143 



RtiMER, OLAUS. 



14-1 



decorations for theatres. Having amassed a considerable fortune, he 

 commenced building a handsome mansion, but had not proceeded far 

 when he found bis means to be inadequate, and he pretended that the 

 Grand-Duke of Tuscany required his attendance at Florence, as an 

 excuse for not proceeding with the edifice. The mortification of this 

 disappointment is supposed to have hastened his death, which took 

 place at Antwerp in 1637, according to Houbraken, and according to 

 Weyermans in 1640. 



HOMER, OLAUS, a Danish astronomer, was born at Arhusen in 

 Jutland, in 1644, of parents who, though not in affluent circumstances, 

 were able to give their son the benefits of a scientific education by 

 sending him to the University of Copenhagen, where he applied him- 

 self diligently to the study of astronomy under Erasmus Bartholinus. 



He was brought into notice by Picard, who, in 1671, was sent from 

 France by Louis XIV. to make celestial observations in the north, and 

 to verify the position of Uraniburg, once the residence of Tycho 

 Brahe". The French astronomer conceived so great an esteem for the 

 talents of the young Dane, that he engaged him to visit Paris, and 

 when there procured for him the honour of being presented to the 

 king. In consequence of this introduction, Romer was appointed to 

 instruct the Dauphin in mathematics, a pension was settled on him, 

 and the next year the Royal Academy of Sciences made him a member 

 of their body. 



While in France, Romer was employed, together with Messrs. Cassini 

 and Picard, in performing geodetical operations for the survey of the 

 kingdom ; he also assisted at the Royal Observatory at Paris, and from 

 the observations which he had occasion to make on the immersions 

 and emersions of Jupiter's first satellite, he was led to the discovery 

 of certain inequalities in the times of the occurrence of these pheno- 

 mena, which had not before been noticed. It was then first remarked, 

 that between the times of the opposition of Jupiter to the sun and 

 the next following conjunction, the emersions of the satellite from the 

 shadow of the planet took place always later than the times indicated 

 by calculation, and that the difference between the observed and the 

 calculated times when the planet was near the points of opposition 

 and conjunction was about fourteen minutes. A contrary circumstance 

 was observed from the time of a conjunction of Jupiter with the sun 

 to the next following opposition ; for the immersions appeared to take 

 place more early than the calculated times, the difference of the times, 

 when near the points of conjunction and opposition, being also about 

 fourteen minutes. 



There appears however to be some uncertainty whether Romer or 

 Cassini (J. D.) is the astronomer to whom the honour of being the first 

 to perceive the inequality belongs ; and Montucla asserts not only 

 that the latter made the discovery, but that he gave an explanation of 

 its cause. He states that Cassini published in 1675 a paper in which 

 it is shown that the phenomena result from the difference between the 

 times during which the particles of light are passing from the satellite 

 to the earth (the planet being, when in opposition, nearer to the earth 

 than when in conjunction, by the whole diameter of the earth's orbit), 

 and in which it is inferred that the velocity of light must consequently 

 be such as to allow it to pass from the sun to the earth in about eight 

 or ten minutes. On the other hand, it is well known that Cassini at 

 first objected to the transmission of light through a part of space in 

 a certain time as a cause of the observed inequality, on the ground 

 that similar inequalities were not observed in the immersions or 

 emersions of the other satellites. Now it is more probable that the 

 French astronomer should have made objections to the hypothesis of 

 another man, than that he should have abandoned one which himself 

 had formed; and even if such abandonment had taken place, Romer 

 ought in justice to be considered as the real discoverer of this important 

 element in astronomical science, since it is admitted that he took up 

 the subject and gave a precise explanation of the circumstances. The 

 reason why the like retardation or acceleration of the times was not, 

 then, observed in the second and the remaining satellites is, that the 

 theory of the motions of those bodies was in that age so imperfect, that 

 the times of the phenomena could not be determined by computation 

 within the number of minutes to which the optical inequality amounts. 

 It is now well known that the latter takes place similarly in the 

 phenomena of all the satellites. 



Romer was as good a mechanician as an astronomer. It is to him 

 we owe the application of the epicycloidal curve in the formation of 

 the teeth of wheels, by which the movement is rendered uniform ; 

 and an account of the invention was sent to the Academy of Sciences 

 in 1675. De la Hire afterwards claimed the honour of having first 

 discovered the advantage of teeth so formed ; but Leibnitz, in a letter 

 to John Bernoulli, states that Romer had communicated the invention 

 to him twenty years before the date of De la Hire's publication. 

 Romer is said to have designed several machines for representing the 

 motions of the planets, and particularly one which exhibited the 

 revolutions of Jupiter's satellites : by this machine it is said that the 

 immersions and the emersions might be determined with great 

 precision. 



Having remained ten years in France, Romer returned to Copen- 

 hagen, where the king, Christian V., made him professor of astronomy. 

