Show uk 91 T V D li firn I 1 i u C 1 j i etc i r i fl t fatt r wi rt iti sti i in f astronomy iri f BY PROF ORSON bratty seh SEL 41 i 1 I t q ai TI rEO meo i astronomical science i defined viewed in il all a lf ages with tac the mot profound in berest terest copernicus kepler and neta oon fon rhe tae warth as an astronomical body 0 d 1 kure kurc mure jeow jiow ais jis its dimensions how hom how demonstrated its position in space up and down obil only ie lativs relative I 1 term lems owr owr antipodes r fi zurnal A alpar L en cm tf notation rotation of the starry 1 1 sp he re rotation of the earn eara demonstrated 6 rated on mechanical principles aila also denho derho demonstrated nitrated by falling bodies asiro asino is that science which treats of the figures magnitudes distances motions relative positions appearances and physical constitutions of the great bodies which compose comm corn pose poso the visible b universe universo s e or in other words it is that department of science which has for its object to investigate the phenomena of worlds which exist in countless numbers in the immensity of space it is that science which lifts the veil of obscurity and exhibits the grand scenery of the universe as it existed in ages past as it now exists and if not interfered wit with by causes unknown as it will exist in ages to come it ia that science which above all others is calculated to give us the most profound pro pru found sublime and exalted views of ot the power wisdom and goodness of that being who formed those magnificent systems from the eternal elements and devised laws calculated to maintain their stability rugh through th all their complicated and infinite variety of movements for indefinite ages to come this is a science which has engaged the attention of individuals nations and generations erat ions from the earliest period of man for what rational beins being can look upward into the blue vault of heaven and behold the sun in its enn eff effulgent fulgent glory the moon shining with a silvery brightness exhibiting its ever varying changes the stars be spangling the vast concave of a nocturnal sky twinkling as it were with joy and lighting up the dark unfathomable abyss of an unknown immensity what rational being we again enquire can behold this august and sublime scenery without feeling the thel most intense desira to unlock the heavenly archives and read from the great book of creation the grand science of the origin of worlds the laws by which they are governed and their eternal destinies kings rings upon their thrones and the humble shepherd in the field have alke participated in this sublime emotion the poet enraptured with the mag wag ant glories of the heavens has poured forth his sublime st ef effa fusions in the most melting harmonious strains of glowing eloquence while the man of god with loftier views and higher aspirations has soared aloft from nature up to natures author and overpowered with the infinite greatness and resplendent glories which surround himo him on n every side he be bows in humble adoration before the areat great eternal and exclaims what is man that thou art mindful of him or the son of man that thou test him I 1 this sublime science is said to have been cultivated in the earliest ages by the antediluvian patriarchs p also by the Chal deans and egy egyptians I 1 a faw few centuries after the flood an and d by many from the days of moses until chr christ is t passing over many distinguished and celebrated astronomers of ancient times we merely observe that during the dark ages ignorance usurped ibs iff dominion over the mind of man and the light of an ancient clent astronomy became nearly extinguish extinguished edd eff from the horld world the earth was assumed to be th e stationary centre of the universe around which the sun moon and stars staret were said to perform their revolutions revelations JG go cycles and epicycles were In invented Tented to for the irregular motions among the planets and the whole system of as became encumbered with absurd aties invented to upheld the false theories of pt and aristotle which held for many generations an almost universal sway over the mind of man copernicus at the beginning of the six century brolle through in a meas olieas ure ure ore the superstition and ignorance of his predecessors by transferring trans fering the centre of the planetary system from the earth to the sun and thus forming the heliocentric hello centric theory to account for the phenomena observed kepler nearly a century afterwards discovered the elliptical theory of the planets and overturned the favorit favorite 0 hypothesis of circular orbits which had up to that time been universally received ile he also discovered the law of motion in elliptical orbits and unfolded the relation existing between times and distances these grand improvements in the sei sel e n c of astronomy laid the foundation for th the ii e great t discoveries of the immortal newton to who revealed to the astonished nations as t that hat great law of universal gravitation or the law of force lorce by which the great bodies of the universe are bound together in their respective orbits during daring the last century and a half the newtonian system has been studied with unwearied diligence and astronomy has been