the surfaces of the celestial bodies differ as respects their ' capacity for reflecting and absorbing fight, and there is every reason to infer that similar peculiarities characterize the planet's power of absorbing and reflecting heat. The whole ' question of the heat to which the moon's surface is actually raised by the sun's heat depends upon the nature of that stir-face, and the proportion between its power of absorbing heat or reflecting it away into space. Steeple Jacks. 3 " Steeple Jack" is commonly but erroneously supposed to 1 te an individual,.,whereas, as we have before pointed out, ho , is a genus, or a species, though, it may be, few in number. D As his way of working is not known to every one, the Lon-,- don Builder describes it, in connection with one or two of his e more recent exploits. Some of the factory chimneys at New a Swindon having got out of repair, the company resolved to e employ a " Steeple Jack," who'accordingly made his appear-h at New Swindon and set to work. His plan of proceeding 1, was to fly an Indian kite, with two strings attached The ? ite iees nearly perpendicularly, and wheu above the chim. ney-top is guided over it. The second string is then pulled, and thus a complete communication is formed over the chimney. By means of the string a double copper wire is drawn up, and by this wire some pulleys and tackling. " Steeple Jack " then as -ends hand over hand, and places aa iron band around the chimney, which he secures tightly. Planks are then drawn up and laid upon irons projecting from the band, and thus in a short time a scaifolding sufficient for his purpose is erected, and at a cost very much less than that of a regular builder's. " Jack " had two or three assistants, and managed in his aerial manner, to pull down one of the factory chimneys which had become so badly out of repair as to require rebuilding. He is still engaged in repairing others. His scaffolding looks at a distance like a huge india-rubber band, around the chimney, with ropes depending from it. An exciting occurrence, displaying great intrepidity, and involving the utmost peril to the person concerned, took place lately at Millbank Chemical Works, Garagad-road, Glasgow. Messrs. Burns Son, of Ayr, who have been employed in similar duty at Townhead and other establishments, had ben engaged to point a stalk at the works mentioned, measuring 260 ft. in height, The preliminary process of flying the kite was gone through no fewer than fifteen times, but on each occasion it failed, in consequence of the string being burnt through by the gas and flames emitted from the stalk. About an hour and twenty minutes were spent in these fruitless endeavors, when Mr. Burns, resolving that whatever personal risk migUt Ije incurred, the object must be accomplished, determined for this purpose to ascend the stalk himself. Accordingly, in spite of the remonstrances of his son, he proceeded to mount by the aid of the conducting-rod but no sooner had he got safely at the top than the rope was again burnt through, and he was left hanging by the hands. Not a moment was to be lost. The son flew the kite in about five minutes afterwards, and having succeeded in once more fixing the rope, the father was got down ; he was, however, in an extremely exhausted condition, and notwithstanding the leathern gloves he wore, he was much burned about the hands, while his left side was likewise considerably scorched.
This article was originally published with the title "Heat from the Moon"