From June 16 to August 1 both the upper and lower transits take place during daylight. The azimuth at the time of greatest eastern or western elongation can be easily computed from the formula: sin 4 = sin p where A denotes the azimuth, p the polar distance, and the latitude of the place. DATE OF GREATEST ELONGATION. To find the time of greatest eastern or western elongation, let II denote the hour angle, and/ and p as before, then we shall have This quantity, Hm, added to or subtracted from the time of transit given above, according to the elongation required, will give the mean time of the greatest elongation at any place whose north latitude is 1. Star Table. FOR IDENTIFYING THE PRINCIPAL FIXED STARS. NAME OF STAR. Declination On Meridian. aAndromedie.. Pegasi (Algenib). N 28 31 Cassiopeiæ.. a Arietis. 8 Persei (Algol). aTauri (Aldebaran), Auriga (Capella).. BOrionis (Rigel).. aOrionis (Betelguese). aCanis Majoris (Sirius). aGeminorum (Castor) BGeminorum (Pollux). aCanis Minor.. 1 18.0 +10 40.0 a Leonis (Regulus). N S N 5 296 11.6 +18 9. 6a Pegasi (Markab). 0 I To find the time of the star's transit add or subtract, according to the sign, the numbers in the second column of figures to the date of the transit of the pole star given above. Thus, for a Andromeda February 1. Lower Transit of Polar Star is 4 h. 44 m. 51 8. A M, to which add 10 h. 40 m. and we have 3 h. 24 m. 51 s. P. M.; for December 1, we find 7 h. 26. 56s. P. M., etc. APPROXIMATE PARALLAX AND DISTANCE IN LIGHT-YEARS OF SOME OF THE PRINCIPAL FIXED STARS. By light-years is to be understood the number of years light requires to travel from the star to us. The determination of stellar parallax is one of the most difficult and refined problems in practical or observational astronomy. It is to find the angle which the semi-diameter of the earth's orbit subtends at the star-an angle always very small as seen from the above table and which cannot be measured directly but by various processes too complicated to be explained here. The Source and Maintenance of Solar Energy. (Prepared for THE WORLD ALMANAC by Dr. J. Morrison,) THE solar energy is manifested in part by the radiation of heat and light on which the existence of all animated nature depends. From time immemorial the cause of the solar heat and light has been the subject of study by astronomers and scientists in all lands, and by patient and laborious observations continued for centuries, by profound research and by unremitting toil, man has at last forced nature to yield up to him these hitherto mysterious secrets. A rational explanation of the solar energy was not possible under the old theory of the cause of heat and light-not in fact until the promulgation of the mechanical theory of the former and the undulatory theory of the latter-two scientific achievements of the nineteenth century, a period which will go thundering down the ages as the golden age of scientific discovery and research, In order to obtain a clear idea of the cause of heat and light it is necessary to digress a little to speak briefly of the constitution of matter. Like time and space matter cannot be defined; we know nothing of its intrinsic nature or essence. In a general way, we may say, matter is any substance which occupies space, and exists in three forms, viz.: gaseous, liquid and solid, according to the temperature and pressure. In whatever form it may exist, matter is not a continuous substance, that is to say, it is composed of masses of infinitesimally small portions called molecules, each of which consists of two or more still smaller portions called atoms. The molecules of a body, whether in the gaseous liquid or solid state, are not in absolute contact, but separated from one another by an infinitesimally small space which permits of a certain amount of motion. THE ETHER. This space is filled with that mysterious, invisible, colorless, odorless, and inconceivably rarified substance called ether, which fills all space and holds the universe in its grasp. The molecules of a body are never at rest, but always in motion, and this motion infinitesimal as it is, causes undulations or waves in the ether, and these undulations manifest themselves as heat or light, or both, according to their intensity. Heat and light are thus manifestations of molecular motion propagated by the ether, just like sound, which is a manifestation of undulations or waves of the air. In fact, heat, light and sound are quite similar as regards their mode of production and propagation. Now, as regards the sun, this luminary has been radiating into space a stupendous amount of both heat and light for an inconceivably long period of time, and that, too, without any visible source of supply. Whence then is the origin or source of this prodigious expenditure of energy? Is this radiation of heat and light to continue forever? Does this dissipation of energy imply a waste of the solar substance? Does the solar globe contain within itself the elements of its own decay and death? Stupendous questions are they not? Let us see what answer modern science has to give to them. It is now universally accepted by astronomers and scientists that THE NEBULAR HYPOTHESIS originally propounded by Swendenborg and subsequently accepted by Herschell, Kant, Laplace and other distinguished scholars, mathematicians and astronomers, is the true cosmogony of our solar system. The evidence upon which this hypothesis rests is so strong that it rises almost to the dignity of a demonstration. Without entering into