rescued from the errors and absurdities of the dark ages and established upon the firm foundation of mathematical certainty which can never be overthrown it is the newtonian system which we shall endeavor to ill lil illustrate in the present series serles of lectures and to which we earnestly solicit your undivided attention we shall commence oom mence mente with an examination of the earth as one of the constituents of the solar system and as the planet with which we are more immediately connected and as the station from which all the others are seen if we form lorm erroneous opinions in relation to the earth the same errors will be interwoven in a greater or less degree with all our oar notions concerning the other bodies of the system if we suppose the earth darth to be a flat extended plane the phenomena ph e exhibited in the heavens as seen spen from different points of its surface would be inexplicable if we suppose it to be stationery the motions observed among the heavenly bodies can no longer be con soldered as apparent arising from irom the motion of the earth but as the real motions of the bodies themselves many of which would appear inconceivably str strange auge ange if not absolutely absurd being su subject abject to no regular law of order which characterizes other phenomena with which we are acquainted quain ted if the rising generation among these mountains were to grow up without any instruction in regard to the form magnitude and motions of the earth only what they should gain gala by their own observations their first 1 impression would be that the earth is a alid kind hind of concave valley bounded by mountains on every side but after an oi exploration 0 of nifty fifty t or a hundred miles their views would be somewhat enlarged they would now consider the surface of the earth a succession of hills and valleys delineated upon a comparatively flat plane all ideas concerning the extent or thickness of this plane would be exceedingly vague and uncertain some might suppose it to be limited by an awful precipice extending down through the infinite depths of space others might suppose the earth itself an infinitely extended plane piano without boundaries in any direction except its upper surface we will now suppose that an exploring company should be selected and fitted out to explore the earth in an eastern direction when they had travelled duease due du east easu easu east between seventeen and eighteen thousand thou saud sand miles alternately over land andrea and sea what would be their astonishment at finding themselves just entering the valley of the great salt lake on the west they would scarcely be believe belleve eve the evidences of their senses the only just conclusion they could form in relation to so strange a phenomenon would be that the earth was wag roundal roun dat least from east to west but a question would immediately arise among them whether the earth was round or convex in all directions like a ball or whether it might not be of a cylindrical form like a saw log or like a steam engine boiler used on our railroads they might suppose it to toi be convex from east to west but straight or flat from north to south this question could be decided in the following manner if wo we stand on the deck of if a ship at ac sea when out of bight 0 f we wd should be able to see hundreds of miles in all directions if the surface of the ocean were a level plain indeed were our view not obstructed by mists fogs or clouds we be able to see hundreds of miles large continents and islands thousands of miles in the distance would be rendered visible observation shows this wot riot to be the case but we find in every direction from our station a clear an dwell acdwell and well weli defined boundary anly 6 a few mi lesin the distance As ships fass bass pass over this ebis boundary we gradually lose sight of them the hull huil disappearing disa e ir first then the lower jower ower sails and finast finally the top sails salis seem seam to hink sink butof out of sight as thoy they recede in the dist distance adee aften aen after they have lave thus disappear disappeared edi odi the most powerful telescopes will not render them visible but by y ascending to the mast head they B seem eora een eor a gradually to rise again agila above the horizon and ard aro distinctly visible to the naked eye ye which clearly demonstrates that it is not owing dwing to any incapacity of the organs of vision to see further but that the con convexity of the th a water intervenes between the eye and the object and thus thu hid hides esit it fro fram from our view since the same effects are observed from every part of the ocean and in every pos sible direction north and soula south as well weil weil well as east and west it follow that the same same convexity must pre prevail ail all on oil o n every side and therefore that the tha earth cann cannot ottoo be of a cylindrical indr ical leal form but must be round rou ad like a globe glober an another ather demonstrative proof th that atthe the earth is a globe is given by y considering the form of the earth rf shadow when it falls upon the surface of the moon during a lunar eclipse when xhu 9 moon passes pass es dire dine directly etly behind the earth so aa as to forni foroi a straight line with the earth