Astronomers From England

"Three years after this discovery, by which Mr. Bradley acquired very great reputation, he was appointed Lecturer in Astronomy and Physic, at the Museum at Oxford. He pursued his studies with equal application and delight; and in the course of his observations... he discovered that the inclination of the Earth's axis, upon the plane of the , was not always the same, but that it varied backwards and forwards some seconds, and that the period of these variations was nine years. This period seemed altogether unaccountable, as it could not be supposed to have any thing in common with the revolution of the Earth, which is performed in one year. Mr. Bradley, however, discovered the cause of this phenomenon in the Newtonian system of attraction. The first principle of that system is known to be, that all bodies mutually attract each other in the direct ratio of their masses, and in the inverse ratio of the squares of their distances. From this mutual attraction, combined with motion in a right line, Newton deduces the figure of the orbits of the planets, and particularly that of the Earth. If this orbit was a circle, and if the terrestrial globe was a perfect sphere, the attraction of the Sun would have no other effect than to keep it in its orbit, and would cause no irregularity in the position of its axis; but neither is the Earth's orbit a circle, nor its body a sphere; for the Earth is sensibly protuberant towards the equator, and its orbit is an ellipsis, which has the Sun in its focus. When the position of the Earth is such, that the plane of its equator passes thro' the centre of the Sun, the attractive power of the Sun acts only so as to draw the Earth towards it, still parallel to itself, and without changing the position of its axis, and this happens at the equinoxes. In proportion as the Earth recedes from those points, the Sun also goes out of the plane of the equator, and approaches that of one or other of the tropics; the semidiameter of the Earth, which is then exposed to the Sun, being no longer equal, the equator is more powerfully attracted than the rest of the globe, which causes some alteration in its position, and its inclination upon the plane of the ecliptic; and as that part of the orbit, which is comprized between the autumnal and vernal equinox, is less than that which is comprized between the vernal and the autumnal, it follows, that the irregularity caused by the Sun, during his passage through the northern signs, is not entirely compensated by that which he causes during his passage through the southern signs; and that the parallelism of the terrestrial axis, and its inclination with the ecliptic, will be a little changed. But though the irregularity is now accounted for, we are still at a loss for the cause of its happening in a period of nine years. This difficulty, however, will immediately disappear."

"Bradley, upon his being elected into this professorship, gave up both his livings, and with great joy quitted a situation in which his duty was directly opposite to his inclination. From this time he applied himself wholly to the study of his favourite science, and in the year 1727, he published his theory of the aberration of the fixed stars, which is allowed to be one of the most useful and ingenious discoveries of modern astronomy."

"He was remarkable for a placid and gentle modesty, very uncommon in persons of an active temper, and robust constitution. It was still more remarkable, that with this untroubled equanimity of temper, he was compassionate and liberal in the highest degree. Although he was a good speaker, and possessed the rare, but happy art of expressing his ideas, with the utmost precision and perspicuity, yet no man was a greater lover of silence, for he never spoke, but when he thought it absolutely necessary. He did indeed, think it necessary to speak when he had a fair opportunity to communicate any useful knowledge in his own way, and he encouraged those that attended his lectures, to ask him questions, by the exactness with which he answered, and the care he took to adapt himself to every capacity."

"He was nephew to Mr. Pound, a gentleman who is well known in the learned world by many excellent observations, and who would have enriched it with more, if the journals of his voyages had not been burnt at Pulo Condor, when the place was set on fire, and the English who were settled there cruelly massacred... With this gentleman, Mr. Bradley passed all the time that he could spare from the duties of his function; and perhaps he sometimes trespassed upon them; he was then sufficiently acquainted with the mathematics to improve by Mr. Pound's conversation, yet it does not appear that in this study, he had any preceptor but his genius, or any assistant but his labour."

"He continued... to fulfill the duties [of holy orders]... though at this time he had made such observations as laid the foundation those discoveries which afterwards distinguished him as one of the greatest astronomers of his age. Though these observations were made as it were by stealth, they gained him first the notice, and then the friendship of lord chancellor Macclessield, Mr. Newton, afterwards Sir Issac, and Mr. Halley, and many other members of the royal society, into which he was soon elected a member."

