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light by friction, or by the traditional flint snd steel, up to the present time. Lord Bacon in his writings spoke of the process of the smiths of his day in producing light by hammering a small iron rod upon the anvil until itbeoameso heated that when thrust into a bunch of shavings, the shaving* became ignited. It was net, however, said Dr. Paul, till 1798, that Count Bumford, a Scotchman, who had been much engaged in military matters, and particularly in the manufacture of cannon, observed that heat was given off in the process of boring cannon, and succeeded in inventing an apparatus by winch he was enabled to measure the quantity of heat giTen off by a certain amount of work. In 1842, Slayer, a German introduced the term "mechanical equivalent of heat;" and a year later, Joule, of Manchester, made a return of the numerical value of the ratio between hoat and mechanical energy, by which quintitiesof heat could now be expressed in terms of units of work, and in other ways. Dr. Paul then made a few observations relative to the way in which fuel was burnt in the production of steam, and in which tho steam ■waa disposed of, and the results obtained. The application of heat to water for the purpose" of producing steam was daily illustrated by the use of the kettle. Reversing the question, he spoke of the method of taking heat out of water so as to produce ice, a method not used to any great extent in this country. In the boiling of water, tie heat generated by fire was transmitted to the water, raising its temperature to 112 degrees, and then converting the liquid into vapour or steam. Precisely in the same way ice was melted by applying heat to it, and both changes required certain definite amounts of heat. The same quantity of heat that would convert 151b. of wa er from the boiling point into steam would heat SOlb. of water from the freezing to the boiling point, and would melt 1021b. of ice into water, which, efter bring malted, would be at a temperature of 32 degrees. The production of cold was an operation to which attention had lately »een paid, and the nature of the work to oe done was very much the same as that required for producing steam. To produce ice we must take heat ont of water; and the war this must
perpendicularly between the thumb and fore-
a set of individual small pictures, utterly dis-
pencil, will evidently measure c, </, on the land-
.not be far wrong; and tho same rule is ap- method of treating them. First there is the
be done was to find a substance which would an- fpijrable with respect to the foreground. If we perspective to be attended to, by which the upper
BOrb the heat from the water at a temperature at I look at what is close at our feet, it is plain part will curve downwards, the lower part up
trhich ice could be formed. Ammonia, alcohol, J that we cannot at the same time see what is wards; that on a level with the eye will be itself
or ether would do, although the latter would probably be the most suitable. Dr. Paul concluded his lecture by a reference to the other modes now in use for producing ice.
SKETCHING FROM NATURE-IIL TX7HEN a novice first sits down before the "TM scene which he desires to depict upon paper or canvas, his usnal difficulty is to determine how much of the scene he ought to delineate, and how near his own position the picture ought to terminate. He also is usually rather doubtful as to whether the lines of yon cottage roof ought to trad upwards or downwards. In fact, he somewhat resembles the Englishman who, with a fair amount of school French in his head, first set his foot upon continental soil. The language sounds as strange to his ears, and is as incomprehensible, as that of the Ojibbeway Indians, and is not what he expected. The art student, similarly, finds the view before him by no means amenable to the laws of perspective, which he fancied he had understood so well. Never mind; it will all w»» right by-and-by; and as the sketcher gets accustomed to view scenery with tho eve of an •nut, «,e several subjects will fall into their proprr plan., and tl,ere wju bc ,itUe uifficnlry in
softening ftem correctly. Moreover, as the onto-oor practice j9 increased, the indoor theories will become more comprehensible, and errors in drawing- w,l gradually diminish. Remembering always that hoes of really equal height diminish m proportion to their distance from tho eye, there will be little difficulty in ascertaining which way the roofs of houses and similar horizontal hues tend. But there can h0 ,10 question that rt greatly simplifies the task of sketching to rule »line across the drawing at the height of the *T«, and to mark upon it the position of the *3*. <*rf point of view, and also tho vanishing K*nU (if such are needed;. Then hold a pencil
distant; but if we make things at a moderate horizontal. Thus we shall see underneath the
white brick in a half light will tench you much,
treated in a sketch, with tho larger lights on the tipper surface of the layers, beneath which the deepest shadows are generally found. in a finished picture foliage is, of course, much more elaborated; in a sketch from nature, the
aspect is rapidly blotted in or pencilled. Indi-
tree close to
.utsidt sprays that no two
deep shadows between, the upper masses shuttine out the light of the sun from below them, fjtill further off a tree is a mass of gradated, grey shadow, yet етеп then the general form suggests the kind of tree. In buildings, again, details become more and more indistinct as we go further from them. Doors and windows fade into oblong patches of shade (unless the sun ehine brightly upon the glass), yet still there will be always a suggestion, so to speak, of detail. It is a mistake to make the distance always paler than the foreground. Very generally the middle distance is the darkest part of the picture. It is delicacy of treatment, not paleness, that gives distance, and the contrast of »vigorously expressed foreground. Our allotted space is now filled, but it is hoped that even this slight sketch may assist those who intend to devote their spare time in the ensuing summer to the most delightful study possible—a study that always repays our labour B thousand-fold. The writer strongly recommends the brush and sepia as a substitute for pencil or pen and ink, as being, after a little practice, much more manageable, and affording the most rapid method of work, for passing effects of light and shade, such as we specially see on cloudy, threatening days, when menu nary gleams of sunlight flash across the scene, th s medium is perfect. But whether by pen, pencil, or brush, let nature teach, and don't try to teach nature. J. L.