 He was at the same time employed in reforming the coin, in regulating 

 the weights and measures, and in making or repairing the public 

 roads. Having acquitted himself in the performance of these scientific 



commissions to the satisfaction of his sovereign, he was named chan- 

 cellor of the Danish exchequer, and assessor of the supreme tribunal 

 of justice. At length, under Frederic IV., he became burgomaster of 

 Copenhagen, in which city he died, September 19, 1702, having 

 suffered at intervals from the stone during the three last years of 

 his life. 



Peter Horrebow, one of his pupils and his successor in the chair of 

 astronomy, published (1735), under the title of 'Basis Astronomiae,' 

 the series of celestial observations made by Romer, with a description 

 of the observatory at Copenhagen, and an account of the manner in 

 which the instruments were used. 



In determining the apparent places of celestial bodies, it had, pre- 

 viously to the time of Romer, been the practice to observe their 

 altitudes and azimuths, and also their distances from one another or 

 from some body whose place was already found. The trouble of 

 computing the right ascensions and declinations from these elements 

 was considerable, and the Danish astronomer made an important 

 change in the practice of observing, by which this trouble was avoided. 

 He used what is called a transit telescope, with a clock, and also a 

 mural quadrant ; with these he observed directly the differences be- 

 tween the right-ascensions (in time) and between the decimations of 

 the sun and the planets or the fixed stars. It is right to remark 

 however that Picard had somewhat earlier fixed in the plane of the 

 meridian a telescope, by which he could, it is said, obtain altitudes 

 between 56 and 61. Now a space equal in extent to five 

 degrees cannot be seen at once in a telescope, and therefore it is 

 probable that this was moveable in altitude to that extent ; and if 

 Romer was at any time a witness to the performance of the instru- 

 ment, he may have taken from it the idea of making a telescope turn 

 on a horizontal axis through 360 degrees in the plane of the meridian. 

 It appears also that De la Hire contended with Romer for the 

 honour of having been the first to fix a quadrautal instrument in 

 that plane. 



ROMILLY, SIR SAMUEL, was born in London, on the 1st of 

 March 1757. His grandfather, a French Protestant, quitted Fi-ance in 

 consequence of the persecutions which succeeded the revocation of the 

 Edict of Nantes, and established himself in the business of a wax- 

 bleacher, in the neighbourhood of London. His youngest son, Peter, 

 the father of Sir Samuel Romilly, was brought up to the trade of a 

 jeweller, in which he became successful and eminent. Of the numerous 

 family of Peter Romilly, two sons and a daughter alone survived their 

 infancy, of whom Samuel was the youngest. The early education of 

 Samuel Romilly was extremely defective. He was sent with his 

 brother to a day-school, frequented by the children of the French 

 refugees in London, the master of which was ignorant and tyrannical, 

 and incompetent to instruct his pupils in anything beyond reading, 

 writing, and the rudiments of the French language. The elder brother 

 being intended for his father's trade, it was attempted to lead Samuel's 

 inclination to the business of a solicitor; but a disgust implanted in 

 his mind by a view of the discouraging apparatus of an attorney's 

 office in the city, caused the abandonment of this scheme. It was 

 then proposed to place him in the commercial house of the Fludyers, 

 who were near relations of his family, and one of whom, Sir Samuel 

 Fludyer, was his godfather. With a view to this employment he 

 received instruction in book-keeping and mercantile accounts, but the 

 death of both the partners in the house of Fludyer put an end to this 

 promising project, and his father, having failed in several other 

 schemes respecting him, eventually employed him in his own trade, 

 at first simply for the purpose of furnishing him with occupation, and 

 afterwards with the intention that the two brothers should succeed to 

 the business in partnership upon their father's retirement. 



During the intervals of leisure which were abundantly afforded him 

 for several years after he left school, at the age of fourteen, Samuel 

 Romilly applied himself assiduously to literary studies, which were 

 more suitable to his serious and somewhat melancholy disposition 

 than the usual exercises and amusements of youth. Ancient history, 

 English poetry, and works of criticism were at this period his favourite 

 objects of pursuit. When he was between fifteen and sixteen years of 

 age he determined to become acquainted with the Lathi language, and 

 by means of hard study, and with the assistance of a master, he 

 acquired so much proficiency as enabled him, in the course of three 

 or four years, to read through almost all the classical writers of Rome. 

 He also applied himself to Greek, but, discouraged by the difficulties 

 of self-instruction, he abandoned the attempt, and contented himself 

 with studying the Greek authors by means of Latin versions. In 

 addition to classical studies, he read travels, and acquired a competent 

 knowledge of geography, and some acquaintance with natural history ; 

 and he also attended private lectures on natural philosophy, and the 

 lectures on painting, architecture, and anatomy delivered at the Royal 

 Academy. 



It is not surprising that a devotion to such pursuits as these should 

 excite aspirations for an occupation more congenial to them than the 

 trade of a jeweller; and his indulgent father, whose pecuniary means 

 had been about this time increased by considerable legacies to his 

 family, and among them a bequest of 20001. to Samuel Romilly, readily 

 yielded to his son's wishes in this respect, and articled him for five 

 years to one of the sworn clerks in chaiicery. The object of serving a 

 clerkship of this kind was the purchase of a seat in the Six Clerks' 