"Dr. James Bradley was the third son of William and Jane Bradley, and was born at Sherborne in Dorsetshire in the year 1692. He was fitted for the university at North Leach [at] a boarding school... and from [there] he was sent to Oxford."

"About the fame time the chair of at Oxford became vacant, by the death of the celebrated Dr. Keil; and Mr. Bradley was elected to succeed him on the 31st of October 1721, being then just nine and twenty years old; and his colleague was Mr. Halley, who was professor of Geometry on the same foundation."

"His friends intended him for the church, and his studies were regulated with that view; and as soon as he was of sufficient age to receive holy orders, the bishop of Hereford, who had conceived a great esteem for him, gave him the living of Bridstow, and soon after he was inducted to that of Welfrie in Pembrokeshire. But, notwithstanding these advantages, from which he might promise himself still farther advancement in the church, he at length resigned his livings that he might be wholly at liberty to pursue his favourite study, the mathematics and particularly astronomy."

"For common purposes we may without sensible error suppose the earth's motion equable and neglect the corrections, and then the rule for the parallax of will be this: Sine lat. : rad. : : cotang. A : cotang. C, or rad : sine lat. : : tang. A : tang. C; then long. star \mp C = long. of λ. Cosine C : cosine A : : semi transverse axis : z. And cosine decl. cosine (ʘ - λ) :: z : x = parallax of right ascension."

"I would by no means attempt to infer from hence, that the longitude found by observations of this sort may in all cases be depended upon within one degree; but I beg leave to observe, that whatever extraordinary circumstances may have concurred to produce so near an agreement in this particular case, the event is such as may give reason to hope, however great the difficulties of finding the longitude by this method seem to be, that they are not insuperable, or such as ought to deter those whom it most nearly concerns from attempting to remove them."

"The invention of the telescope, the application of the pendulum to clocks, the invention of the micrometer, the combination of the telescope with the divided arc of a circle, invention of the transit circle by Roemer, with many improvements in minor apparatus, distinctly stamp the [17th] century as a remarkable period of preparation for achievements of the next century. From the standpoint of the modern mechanician the instruments at the Greenwich Observatory in Bradley's time were very imperfect in design and construction, and yet on the observations obtained by his skill and perseverance depends the whole structure of modern fundamental astronomy. The use the quadrant reached its highest excellence under Bradley's management. ... Bradley's observations furnish the data for Bessel's "Fundamenta Astronomiae," and many astronomers have since attempted by reductions to obtain improved positions for Bradley's stars. The value of these observations in the development of modern astronomy can hardly be exaggerated. Their importance in the determination of stellar s increases with the lapse of time, and yet the accuracy of the original observations was far inferior to that obtained in ordinary routine work with modern methods and improved instruments."

"When the year was completed, I began to examine and compare my observations, and having pretty well satisfied myself as to the general laws of the phenomena, I then endeavored to find out the cause of them. I was already convinced that the apparent motion of the stars was not owing to the of the earth's axis. The next thing that offered itself was an alteration in the direction of the plumb-line with which the instrument was constantly rectified; but this upon trial proved insufficient. Then I considered what refraction might do, but here also nothing satisfactory occurred. At length I conjectured that all the phenomena hitherto mentioned, proceeded from the progressive motion of light and the earth's annual motion in its orbit. For I perceived that, if light was propagated in time, the apparent place of a fixed object would not be the same when the eye is at rest, as when it is moving in any other direction than that of the line passing through the eye and the object; and that, when the eye is moving in different directions, the apparent place of the object would be different."

"My Instrument being fixed, I immediately began to observe such Stars as I judged most proper to give me light into the Cause of the Motion... There was Variety enough of small ones; and not less than twelve, that I could observe through all the Seasons of the Year; they being bright enough to be seen in the Day-time, when nearest the Sun. I had not been long observing, before I perceived, that the Notion we had before entertained of the Stars being farthest North and South, when the Sun was about the Equinoxes, was only true of those that were near the solstitial Colure: And after I had continued my Observations a few Months, I discovered what I then apprehended to be a general Law, observed by all the Stars, viz. That each of them became stationary, or was farthest North or South, when they passed over my Zenith at six of the Clock, either in the Morning or Evening. I perceived likewise, that whatever Situation the Stars were in with respect to the cardinal Points of the Ecliptick, the apparent Motion of every one tended the same Way, when they passed my Instrument about the same Hour of the Day or Night; for they all moved Southward, while they passed in the Day, and Northward in the Night; so that each was farthest North, when it came about Six of the Clock in the Evening, and farthest South when it came about Six in the Morning."