MILBURN AND CO.'S APPARATUS
THE fact that the spent grains from our breweries and distilleries, when properly dried, become a valuable food for horses and all kinds of cattle has been recognised for some time past, although we believe it is only within the last few years that systematic attempts have been made to turn this knowledge to profitable account. The question of desiccating grains has received very careful attention at the hands of Messrs. Milburn and Co., of 76, Chuxoh-lane, Whitechapel, and they claim to have perfected an apparatus which successfully solves the problem they set themselves to work out. A perspective view of the machine is shown at Fig. 1 of our engrav-' ing; Fig. 2 being a vertical section through the feeding apparatus. The dimensions of the machines are about 19ft. in length and Mt. in diameter. A is a fixed cylinder, which consists of two boiler plate shells, the 2in. annular space
between them forming a steam chamber I. B B are revolving shelves, and C is a self-acting screw for feeding the grains from the hopper D into the machine. A connection is made with the steam boiler by means of the pipe E, through which the jacket I is supplied with steam. The condensed steam escapes at F. G is the exit for the dried grains, whilst H is a ventilating flue for carrying off the vapour arising from the grains or other substances being operated upon. The action of the machine is very simple :—The wet grains are fed in through the hopper, and are gradually carried to the other end of the machine by the revolving shelves, where they are delivered dry. The rate at which delivery takes place is of course governed by the degree of dryness required, and is regulated by the working speed of the engine which drives the machine. The degree of heat imparted is also under perfect control. The machines at Messrs. Milburn's weVks are driven by a 10-horee power engine, steam to which—and to the dessicating machines—is supplied from a 40-horse Cornish double-flued boiler, of which there are three at these works. Each of the macliines dries about 100 quarters of grains per week, and from 22 to 23 quarters of wet, produce 1 ton of dry grains.
Another form of this apparatus has just been completed by Messrs. Milburn, who have combined the drying machine with a portable steam engine. This arrangement is seen in perspective at Fig. 3 of our engraving, Fig. 4 being a part cross section and front end view. Here A is the steam space in connection with the water space below; in other words, this is the boiler of the engine. The revolving shelves are seen at B ; С is the flue leading from the furnace to the funnel, and D is the exit for the dried material. The operation of drying is the same as in the machine we have previously described, the difference being only in the construction of the apparatus, the one being fixed and driven by an independent engine, the other being portable and having its driving power attached to it and transported with it. This machine will be found very valuable to agriculturists and others for drying corn, seed, pulse, roots, &c, also for coffee planters and others, and, being mounted on wheels, it can be readily removed from place to place.
THE MECHANIC," a penny publication, which is to-day incorporated with the English Mechanic, gave from week to week a series of " Mechanical Movements," from a useful
little work of that name, compiled by Mr. Henry J. Brown, the editor of The American Artisan. We (-hall so far follow in the footsteps of the absorbed penny journal as to take weekly from the same source a few specimens of its illustrations and descriptions.
1. A mode of obtaining an egg-shaped elliptical movement.
2. A movement used in silk machinery to guide the silk on to spools or bobbins. On the back of a disc or bevel-gear is secured a screw with a tappet-wheel at one extremity. On each revolution of the disc the tappet-wheel comes in contact with a pin or tappet, and thus receives an intermittent rotary movement. A wrist secured to a nut on the screw enters and works in a slotted bar at the end of the rod which guides the silk on the bobbins. Each revolution of the disc varies the length of stroke of the guide-rod, as the tappet wheel on the end of the screw turns the screw with it, and the position of the nut on the screw is therefore changed.
