Show 1 MIEL astronomical LECTURES BY BT PROF ORSON THIRD IRD lit Is this lecture ye ve shall offer another conclusive evidence of tile the rotation of the earth derived from froin 1 the phenomena of the trade winds it is well known that in the tropical regions the general genera tendency of the currents current of our atmosphere is in I 1 the northern hemisphere from tile the northeast north east anil and in the southern southe im from tile the southeast south east the causes of these two great gedat currents are the high lempera temperature pera ture oft life torrid toi rid zone compared with that of the temperate aud and frigid zones find and second the tent tendency lency of the ahe air to expand by an increase of temperature by which it becomes specifically lighter and add arises while the vacancy thus occasioned is supplied aupp bied by a current front the colder regions these cu currents arents produced by the unequal temperature of the atmosphere surrounding the earth are modified in their direction by the rotation of the earth it is a fact established by observation that the sun is constantly vertical over some portions of the torrid zone embracing an extent of nearly mearly 47 deg in breadth surrounding the whole earth this zone which is over miles in breadth is maintained maintain ad at a much higher temperature than the other portions of the earth consequently theair the air in that zane z ne being raised to a higher temperature is rendered lighter and rises to higher regions the colder air from the north and south nearer the poles rushes in towards tire the torrid regions to supply the vacancy and restore the equilibrium this in its tui n becomes 1 heated and rises while its pla place e is ii immediately supplied applied up plied by air from the colder zones and thus if the earth had find no rotation there would be two rents of air one coining directly from the northern polar regions and the other coming coining directly from the southern while in the torrid zone there would bea be constant ascending current this ascending current would be deflected in the higher regions of 11 the atmosphere towards the north arid and towards to the south to supply the vacancies near the poles occasioned by the rushing of the lower currents towards the equator thus there would be a constant north wind near the surface of tile the earth in the northern hemisphere while in the upper regions a constant south wind would prevail to restore the equilibrium in the north temperate arid and frigid zones and rd in the southern hemisphere there would be a constant south buth wind near the surface of the earth and a constant north wind in the higher regions of the atmosphere mo sphere to restore the equilibrium in the south temperate and frigid zones these phenomena would take place were the earth at rest while the sun un had a diurnal rotation around it let us ua next inquire how these northern and southern currents would be modified in their directions by the diurnal rotation of the earth the atmosphere mo sphere revolves with the earth from west tyeast to east i consequently the equatorial atmosphere lias has a velocity of more than 1000 miles per hour while in I 1 F those regions nearer the poles the atmosphere has haa a velocity much slower and at the poles its velocity is reduced to nothing suppose that by some powerful impulse the polar atmosphere should be suddenly transferred to th the e equator it is evident that the air thus transferred having little or no rotation would be unable to keep up with the velocity of the equatorial surface which would run away from it to the eastward with the rapid velocity of 17 miles per minute this would produce one of the most violent violen t hurricanes from the east the velocity of the wind would be more that of a cannon ball nothing pothina would be able to withstand its fury the mountains and solid rocks chein selves would be torn from their foundations and carried with inconceivable velocity to the westward 1 the fury of the tempest would gradually abate as the air b by y friction gradually acquired the velocity of the earths rotation lot let us next suppose that the polar atmosphere 1 instead of being suddenly transferred to the equator I 1 be gradually transferred there to supply the vacancies occasioned by the ascending currents it la is evident chatin thai in every point of its progress towards its new situation its velocity would be insufficient to keep up with the new surface over which lyt I 1 is constantly passing hence it would constantly Tl feg 9 behind belli nd new surface or in other oilier words s tins i 09 surface would have a greater greata r velocity of rotation to wards the east than tha current of air has baa which S has come from the polar regions hence this current would appear to come from tile the east with a velocity equal to the differences of the velocities of their rotations tat ions this cause alone would produce an east wind which combined with the velocity towards howardi i the equator would in the northern hemisphere change it to a northeast north east wind and in in the southern i I 1 hemisphere hemi mollere sol lere the same two causes would give a bouth bout h east wind that these are the directions of i the trade winds near the n and southern tropics is ia a fact abundantly