"Seventy years have nearly elapsed since the death of Bradley and the generation of those who knew him has passed away some little however might be expected to remain in traditionary remembrance The rapid course of time would soon have swept away that little and have impaired some of the means which are still in our power for understanding what may exist in written documents It seemed desirable therefore to try what might yet be collected and though it proved to be far short of what could be wished I indulge the hope of its being authentic and accurate."

"I give all my printed books to Samuel Peach, son of Samuel Peach, in my Will named, and desire that this may be a codicil to my last Will and Testament, and taken as part thereof, as witness my hand, this third day of December. in the year of our Lord 1761."

"If we suppose the distance of the fixed stars from the sun to be so great that the diameter of the earth's orbit viewed from them would not subtend a sensible angle, or which amounts to the same, that their annual is quite insensible; it will then follow that a line drawn from the earth in any part of its orbit to a fixed star, will always, as to sense, make the same angle with the plane of the ecliptic, and the place of the star, as seen from the earth, would be the same as seen from the sun placed in the focus of the ellipsis described by the earth in its annual revolution, which place may therefore be called its true or real place. But if we further suppose that the velocity of the earth in its orbit bears any sensible proportion to the velocity with which light is propagated, it will thence follow that the fixed stars (though removed too far off to be subject to a parallax on account of distance) will nevertheless be liable to an aberration, or a kind of parallax, on account of the relative velocity between light and the earth in its annual motion. For if we conceive, as before, the true place of any star to be that in which it would appear viewed from the sun, the visible place to a spectator moving along with the earth, will be always different from its true, the star perpetually appearing out of its true place more or less, according as the velocity of the earth in its orbit is greater or less; so that when the earth is in its perihelion, the star will appear farthest distant from its true place, and nearest to it when the earth is in its aphelion; and the apparent distance in the former case will be to that in the latter in the reciprocal proportion of the distances of the earth in its perihelion and its aphelion. When the earth is in any other part of its orbit, its velocity being always in the reciprocal proportion of the perpendicular let fall from the sun to the tangent of the ellipse at that point where the earth is, or in the direct proportion of the perpendicular let fall upon the same tangent from the other focus, it thence follows that the apparent distance of a star from its true place, will be always as the perpendicular let fall from the upper focus upon the tangent of the ellipse. And hence it will be found likewise, that (supposing a plane passing through the star parallel to the earth's orbit) the locus or visible place of the star on that plane will always be in the circumference of a circle, its true place being in that diameter of it which is parallel to the shorter axis of the earth's orbit, in a point that divides that diameter into two parts, bearing the same proportion to each other, as the greatest and least distances of the earth from the sun."

"When Bradley's observations of γ Draconis were corrected for abberation, they showed, according to himself, that the parallax of that star could not be as much as 1".0 or that the star was more than 200,000 times as distant from the earth as the sun."

"Sir, Having long deferred to make any report relating to the observations that were taken at sea by captain Campbell, in the year 1757, which you transmitted to me by order of the lords of the admiralty, I think it necessary to acquaint you, that, upon examining those observations, I perceived that they were not in all respects accompanied with such circumstances as are requisite for forming a right judgment of the accuracy and certainty with which observations proper for finding the longitude at sea by the moon can in fact be taken; for which reason I delayed giving my opinion upon this point till I could have an opportunity of comparing a greater variety of observations, made at different times, and with different instruments: such an opportunity having lately been given me by captain Campbell, who has favoured me with a copy of several observations that were made by him in 1758 and 1759, I now beg leave to lay before their lordships the result of the comparisons which I have made."