3. Carpenters' bench-clamp. By pushing the clamp between the jaws they are made to turn on the screws and clamp the sides.
4. A means of giving one complete revolution to the crank of an engine to each stroke of the piston.
ß and 6. Contrivance for uncoupling engines. The wrist which is fixed on one arm of the crank (not shown) will communicate motion to the arm of the crank which is represented, when the ring on the latter has its slot in the position shown in 5. But when the ring is turned to bring the slot in the position shown in G, the wrist passes through the slot without turning the crank to which the said ring is attached.
7. Contrivance for varying the speed of the slide carrying the cutting tool in slotting and shaping machines, k.c The driving-shaft works through an opening in a fixed disc, in which is a circular slot. At the end of the said shaft is a slotted crank. A slide fits in the slot of the crank and in the circu ar slots and to the outward extremity of this slide is attached the connectingrod which works the slide carrying the cutting tool. When thedliving-shaft rotates the crank is carried round, and the slide carrying theend of the connecting-rod is guided by the circular slot, which is placed eccentrically to the shaft; therefore, as the slide approaches the bottom, the length of the crank is shortened, and the speed of the connecting-rod is diminished.
8. Keversing-gcar for a single engine. On raising the eccentric-rod the valve-spindle is released. The engine can then be reversed b working the upright lever, after which the eccentric-rod is let down again. The eccentric in this
jection on the shaft acting upon a nearly semicircular projection on the Bide of the eccentric, ■which permits the eccentric to turn half-way round on the shaft on reversing the valves.
9. This enly differs from 3 in being composed of. a single pivolcd clamp operating iu connection with a fixed side-piece.
10 aud 11. Diagonal catch or hand-gear used in large blowing and pumping engines. In 181 , the lower steam-valve and upper eduction-valve are open, while the upper steam-valve and lower j edoction-valve are shut ; consequently the piston will he ascending. In the ascent of the pistonrod the lower handle will be struck by the projecting tappet, and, being raised, will become engaged by the catch and shut the apper eduction and lower steam valves; at the fame time, the npper handle being disengaged from the catch, the back weight will pull the handle up and open the upper oteam and lower eduction-valvca, when the piston will consequently descend. 11 represents the position of the catchers and handles when the piston is at the top of the cj Under. In going do»n, the tappet of the piston-rod strikes the upper handle and throws the catches and handles to the position shown in 10.
partially <pcned, and are quickly closed again, to that the admission of steam ceases Borne time before the termination of the stroke, and the steam is worked expansively. The nearer the slide is to the middle of the slot the greater will be the expansion, and vice rerta. (To be continued.)
I THE EAR.—ITS USES AND ABUSES.
14. Link-motion valve-gear of a locomotive. Two eccentrics are used for one valve, one for the forward and the other for the backward movement of the engine. The extremities of the eccentric-rods are joined to a curved slotted bar, or, as it is termed, a link, which can be raised or lowered by an arrangement of levers terminating in a handle, as shown. In the slot of the link is a slide and pin connected with an arrangement of levers terminating at the valvestem. The link, in moving with the action of the eccentrics, carries with it the slide, and thence motion is communicated to the valve. Suppose the link raised so that the slide is in the middle, then the link will oscillate on the pin of the tlide, and consequently the valve will be at «»t. If the link is moved so that the slido is at one of iu extremities, the whole throw of the eccentric connected with that extremity will be given to it, and the valve and steam-ports will be opened to the full, and it will only be toward the end of vhe stroke that they will be totally shut, consequently the steam will have been admitted to the cylinder during almost the entire length of each stroke. But if the slide is between the middle and the extremity of the slot, as shown in the figure, it receives only a part of the throw of
The blind man, who, from his birth, has been deprived of the sense of the beautiful, who sees "men as trees walking;" the deaf mute who can never take in the beauty of song, are lightly Bmitten compared with th"se who are suddenly bereft of these luxuries of life ; they will hardly adopt Pope's saying, that "whatever is, is best." Can wo read the history of Beethoven's crushing calamity of deafness, stealthy in its approaches as the heavily-laden thunder-cloud, without feeling the deepest sympathy for that will-impassioned nature, weird-like in ita grandeur, fierce, uncouth, rendered all the more taciturn by the master malady of his life, denied tho full enjoyment of tho very wonders he created, poor, independent, high-sonled, he seemed at last to wrap himself within himself, preferring gloom and solitude, to such friendships as were worlh his acceptance?