confirmed by bj observation L I 1 were it not for the rotation of the earth these i trade ahida as we have before stated would be I 1 northerly and southerly winds but by the t I 1 i unequal velocities of rotation b between the surfaces of odthe the earth and these carvents car rents passing over them I 1 1 they tire are deflected into permanent northeasterly north easterly and southeasterly south easterly winds I 1 11 we have already stated that a rapid transfer of air air from f rout the poles to the equator equa tr would woul pr aduce a 1 I 1 I 1 hurricane of the most destructive character but in general the transfer is is gradual and the friction of the earth is constantly accelerating its veli boniv I 1 the difference between the lengths of the ai diurnal circles 1 sn increase crease very slowly in the torrid zone aone and for several degrees each side aide of the equator the 0 change bantre is scarcely perceptible the friction of odthe the parth earth therefore he has more time to reduce the I 1 air to a state of relative rest and thus to destroy the easterly character of the currents and also the northern and southern currents when they have arrived in the neighborhood I 1 of the equator op oppose P e and neutralize each other and thus destroy their t hos air tendency to proceed in any particular direction in preference to another I 1 in this way there will be formed 4 an air equatorial belt where the air will be comparatively calm and on each side of this there will be formed two tropical belts encircling the whole earth where the trade winds will prevail these trade winds constantly blowing in a direction bontra contrary i ry to the diurnal rotation of the earth would by their friction upon its surface retard that rotation and finally destroy it altogether were it not for the compensating effect of the upper currents of the atmosphere these upper currents in the equatorial regions have it a velocity of over 1000 miles per haur haurand mild as they proceed towards the polar regions to supply the th vacancies produced by the ander currents their velocity velo cily of rotation is much greater than tile the velocity of the earths surface nearer the poles the consequences are that these currents as they are sucked sacked down arid and eone in contact with the earth s surface have a tendency to outrun it producing a strong westerly wind which combined with its original ori original rinal direction towards the poles forms forine in the northern temperate and frigid zones a southwesterly south westerly wind and in the t he southern bouthern ou thern temperate and frigid zones a northwester north wester weste r ly wind it will be observed that the courses of these currents are in direct opposition to the trades therefore they have a tendency te to accelerate the earths rotation ori as much as the trade winds have to retard it I 1 a this way the diurnal rotation is still at ill m at a uniform rate the direction dir action of these general currents is in different parts of the earths surface more or less I 1 influenced by b y local causes by which their permanent character is in a measure weakened and in some places entirely destroyed but where these causes do not interfere the permanency of their directions is abundantly est abolished ablis hed by observation and therefore these phenomena are cc conclusive evidence odthe diurnal rotation oj of the eartle in a direction irom from west to east cast having ascertained the true figure dimensions and rotation of the earth we shall next point out the methods by which its whole weight is determined if the earth opre wt re formed of one kind af f material as for instance lead or water or any one species of tocks rocks it would be an easy matter to determine its weight by knowin knowing g its dimensions for by know tag ing the number of pounds contained in one solid such material and multiplying the same into VAs ti number of solid feet in the wh while ie earth the product would be equal to t the number of pounds which use the whole onith would weigh the earth I 1 I 1 I 1 bonalin however consi ts 0 of a great variety of substances of different weight and if we knew the exact proportional bulk of each of these substances sub stane which enters into the earth s composition it would still be an easy matter to determine the weight of the I 1 whole by determining separately the weight of each proportional part but it is impossible for us to ascertain of what ingredients the interior strata of our earth cirth is ia com compoe used pd I 1 a and n d still more inert so to learn I 1 the proportional proportion a I 1 vo volumes 1 ut n 0 or r bulks of those 1 I Vs therefore all hopes of determining this problem from froin such data is forever banished the problem to ascertain the weight of the earth was not solved until toward the sose close of the lat century when two eminent arid and celebrated philosophers achieved its solution alution ol ution by different diff differs ernt rit methods arid and the results obtained were such ai a to give us an all assurance as urance of their accuracy we shall first give dr Maske lynea method in the year 1773 this great man being then astronomer tro nomer royal roya in england in connection with several other scientific gentlemen were engaged in making a series of