all the numerous details which would render this paper far too long for the space afforded, it must suffice here to say that the gaseous nebulae revealed in the sidereal heavens by the telescope and spectroscope, all the structural and dynamical features of the sun and planets, and the physical structure of the earth and moon, confirm the hypothesis in a most remarkable manner. Indeed, it is hardly possible that so many concurrent circumstances could be the result of chance. All the evidence tends to show that the Creator evolved the solar system by means of the physical laws of matter established by Himself, just as He developed the giant oaks of the forest from the tiny acorns. The nebular hypothesis assumes that the matter composing the sun and planets once existed as a vast gaseous nebula, spiral in form, having an inconceivably high temperature and slowly revolving on an axis passing through its centre of gravity. As the mass cooled by radiating heat into space, contraction of volume with accelerated axial rotation would ensue in accordance with well-known dynamical principles. The centrifugal force thus rapidly increased would cause the separation of large masses, which would, by the mutual attraction of their own particles, gradually assume a spherical figure and become planets. By a repetition of this process planet after planet would be thrown off until the central glowing sun would remain. RESULTS OF SOLAR CONTRACTION. Assuming then, that the sun has attained his present dimensions by the slow contraction of the original gaseous mass, the question which now confronts us is: What amount of contraction or diminution of volume is necessary to supply the quantity of heat and light now radiated? In order to put this in as clear a light as practicable, we will first describe an experiment whose results are quite apparent. Let a large globe of iron, say ten feet or more in diameter, be thoroughly and uniformly heated in a furnace until it has attained a "white heat," or is on the point of melting, during which time it will expand until its diameter be half a foot or more. If it be then taken out and suspended in space it will radiate heat and light in all directions, and, as it cools, it will not only contract in volume, but also give out a light which will gradually change in color from white to dull red, after which the surface will become dark, when heat vibrations only would be manifest. As the cooling proceeds, the surface will contract and compress the semi-molten interior to such a degree that it may crack and the soft material of the interior exude through it. The temperature of the entire mass, with diminution of volume, will continue to decline until it attains the temperature of surrounding objects, when it will cease; but if it were suspended in the inter-planetary, or inter-stellar spaces, where it could not receive any heat from external objects, the cooling and contraction of volume would go on incessantly until the temperature reached the absolute zero point, or, in other words, until all molecular motion ceased. In this condition it would probably fall into dust, the power which hitherto held the molecules together having become dissolved-a condition which may be inferred from the fact that when an iron bar is placed for some time in liquid air or oxygen it becomes as brittle as glass, and yet the temperature of liquid air is far above the absolute zero temperature. The condition of the heated iron globe and the phenomena resulting therefrom are almost precisely similar to those of the sun, which is a huge, gaseous globe, over 866,000 miles in diameter, intensely hot, cooling off very slowly by radiating heat and light in prodigious quantity in all directions, and also slowly contracting under its own gravity, by which a portion of its potential energy is transformed into molecular energy manifested by heat and light. THE THERMAL UNIT. Heat is measured by an arbitrary unit, that is to say, the thermal unit is the amount of heat required to raise one pound of water one degree Fan, in temperature. Carefully conducted experiments show that one square yard of the earth's surface receives about twenty-five thermal units in one second when the sun's rays fall vertically, due allowance being made for atmospheric absorption which may amount to about one-thirtieth of the whole. From the solar parallax, viz 8.81 and the well-known dimensions of the earth we can easily calculate the surface of a sphere having the sun's distance as a radius and hence also the amount of heat received by it in one second or the amount radiated by the sun in that time, and this must be, approximately, at least, equal to the amount generated in same interval by the contraction or shrinkage of the solar mass. The amount of heat generated can be approximately determined by the aid of the mechanical equivalent of heat" which may be expressed thus: If a pound of matter (iron for instance) falls freely through 772 feet it will strike & blow which will raise the temperature of the body struck one thermal unit, or if 772 pounds fall one foot it will do the same thing. Instead, however, of a blow thus struck, a constant and equivalent pressure will produce the same result. By the radiation of heat and consequent contraction of volume, aided by the sun's-gravity, the entire mass is gradually falling toward the centre. By means of all the data now at hand it can be shown mathematically by a process far too abstruse and complicated for insertion here, that a contraction or