Forgotten at Vienna, where he is now adored, he died without the worldly consolations, Coleridge has so happily touched, and quaintly expressed, in the following lines :— Tho' frlendshtpB differ, endless in degree. The sorts,methinks, may be reduced to three: Acquaintance many, and conqualntance few, But for /nqualntance I know only two. The friend I've mourned with and the maid I woo. These were written on the occasion of seeing his
little daughter in company with another child. "Who may your friend be?" asked the father. "She is 8n ('(tqnaintanco ef mine." Poor Beethoven ! You might have floodod tho world with the fruits of your unrivalled genius if woman's tender suasion had drawn you out of yourself and leftyou untrammelled by your galling kindred. Deafness to tho musician, or blindness to the painter, who can say whioli is the more dire calamity? Signposts on the way to decrepitude; slackenings of Bpced that tell of sands nigh ruu out; warning chimes of a fast-fleeting three score years and ten—perhaps, a long way on this side the mark. We hear with the keenness of childhood, we feast in olfaction the glories of tho summer flower-garden freshened by a passing shower, bnt as we advance in life we find things are not what they were, pleasures are grasped and gone—the flowers arc the same, the brightness of the glowing sun is aone the less, the lovely quiet of a summer's eve, with its schoolboy reminiscences—a far back vista—is brought from memory's treasure-house; friends gone from onr very embrace arc present in imagination, and change impresses its finger on all things. Why si ould it not? There is nothing perfect here. Some of us are born with decay ready imprinted, a tiny spark it may be, but soon fanned into giant dimensions, the unexpanded bud is nipped, and on all iB inscribed decay. How often comes the expre-sion, with a sigh, "I [cannot do what I used " 1 No, my friends, we once could go hand-over-hand tho five-barred gate ; that no longer suits us; Eolid thews and sinewB are useful but not lithesome; we now feel that we have organs that we must tiFe with deference if they are to be lasting, alihough time was, I daresay, when you and I considered •' a stomach " a myth, or, at best, the semblance of a reality capable of accommodating anything short of paving-stones—but pain is a reminder, physic is u. reminder—notably that horrid chief remembranci r, ' Gregory's Powder," which chemists call a '• KhabarbHrato of Magnesia"—barbarous enough in any senso, looking like a compound of crabs' claws prepared by loving bands, and from which es' ape was impossible, for if your si nse caused you to eject the unsavoury morsel through yonr nose into the cup or giver's face, a double portion in the morning was "your shepherd's warning." This was a reminder that your future jonrney through life was to be crossed by nps and downs—troubles as plentiful as the sparks that fly upwards. What has all this to do with our senses and privileges? TMucn_> I opine, considering that the better you use the the longer you will enjoy them. My labours,
truBt, have not been in vain in my endeavour to tighten your eyes, and it will not be my fault if I fail to enlist your attentive ears. I trust Wisdom's proclamation will not be lost on you when she Bays, •' This is the way; walk ye in it, tvhen ye turn to the right hand or to the left."
The sensation is most pleasurable when a ship is in full sail, and one pair of hands can control the wheel. The compass before you, the course there indicated, and your eye ever and anon turned to the well-tilled canvas, tells you all is right. The tall masts bend, and you feel her give as she flies through the water; but throw her out of her course, and as the bellying canvas flaps against the mast, you are conscious of loss of progress. Again you return to your missed point, and the breezes favour you. So I must take my course right ahead, and try and avoid a long tack.
Man, being the highest of creation, has everything for his wants fashioned in the highest perfection, " a place for everything, and everything in its proper place," saves his ideas, and these tenements of his brain be occasionally lets out to queer lodgers. We will follow the same division here as in the former paper on "The Eye," consKleringfirst thccxternnJ, then the inner or true ear; but first look at the temporal bone of the skull, calh d so because "Old Time," or Tempus, left his grey hairs thereon as a set-off against the bald vertex. In that triangular-looking portion which is the hardest in the body, was once the perfect hearing ear, there are pome odd holes or so in it that used to puzzle us students when we had nothing better to do than load oar brains with hard names, and devious courses of nerves, what they were related to, and what not, and what, I am rejoiced to 6ay, I have long since forgotten, names invented to frighten one, as I thought when I came across the "mylohyoidean branch of the inferior dental of the fifth pair." Pity they didn't add some more! Now, this earbone contains an anatomical nnt, one of the wonders of the body, seldom broken into unless a terrible fracture of tho skull shatters it. The eye was placed in the front of the body, the van, as it were, the ear, as sentinel, does duty in the rear, nnhapplily no protection against those who talk behind your back disiillingmalice. We can afford, however, to pass on, as did He "who wrote on the ground as though he heard them not." Would that our grievances were always thus recorded, to be effaced by the next passer by!