"James Bradley, the third Astronomer Royal of Greenwich, was born at Sherbourn, in Gloucestershire, in the year 1692. In 1711 he entered Baliol College, Oxford, where he completed his education. Having qualified himself for the church, he was presented to a living in the year 1719. His predilection for astronomical pursuits, which evinced itself at an early age, was fostered by his uncle, the Rev. . with whom he resided for several years at Wanstead, in Essex. In 1721 he was appointed to the Savilian chair of astronomy in the University of Oxford, which had then become vacant by the death of Keill. His nomination by the Government, as successor to Halley in the Observatory of Greenwich, is dated February 2, 1742. His reputation as an astronomer was already well established in Europe by observations of a miscellaneous nature, and more especially by his immortal discovery of the Aberration of Light, and at the time of his appointment he was actually engaged in those researches which resulted in his discovery of the Nutation of the Earth's axis."

"Bradley's first object after his removal to Greenwich was to repair the instruments, and carefully to adjust their positions. Halley had confined himself to the use of the mural quadrant soon after its erection in 1725. Bradley, however, resolved to employ both the quadrant and the transit instrument in his observations. The former of these instruments was repaired by Graham, and the latter by Sisson, several important improvements being at the same time effected in their construction. Bradley's first observation with the quadrant was made on the 15th of June, 1742. His earliest transit observation is dated the 20th of July in the same year."

"Bradley being new in possession of instruments of unequalled perfection, proceeded to execute a series of preliminary observations for the purpose of ascertaining with greater accuracy the latitude of his observatory, the place of the equinox, the quantity and laws of refraction, and other fundamental points of astronomy. In pursuance of this design the brass quadrant was... employed in making observations of s. ...From them Bradley deduced the latitude of the observatory to be 51° 28′ 38½″. He also succeeded by means of them in constructing the elegant rule, so long used by astronomers, for finding the quantity of corresponding to any assigned zenith distance, and any observed readings of the barometer and thermometer. He determined the absolute right ascensions of a few of the principal stars, by means of observations made near the equinoxes, according to the method of Flamsteed."

"As soon as Bradley had established these fundamental points he removed the brass quadrant from the western face of the meridian wall, and permanently attached it to the eastern face, where it was afterwards employed in observing the stars that passed the meridian to the south of the zenith. At the same time the iron quadrant was removed from the eastern face of the wall, and, after being re-divided by Bird, was attached to the western face, for the purpose of making observations with the telescope turned towards the north. Bradley now commenced the series of admirable observations which have formed the groundwork of so much valuable research to future enquirers, and which would have assured to him an immortal reputation, even independently of those great discoveries with which his name is inseparably associated. The sun, moon, and principal stars, and the planets when situate in favourable positions, were regularly observed with the transit instrument and the mural quadrants. Moreover, a multitude of small stars, chiefly those of Flamsteed's catalogue were included in the plan of observation. From the year 1750 may be dated the commencement of a series of observations which in point of accuracy may bear a comparison with those of modern times. Henceforward the records of Greenwich Observatory embody a collection of materials, which have almost exclusively formed the groundwork of every investigation undertaken in modern times, for the purpose of improving the solar, lunar, or planetary tables."

"The registers of Bradley's observations occupied thirteen folio volumes, and at his death were taken possession of by his executors. In 1767 the Government, under the impression of their being public property, commenced a law-suit with a view to their recovery, which, however, they abandoned in 1776. As soon as it was ascertained that the Government had relinquished their claim, the manuscripts were transmitted to Lord North, who was then Chancellor of the University of Oxford, to be presented by him to the University. They were finally printed, at the expense of the University, in two folio volumes. The first volume was published in 1798, under the superintendence of Dr. Hornsby. The second volume was prepared for the press by Dr. Robertson, and appeared in 1805. These two volumes contain the observations made by Bradley, from 1750 to 1762. The original manuscripts, as well as the registers of the observations made by Bradley, at Greenwich, previous to 1750, are deposited in the , Oxford."

"The vast mass of observations made by Bradley... two volumes... continued inapplicable to any useful purpose, in consequence of their not being reduced, until... Bessel undertook to execute this task... The results of his labours were published in 1818, at Königsberg, in one folio volume, entitled Fundamenta Astronomiæ pro anno 1755, deducta ea Observationibus viri incomparabilis James Bradley, in specula Astronomica Grenovicensi per annos 1750 1762 institutis. In this work Bessel has determined, by a series of elaborate investigations, the quantity and laws of refraction, the maximum value of aberration, and other fundamental points of astronomy, as deducible from Bradley s observations."