shortening of about 315 feet annually in the sun's diameter, is sufficient to account for the amount of heat and light at present radiated. This result obtained from the most conservative estimate of all the factors that enter into the computation, must be regarded as an approximation, and it may be a very rough one at that, but however much it may differ from the actual condition of things, a contraction of the sun's volume due to gravity and the radiation of heat, is amply sufficient to account for the source and maintenance of solar energy. THE FUTURE OF THE UNIVERSE. This contraction of volume due to the above causes will of course continue, and a time must come in the far distant future-how many millions of years it is impossible to say--when the sun will cease to radiate sufficient heat and light to maintain animal and vegetable life on the earth, It is certain that all animal and vegetable existences on the earth had a beginning, and it is equally certain that they will have an end. Geology speaks to us out of the rocky strata of the earth's crust, of the extinction of numerous races of animals and plants in the remote past. There have been six grand groups or periods of animated existences on the earth, and five of these have already passed away, and that, too, long before the advent of man. Many of our sedimentary rocks are the solid sarcophagi of countless millions of once living creatures. Our statuary halls and portrait galleries are replete with the memorials of empires and kingdoms, of dynasties and generations of men that have long since passed away. Man himself, nature's greatest paradox, must pass off the stage of his earthly existence and leave to his successors the fruits of his labors and researches. Each day dies and sinks into the silent tomb of night before the next can be born. Every Summer gradually fades away into the cold, dreary Winter before its successor can come forth. The grain of wheat which is cast into the ground, must perish before the new grain can exist. Death thus appears to follow life, pari pass, throughout the entire realm of material creation. To be born, to live and to die, appear to be the destiny of all organized bodies; the tomb of the past is the womb of the future. So, likewise, suns and their systems of planets must die in order that their successors may be born. There is strong evidence of the existence of dark or dead suns in the sidereal heavens. At the rate of contraction just stated the sun will have shrunk to about three-fourths of its present dimensions, in four or five millions of years, and during that long interval its light will gradually change from white, through blue, green, yellow and orange to a dull red and, finally, cast a lurid glare over the dying embers of the solar system. Ages before this animal and vegetable life will have become extinct, and on some rocky crag or frozen knoll the last man may stand shivering in the wintry blasts, and while taking his last, long, lingering look at the universal desolation produced by the appalling calamity which has overtaken the world and overwhelmed his race, he himself will expire "unknelled, uncoffined and unknown." "Sic transit gloria mundi." THE RESTORATION. Such is the logical sequence of the Nebular Hypothesis and such is the fate which awaits the sun and the solar system in the far distant future. There are, however, agencies at work in the sidereal heavens, by which these dead sans and systems may be restored to their original gaseous nebulae, endowed with all their pristine vigor and destined for the formation of new suns and new systems of planets, but space will not permit their discussion now. The solar energy will continue with little or no diminution for perhaps a million of years during which its benign influence will be felt throughout the solar system into which it infuses life, energy and activity. By its genial warmth and marvellous light it clothes our hills and valleys in their glorious garb of green, so pleasing to the eyes, and by the action of its chemical rays of light it gradually changes this same green mantle into the golden tints of Autumn. It paints the maiden's cheeks in their rosy tints and the evening clouds in their gorgeous hues. It sets in motion the gentle zephyr that cools our heated row on a hot Summer day, and it also arouses into activity the hurricane and cyolone which frequently carry death and destruction in their paths. It releases from their icy fetters the tiny streams that trickle down the sides of snow-clad mountains to form the source of the mighty rivers that irrigate our plains and facilitate commerce and international communication. It distills from our oceans and lakes enormous volumes of aqueous vapor which ascend into the atmosphere to form clouds to temper the solar heat, and by the condensation of these clouds to produce the copious showers of rain to purify our atmosphere, to fertilize our fields, to nourish the kindly fruits of the earth for our sustenance, to raise every fainting flower and to revive all animated nature. In remote geologic ages, a portion of the solar energy was stored away in these gigantio forests which ultimately were transformed into beds of coal which we now exhume to warm and light our homes, to propel our ships and locomotives, to drive our mills and factories and to contribute to our comfort in a thousand ways. In short, there is not on the surface of our planet a form of energy which has not been derived directly or indirectly from the glorious orb of day. |