A pretty ear is one of the special ornaments —may I say vanities?—of the ladies, highly prized. To be'deprived of it was a mark of infamy. To be nailed by the ear to the pump was not a pleasant process, and a durance vile with a vengeance. Earrings are nowadays as common as earwigs, an amiable weakness with women (affected sometimes by male Yankees, and others, under the delusion that they cure sore eyes, which they don't), but a graceful appendage, I must say, to the more'graceful ear, common to all nations, and in this country to all classes. You see light and heavy weights, false and real gems, adorning the ear, but the beauty is in the soft, cushiony lobe, that feels clastic to the fingers—a privilege reserved for you when you are " over head and ears in love," unless you are one of those who elongate the ears of youngsters as a corrective to evil manners, a custom, let us hope, falling into desuetude, a process that did convert the "silk purse into the Bow'm ear," and in the days of our grown bullies at school I have known boys to he thus elevated by the monster dunces that infested our Dothoboys Halls. Some jewellers,sensible of the beauty of the lobe, do not pierce it, but encircle it with a gold wire, a mere trifling addition to the pleasure of supplying the pendants. The piercing of the cars may lead to troublescsme inflammation or eruptions, as I have many times seen. Some think that the allusion of the Psalmist, "Mine ears hast thou opened," or bored, refers to the practice of boring an awl into the lobe (Dcut. xx., verse 17), the master by that proceeding making "a servant for ever." It is a practice in the West Indies (" Wilde on the Ear") for a negro, when he wishes to attach a dog to him, to nail his ear to a door-post for the period of one day—rather R novel mode of proceeding, to say the least of it.
The car stands out a little from the head to catch the sounds, and the hollow cup, or concha (shell), acts as an car-trumpet; the outer rims are called respectively the helix (j\<£) or fold, and the antihelix, peaked portion in front, is denominated (betragos (.rnayoc), the hairs on which are supposed to resemble a goat's beard. These, with
the auricle, or external car, so far as you might slice it off. The passage t i the ear, or auditory passage, is partly formed of cartilage, as is the car proper, and this is attached to a bony canal pretty firmly. Blood is not sent in very extravagant supply to the ear. savein tho very amiable
woven habitations crowds of spiders, which formed a circle about him while he continued playing on his instrument. At first he was petrified with astonishment, when, having ceased to play, the assembly of animals immediately broke up. Having a great dislike to vermin, it was two
and tell-tale process of blushing (a nervous act), days before he ventured to touch the instrument,
but having mustered courage to conquer his dislike, he recommenced his concert, when the assembly was far more numerous than at first, and in the course of time he found himself surrounded by a hundred of these musical amateurs. M. Marville observed, while a man was playing on a conch shell, that a cat was not in the least affected, and he even judged by her air that she would have given all the musical instruments in the world for a mouse, for she slept all the while unmoved in the sun ; the horse stopped for a short while before the window, raisiug his head up now and then as he woe feeding on the grass; the dog continued for above an hour seated on his hind legs looking steadfastly at the player; and the ass did not discover tho least indication of his being touched, eating his thistles very peacefully ; the hind lifted up her large white ears and seemed very attentive ; the cows slept a little, and after gazing awhile went forward; some little birds who were in an aviary almost tore their little throats with singing; but the cock minding his hens, and the hens solely employed in scraping a neighbouring dunghill, did not show in any manner that they took the least pleasure in hearing the music."
(To be continued.)
and by no means the tell-tale process it is supposed to be—although sometimes a charming thermometer of the thoughts—albeit a gentle suffusion, but acceptable to some eyes as the roseate blush of morn to the expectant shepherd.