"To obtain a greater degree of permanence the time symbols of oral speech had to be converted into the space symbols of written speech. ...The crucial stage in the evolution of writing occurred when ideographs became phonograms..."

"Language itself inevitably introduced an element of permanence into the world. For, although speech itself is transitory, the conventionalized sound symbols of language transcended time."

"Our idea of the universe as a whole remains a product of the imagination."

"It must have required enormous effort for man to overcome his natural tendency to live like the animals in a continual present."

"The development of rational thought actually seems to have impeded man's appreciation for the significance of time. ...Belief that the ultimate reality is timeless is deeply rooted in human thinking, and the origin of rational investigation of the world was the search for permanent factors that lie behind the ever-changing pattern of events."

"The history of natural philosophy is characterized by the interplay of two rival philosophies of time — one aiming at its "elimination" and the other based on the belief that it is fundamental and irreducible."

"The basic objection to attempts to deduce the unidirectional nature of time from concepts such as entropy is that they are attempts to reduce a more fundamental concept to a less fundamental one."

"It became clear that our Galaxy is only one system among many, and that the universe is far vaster than the particular stellar system to which the Sun and planets belong. Since then developments have been more rapid than at any time since the days of Copernicus, Digges and Bruno when the geocentric hypothesis of the cosmos received its death-blow."

"Man must have been conscious of memories and purposes long before he made any explicit distinction between past, present, and future."

"The point at issue between the two theories [A and B theory] is whether 'time' really is, in some deep ontological sense, differentiated into past, present and future. ...Reichenbach and Whitrow propose that there is indeed such a type of event and this is the 'becoming', or 'coming into being' of factual states-of-affairs in the physical world. ...Whitrow expressed ..."The past is the determined, the present is the moment of 'becoming' when events become determined, and the future is as-yet undetermined. Although neither Reichenbach nor Whitrow developed their thesis at any length, the general purport of what they meant is clear: there is a basic chance element in nature, at least at the micro-level, and the moment of 'becoming', which they identify with 'the present', is marked by a tranisition from what is merely possible to what is factual. However... this important attempt to provide a physical basis for the A-theory is by no means immune from criticism."

"The famous palaeolithic paintings found in caves such as that at Lascaux in the Dordogne have been interpreted as evidence that, at least implicitly people were operating 20,000 or more years ago with teleological intent in terms of past, present, and future. It may well be that those responsible for the so-called 'Dancing Sorcerer' ...may have felt that the actual performance of the dance was insufficient, since they were concerned with the magical efficacy of the dance after it ended."

"Most of the illustrations in this book were scanned... from the volumes in which they originally appeared. One of these deserves special mention. It is... from the library of the late Gerald James Whitrow... I was honoured to receive this small book as a gift in 2001 from Professor Whitrow's widow, Magda... I wished to include a copy of this historic image in my own book both as a tribute to Pofessor Whitrow's memory and to express my sincere gratitude to all responsible for the gift."

"Whitrow... proposed an anthropic resolution of the venerable philosophical question Why physical space has three dimensions? (arguing that with a space of different dimensionality there would be no living being to pose the question) and, similarly to [Grigory Moiseevich] Idlis, alluded around 1955 to an anthropic explanation of the size of the observable universe. Anyway, he never published these last ideas, which were developed years later by Wheeler. The only reference to Whitrow’s argument that appeared in print during the 1950s seems to be that due to the philosopher of religion Eric Lionel Mascall, who attributed to the English’s mathematician thatit may be necessary for the universe to have the enormous size and complexity which modern astronomy has revealed, in order for the earth to be a possible habitation for living beings."

"While at Oxford, he was much influenced by cosmologist, E. A. Milne. ...Whitrow is... remembered for his very loud voice which could be heard 'from miles away.'"

"Not until the pioneer work of Rutherford and his colleagues was the possibility of nuclear reactions and transformations as sources of stellar energy envisaged."

"The solution... was found only after the rise of nuclear physics, and, strange to relate, was not known to Eddington when he developed his celebrated theory of stellar structure between 1916 and 1924. Indeed, it is one of the most intriguing facts in the history of science that the two most influential theories concerning the stars—Newton's theory of gravitation and Eddington's theory of stellar construction—were each developed so successfully although Newton was ignorant of the origin of gravitation and Eddington of the origin of stellar energy."