exper experiments i upon the attractions of mountains A great number of observations were made by theira on th the e in mountain hallien in scotland A plum bline being suspended near the bue base of tile the mountain upon one side it was found to deviate from cwm the perpendicular towards the mountain tile same experiment was tried on the opposite side of the mountain and the plumb line was now found to t deviate in the contrary direction r being still drawn towards the mountain the amount of the deviation from tile the perpendicular was after about four months careful observations determined to be about 5 34 3 4 seconds of a degree in this way the proportion of the mass of the mountain to that of the whole earth may be determined prof playfair PI 1 fair some thirty years year atter afterwards by numerous measurements and observations determined tile the solid contents of the mountain and alai ala the nature of the strata strat a of which it is is composed from these data in connection with those obtained from froin tile the plum bline experiments the density of the rocks composing that mountain was found to be a trifle more than 1 12 2 the density of th the whole earth and about 2 12 1 2 times the th density of water consequently the density of the earth must be over five tunes thal thai of water that is is tile the earth as a whole will weigh about 5 times more than a globe of water of the same dimensions di mensina 1 in in other words about 5 globes of water of the same size as the earth would just counterpoise the earth I 1 the meth method 0 d adopted by mr cavendish for the solution of this problem was altogether of a different nature being founded upon a principle of dynamics or upon the laws which govern bodies in in motion it is is well known that tire the vibrations of a common pendulum attached to the machinery of a clock f for or measuring trine time are produced by the force of gravity driy that force winch which causes all bodies to fiall fall towards the centre of the earth this force acting upon the matter of which the ball or disc of the pendulum is is composed causes it to vibrate in in a certain time if the force were wele greater the vibrations of the same pendulum would be more rapid if it were ivere less the vibrations would be slower this is is exemplified as we vie ba have ve already observed in in the difference of the number of vibrations that take place in a given time in in different latitudes tire the ra rate te of vibration of a pendulum therefore is is the true meas measure ure of the forve force by which it is is moved from these facts it is is evident that two pendulums which will vibrate in in equal times under the in influence of the same force will if acted upon by forces of different intensities vary the rate of their vibrations suppose then that ese two pendulums were made to vibrate at al the surfaces of two different globes globe which w aich contained unequal quantities of the force called gravity the rate of vibration would determine the proportional quantity of force existing in in the two globes and it the force or weight of one be known the force or weight of the other can call be easily calculated from the proportional quantities it wis was upon this principle that IV mr r cavendish made iris ins experiments to determine the weight of the earth lie he procured a metallic globe of known weight and suspended near its surface a fine needle in in a horizontal position the point of its suspension was w as the centre of its gravity therefore the extremities of the in ciet dk n uld h hn vc no t j t tu dip t 1 41 the earth by the force of gravity in this position the needle would vibrate in a horizontal position with w ith out being affected in in the least by the earths grai bravi ty the horizontal vibration depended upon the torsion or twisting tw biting of the filament by which it was suspended placing this pendulum near the surface of tile the metallic globe in in such a position that tile point of the needle was v as directed towards its centre it was made to vibrate in lit a horizontal plane under tile influence fluence hi oatlie of the same mechanical conditions condi firis as the vibrations of a common clock pendulum which vibrates in in a pi plane me passing through the centre of the earth the nun number ber of vibrations made in in a given time by each of these pendulums was counted then we bave the necessary data for solving tine this great problem for the square of tire the number of oscillations of the horizontal pendulum affected by the metallic globe is is to the square of the num her ber of oscillations of tile the vertical or clock pendulum affected by tile the earth as the weight of the metallic globe is to the weight or of the whole earth by these experiments and calculations cavend ish found tile the weight of tile the earth to be about the same as determined by b y dr maskelyne and thus the same conclusions were obtained irom froin methods entirely dissimilar it ins has thus been satisfactorily established that th it the weight of the earth is is a little more thin than five times greater than the weight of its own bulk of water from extensive observations of the nature of the earths surface in in various various parts of the globe it is is very certain that tha t it cannot have |