It used to be said when your left ear was red somebody spoke well of you—that I can't be certain of ; but when both ears suddenly redden you may set it down, on my authority, that the parties have not paid their doctor's bill. Why one ear should be hot to tingling and the other quiescent, is one of those things we have yet to learn, unless it be that one carotid artery is larger than the other, and this may account for the common fact that one whisker is smaller than the other. Special muscles are attached to the ear which cause it to raise itself when any special message is telegraphed—not under post-office surveillance. Some people can move the ear upwards and downwards. I am favoured with that addition to my accomplishments. When the ear is outstretched, increased hearing is the result. Look at the sharp terrier, how movable his auricles are; how he fixes them forward when he smells a rat, and, with forcpaws outstretched, is ready for a spring. Watch the activity of the ear in the graceful greyhound; or observe the cavalry charger with outstretched ear patient for the call to arms, eyes intent, nostrils dilated, muscles in impatient quiver, as if horse and rider were all one. When I had the misfortune to be a parish doctor, drawing the munificent stipend of £G0 per annum, more or less, and obliged to keep a horse to do the work, I used to talk to my horse as I went along, and watch his ears moving as if he understood me, and the poor beast evinced his gratitude for kindly care far more so than some of the patients. He,as a goodly Houi.ynh>m, appreciated my kindly qualities, except when I passed a ball down his throat, and patted him into an appreciation of the bolus. If the power of speech had not been denied to him, he would surely have exclaimed, "Save me from my friends!" Would that we were always as ready to the call of duty as those dumb creatures, and ever grateful! The elephant has a lazy, comfortable-looking ear, tapering in its point, »s if nature intended it as a whip for adventuresome flies j and we must not overlook the dear, old patient donkey, patient even to the burthen of the fat Brightonese ladies, done up in hats and feathers, chignons and panniers. No wonder the poet should exclaim :—
Poor little foal of an oppressed race,
The animal begets its kind care and thanks to the society for its protection. We seldom see the beast of burthen bludgeoned as in days gone by, or assailed with the Bavagcry of a Balaam.
Fish moving quickly through the water, or birds with the speed of an arrow II nig through the air, would be only encumbered with an external auricle, and with them it is dispensed with. Both fish aud bird hear acutely enough, remarkably so the former.
Not to go back to the story of Amphion and the Dolphin, or to the music-loving propensities of the seals, described by Sir Walter Scot (" Lib. Eut. Kuow.") as—
Rude Heiskar's seals, through surges dark,
'■' In Germany they take the shad by means of nets, to which bows of wood, hung with a number of little bells, are attached in such a manner as to chime in harmony when the hells are moved. The shad, when once attracted within the sound, will not attempt to escape while the bells continue to ring. Aelinn gays the shad are allured by Castanet", and so delicate is the ear of the fish reported to be, that the sound ol thunder terrifies them to death, and numbers are annually found thus killed on the Rhine and Moselle." Butto cite other cases of acute hearing in birds, &C. :—"An officer confined in the Bastille of Paris begged the governor to permit him the use of his lute to soften his confinement by the harmonies of his instrument. At the end of a few days this modern Orpheus, playing on his lute, was greatly astonished to see frisking out of their holes great
THE EARTH- ITS FIGUItE AND
By Richard A. Pboctob, B.A., F.B.A.S.,
Author of " Saturn and its System," "Sunviews of the Earth," lie, &c.
CHAPTER W.-- (Continued.)
The Earth's Revolution.
BRADLEY'S discovery of the aberration of the fixed stars forms one of the most interesting narratives in the whole range of the history of astronomy. Yet, here I must perforce leave it untouched, and deal only with the phenomenon itself, since properly to relate the steps by which he was guided to that most important discovery, would occupy all the rest of the space now available to me.
The great and general law, then, to which the apparent annual motions of the stars are subjected-^ law which must be accounted for by any theory which pretends to exhibit the real relations of the celestial bodies—is this: Every Btar in the heavens, whether obvious to the naked eye or visible only by tho aid of powerful telescopes, whether shining in solitary splendour or lost, so to speak, in the profundities of some rich star-cluster, travels once a year in a minute ellipse, whose major axis is somewhat more than two-thirds of an arc-minute in length, while its minor axis depends on the position of the star with reference to that great circle on the heavens in which the sun seems annually to travel. A star close by the pole of this circle—the ecliptic —has an almost circular aberration-ellipse; one near the ecliptic itself has an aberration-ellipse so eccentric as to be almost a straight line. But every star has an aberration-ellipse of the same major axis. And that major axis, though, as I have said, minute, belongs to the order of magnitudes which are obvious to the telescopist—palpable, unmistakable, clear as the sun at noon to the worker in a well-appointed observatory.*
Now let us inquire what the particular law is according to which these remarkable ellipses are described by the stars, for much depends on this point. If merely a vague notion is given of the character of this instructive phenomenon, then some vague and general explanations will immediately suggest themselves to the supporters of paradox. When the exact nature of aberration is described, the proof of the earth's revolution
the antitragos, opposite the tragos, complete numbers of mice, and descending from their
*The mere fact that Bradley, when telescopic appliances were so imperfect, at once recognised the aberrations of the first tixed star he watcher) with care, though he had no reason to look for or expect such a motiou, is enough to show how very palpable the phenomenon 1b. But it may be well to add that astronomers can now rrcogulse aud feel certain about stellar displacements which are only about one-hundrtdth of the aberration motion.