"Newton's laws of motion and gravitation achieved their original success when applied to the solar system. The first definite evidence that they were applicable on a larger scale came from the study of binary stars towards the eighteenth century. In recent times the limitations of Newton's theory have become apparent. Even on the scale of the solar system, it has been challenged by Einstein's."

"By the time of Comte, scientists unanimously rejected the idea that there was any essential difference between celestial and terrestrial matter, but they still had no empirical evidence to support their view any more than had Aristotle to support his, and to the positivist philosopher it seemed that none could ever be obtained. ...The possibility of a solution to this problem appeared shortly after Comte's pronouncement with the rise of the science of astronomical spectroscopy..."

"The models of Einstein and de Sitter are static solutions of Einstein's modified gravitational equations for a world-wide homogeneous system. They both involve a positive cosmological constant λ, determining the curvature of space. If this constant is zero, we obtain a third model in classical infinite Euclidean space. This model is empty, the space-time being that of Special Relativity. It has been shown that these are the only possible static world models based on Einstein's theory. In 1922, Friedmann... broke new ground by investigating non-static solutions to Einstein's field equations, in which the radius of curvature of space varies with time. This Possibility had already been envisaged, in a general sense, by Clifford in the eighties."

"From a careful determination of the amount of solar heat that which would fall per minute on an area of one square centimetre placed perpendicular to the radiation as it falls on Earth's surface and from a knowledge of the Earth's distance, we deduce that each square centimetre of the solar surface radiates on the average of about the rate of a nine horse-power engine."

"As the degree of observational accuracy at which general relativity becomes significantly different from Newtonian theory is far from being achieved in this field, and as stellar velocities are small compared with light, there is no sign yet that any non-Newtonian theory is required."

"The philosophical consequences of the General Theory of Relativity are perhaps more striking than the experimental tests. As Bishop Barnes has reminded us, "The astonishing thing about Einstein's equations is that they appear to have come out of nothing." We have assumed that the laws of nature must be capable of expression in a form which is invariant for all possible transformations of the space-time co-ordinates and also that the geometry of space-time is Riemannian. From this exiguous basis, formulae of gravitation more accurate than those of Newton have been derived. As Barnes points out..."

"Although the Special Theory of Relativity does not account for electromagnetic phenomena, it explains many of their properties. General Relativity, however, tells us nothing about electromagnetism. In Einstein's space-time continuum gravitational forces are absorbed in the geometry, but the electromagnetic forces are quite unaffected. Various attempts have been made to generate the geometry of space-time so as to produce a unified field theory incorporating both gravitational and electromagnetic forces."

"Space-time is curved in the neighborhood of material masses, but it is not clear whether the presence of matter causes the curvature of space-time or whether this curvature is itself responsible for the existence of matter."

"In developing his theory of gravitation, Newton assigned to every material body another property which is called its gravitational mass. Gravitational mass determines the force exerted by the body on other bodies, and so its function appears to be quite distinct from that of inertial mass. Nevertheless, the two are found to be identical in magnitude. Newton made experiments to verify this remarkable equality by swinging a pendulum with a bob which could be made with different materials. The period of the swing depended on the ratio of the inertial and gravitational masses of the pendulum, but in all cases it was found to be the same... In 1890 Eötvös made a much more refined test with the aid of a... torsion balance. Repeated experiments showed that inertial mass and gravitational mass were equal to within one part in 100 million. Einstein suggested that this was because inertia and gravitation are identical."

"Minkowski made a remarkable discovery concerning the Lorentz formulae. He showed that, although each observer has his own private space and private time, a public concept which is the same for all observers can be formed by combining space and time as a kind of 'distance' by multiplying it by the velocity of light, c; in other words, with any time interval we can associate a definite spatial interval, namely the distance which light can travel in empty space in that period. If, according to a particular observer, the difference in time between any two events is T, this associated spatial interval is cT. Then, if R is the space-distance between these two events, Minkowski showed that the difference of the squares of cT and R has the same value for all observers in uniform relative motion. The square root of this quantity is called the space-time interval between two events. Hence, although time and three-dimensional space depend on the observer, this new concept of space-time is the same for all observers."