and sun the shadow of the earth extending in a direction opposite to the sun will fall upon the moon and will at atall stall all ail times appear cir circular ediar edlar upon the moons disc if the earth were considered stationary and if a lunar eclipse should always happen at the same hour of the night this would be considered is factory y evidence evi evl denice derice of the globular figure for there ther are many daany bodies besides a globe which will in certain positions cast a circular shadow A grindstone a sugar loaf or even a gogof wood when held with its circular end facing a light will form a circular shadow in the opposite direction now in order to determine the true figure of either of these bodies from its shadow let lot different sides alternately face the light and we shall soon be able to declare its true figure with mathematical certainty let different sides of the earth be presented towards the sun I 1 and if the shadow still continues to be circular i we know the earth must be a globe for no other figure is capable of producing a circular shadow when its different sides are exposed to the sun in a variety of positions for instance if a lunar ellipse were to happen at siw six in the evening about the first of january and another should happen at some future period about the same time lime of year but at twelve at night then the side of the earth presented to the sun during the former of these eclipses cit ses would bs ba at right angles to the side presented during the latter yet in both instances its shadow upon the moon would be circular this then is a conclusive demonstration of the globular figure of the earth independent of of its diurnal and annual revolution but if the diurnal rotation of the earth be admitted then we shall have almost every side ot the earth successively turned towards the sun and eclipses happening within a comparatively short period of time under all these conditions dit ions by such observations as these the earth is proved to be of a globular form by the most incontrovertible evidence when wo we come to speak of the diurnal rotation of the earth upon its axis we shall again refer to its figure and show that there is a slight deviation rivia hivia tion from the globular form arising from causes connected with that motion but for all practical purposes wherein great nicety or precision is not required the errors which arise by assuming the earth to be a perfect sphere will be inappreciable objections have been raised to the globular form of the earth on the ground that the great inequalities existing on its surface under the name of mountains and valleys are inconsistent with such a form lorm but the highest mountains of our globe when compared with the earth itself would be only about one ono sixteen hundredth part of its diameter the roughness on the surface of an orange is far greater when compared with the ma magnitude of the orange than is the roughness of the surface of the globe when compared with its magnitude indeed if our globe were reduced to the size of an orange the mountains delineated upon its surface if reduced in the same por portion would require a microscope of considerable power to clearly discover them having determined that the earth is a globe we shall next inquire how its ma magnitude may be determined if any mean means s can be des devised by which we can measure the circumference odthe of the earth its diameter together with the tho number of square mites miles upon its surface and also its solid contents can be easily calculated now to measure the whole circumference of the earth with a chain or line or any other accurate measure would be altogether impracticable en on account of mountains oceans swamps and other opposing obstacles but if we can accurately measure a portion of this circumference for instance one degree ot of laiti latitude tude and find how many miles it contains all that would be saly would be to multiply the number of miles in one degree by which is the number of degrees in the whole circumference of the earth ea rth nth and the product would be the number of miles around the earth now a degree may bo measured as follows let the latitude of this tabernacle be accurately taken by some astronomical instrument of great perfection then measure due south until you reach the southern extremity of the valley being careful to select a measuring rod whose length has been wen determined with the greatest possible accuracy when this measuring rod is used it must each time be carefully adjusted to a perfect level and ture tire noted for the length of any metallic b bar ar varies vanies with its temperature when the measurement is finished at the he southern extremity erect your astronomical instrument and by a series of observations of the heavenly bodies determine the latitude of this second station which we will say sar is one half of a degree south of the first station and the distance measured we will also say bay is miles this doubled 69 miles or the length of one de do gre greeting ethis multiplied by would give miles for the circumference of the earth this divided by would give miles for its diameter As the average length of a degree is not quite ogi 69 miles these numbers are rather too large to those unaccustomed to traveling ft is difficult to |