eooogk not to pretend blindness), absolutely irrefragible.
The beet way of describing the nature of aberration is by a reference to the accepted theory of tie earth's motion. Let 1,2,3,4,Fig.l,represent the earth'« path (perspectively presented) around the son, and suppose a «tar so placed on the heavens aa to occupy the pole of the ecliptic; then the star being at a distance practically infinite, we should expect the lines of eight from all the points in 1, 2, 3, 4, to the star, to be directed toward« this point—the ecliptic pole. In other words, the lines IS, 2S, 3S, 4S, would all be at right ingles to the plane 1,2, 3,4. Instead of this, wiea the earth is at 1, the star is seen toward* Si, the plane SI *' passing through the taagtnc line to 1, 2, 3, 4, at 1. So when the earth is и 2, the star is seen towards s>, the plane S2 J? passing through the tingent to the circle 1, 3. 3, 4, at 2. And similarly when the earth Ь at 3 or 4, the star is apparently displaced as •down, the displacement being always an angle of one-third of a mioute (approximate ly),and always in the direction of the earth's motion. Next «oppose the star placed on the ecliptic. Then the earth's p'itU being again represented by 1, 2, 3, 4, and the lin«» IS, 2S, SS.4S, being drawn
in that plane parallel to each other to indicate the direction in whi. h one would expect to sec «he »tar, it is found that, wherea* when the earth bat 1 and 3, where she is moving in a line towards or from the star,there is oo displacement; when she is at 2 and 4, where she is moving at right angles to the line of sight to the star, there is the «ame displacement as in the former case. Aim, is this second cuse, the star seem* more and more displaced as the earh travt-ls from 1 to 2, then le<5 ¡md less till the earth is at 3, when there is no displacerá, nt; then more and more, but on the contrary side, till the enría is at 4, and ЯО finally fen and Ь-ee till the earth is again at 1. It will be easily >ecn that in the first caso the star appears to describe a circle 1. 2, 3, 4, Fig. 3, ahont its mean po-iti..n S, while in the latter it describes a »traigbliue 1, 2, 3, 4, Fig. 4, through its mean position S; 2, 4 in Fig. 4 being equal to the diameter of the circle 1, 2, 3,4, in Fig. 3.
have made use of the accepted theory to describe the observed motions, this by no means involves the assumption that the accepted theory is correct. It it the fact, and a striking fact it is, that we cannot even describe stellar aberration conveniently without a reference to the accepted theory, so that even though that theory were false, it would still be convenient to speak of the aberrations of the stars, as being snch as would correspond to such and such assumptions respecting terrestrial motion.
Bnt here we hive a phenomenon to explain. We have every star on the heavens announcing some great fact to us, or rather writing down year by year on the celestial concave a lesson for our instruction. To reject the lesson as meaningless, would be to abandon one of the highest and noblest faculties given to man, his desire to search out and investigate the problems set by nature for his interpretation. What, theD, is the meaning of this million-on-million-fold repeated lesson? Can as'ronomers explain the matter? Perhaps astronomers have some far-fetched explanation, which they would force on the world by crafty argument
The case is otherwise. Astronomy can not only interpret the aberration motions of all the millions of stars revealed by the telescope, but the accepted theory of astronomy would have to be abandoned if those motions did not take place. Stellar aberration was discovered as by an accident, was long looked ou as a great s inrce of doubt and perplexity, was honest y submitted by astronomers to the inquiry of the world—and then suddenly it was seen that the aberration motions could not but take place, if the earth moves as the accepted theory asserts. Let us inquire how this is.
It had been independently discovered, by observations made on the eclipses of Jupiter's satellites, that light travels with finite, though inconceivable velocity. Always when Jupiter- and his family were farthest from the earth, the satellites seemed tardiest to announce by appearance or by disappearance, their motion through the shadow of their priman-. And so it was seen th it the light тев-ацез sweeping to us from these bodies come at a definite speed to the earth. A consequence of this peculiarity hud been wholly overlooked by astronomers. The light travelling in appreciably parallel lines from a star towards the solar system, may be compared to a shower falling in parallel lines on moving bodies. Now we know that in moving through a vertical shower of rain, the rain seems to fall somewhat towards the face. The reason is obvious ; thus, suppo-e a traveller's face at 1, Fig. 6, when a a rain drop is at Ri, and that l.y the timo he reaches 2, the rain drop is at ll2, it is clear that the drop will seem to have fallen from a position in front of him, and in the direction indicated by the dotted lins; and if we conceive of the motion of a small body travelling in a circle under a vertical shower, we shall see at once that this property may be made to illustrate every case of etellar aberration, by assuming different positions, as 1, 2,3, in Fig. 7, for the circle iu which the body moves under the shower.
It will be seen, though, that in order that this explanation may hold, it is necessary that the rate of motion of the earth should Ьелг an appreciable relation to the enormous velocity of light. It raiu fell a thousand times as fast as it actually does, the fastest runner would not find that a vertical rain-shower would seem to fall appreciably towards his face. Now, apart from all considerations of the real sir.e of the earth's orbit, or of the rates of motion cither of light or of the earlli in her orbit, we can at once test this explanation of aberration. It had been independently shown by Römer that light takes about eight minutes in crossing the radius of the earth's orbit; the earth occupies a year in travelling rouud the circumference of the circle; all we want to know if, whether the displacement of a star over an arc of about one-third of a minute, corresponds to these re ations. What we require is, that supposing 3. V.°- to be the distance traversed by light in any time, E1 E2 the distance traversed by the earth in the same true, S1 V,2 K1 being a right, angle, tho angle E1 S Ea should be Uuuul one-third of a minute of arc. Let it be re
before it had been guessed what a noble proof of the true theory of astronomy was to be adduced from it. Now for the test of figures. Since the earth completes a circnit ofherorbi in one year, she would traverse a length equal to the radius in the period 365 X 24 X GO
2tt where ir represents the number 314159.. . or the ratio of a circle's circumference to its diameter. Hence the velooitv of light is to that of the earth 365 X 24 X 60
as -. 8 ; or as S2850 : v. Now
2tt the proportion of E,, S to E| E, where Ei S E» is an angle of about oue-tbird of a minute of arc is
1: or 32400 : T. It is seen then,
360 X 60 X 3 at once, that we have a satisfactory explanation even with these rough assumptions, since the
1 difference between 32400 and 32850 is bnt —nd
72 part of 32400. Bnt if I had taken the mean of the estimates of the volocity of light from observations made on Jupiter's eclipses, as determined before Biadley's observation, and Bradley's estimate of tbe aberration of the star y Draconis as made before he knew what theory required, the coincidence would have been fouud very much closer.
Here, then, we have a perfect proof of the earth's revolution. No question can remain that the lesson really taught us by the stars as thoy annually traverse their aberration ellipses is this, that the earth annually traverses a nearly circular path round the sun. This interpretation accounts for all the peculiarities of the stellar aberration motions; nay, the theory of the earth's motXon requires every one of those peculiarities. No other theory has ever been put forward in explanation of stellar aberration,* and it may be'alleged, with more than confidence, with the fullest certainty of conviction, that no other theor сип. explain.
CHAPTER VII. The Earth's Motion As As Attendant On
The Sun In His Jouuney Through Space.
Since the stars are observed to be slowly shifting their positions on the celestial vault, and therefore presumably in space, it is obviously suggested that the sun, which is but a member of the sidereal family, has also his proper motion through space. It is a difficult problem to determine what that motion is, because all we have to
* I need take uo further notice of a so-called explanation in a work puroorting to be written by a Cambridge wrangler (annie not given), than to remark that it docs not even pretend to explain details, and that what it does pretend to do suffices to exhibit the utter ignorance ot the writer as to tlie real aaturo of the problem. I do not say that the writer is not a Cainbridge wransrler, because I know from my own rxperieuce tkac n man may become a wrangler without knowing even the definitions of astronomy. But I do say that the writer, being a wraKgler, should have had sense cuou^h to know that before pretending to write on ustrouomy, he ought to have acquired a bettet knowledge of the subject tbau he Mjows.nimeelf to have.