>S2 



NA TURE 



[January 22, 1903 



that the artificial production of marketable pearls in large 

 quantities should present no great difficulties, if the conditions 

 essential to pearl production in the particular cases be intelli- 

 gently investigated. The fact that trematodes have been 

 ascertained to be at least one cause of pearl formation in several 

 of the molluscs that produce the marketable gems gives us 

 every reason to hope that, by learning the life-hislories of these 

 parasites, we may be able to infect any number of pearl-oysters 

 or pearl-mussels to any desired extent, without any operation 

 on the individual molluscs, by simply placing them in the 

 proper surroundings, in company with infected examples of the 

 first host. Once infected, the molluscs could be bedded out on 

 suitable grounds, and left to care for themselves, until the 

 pearls formed in them were of marketable size. 



These observations show the futility of the proposal that has 

 so often been made, viz., that young pearl-oysters should be 

 transferred from their native grounds to more accessible in- 

 shore waters, as it must obviously be the first object of the 

 scientific expert, before laying down the beds of young pearl- 

 oysters, to assure himself either that they are already infected 

 or that the conditions essential to speedy infection are present 

 on the grounds to which the oysters are to be transplanted. 



H. Lyster Jameson. 



THE MOVEMENTS OF GLACIERS. 



THE study of the movements of glaciers is, we are glad to 

 say, being steadily pursued, judging from the two reports 

 which are to hand. The first is a publication of the Inter- 

 national Commission on Glaciers, and is the seventh report 

 (1901) prepared by Dr. Finsterwalder and M. E. Muret 

 (extract from Archives des Sciences physiques et jiaturelles, t. 

 xiv. , 1902). The report is divided into five parts, dealing with 

 observations made in the Alps of Central Europe, Scandinavia, 

 Spitsbergen and Greenland, Russia and, lastly, the United 

 States. In each case, a brief summary is given of the results of 

 the 1S91 observations published during the past year, and most 

 of these show that, on the whole, the glaciers have decreased in 

 length. 



The second publication contains, not only a report on the 

 variations of French glaciers from 1900 to 1 901, presented to 

 the French Commission by M. W. Kilian, but a review of 

 glaciology, by M. Charles Rabot (extract from the Annuaire du 

 Club Alpin Franeais, vol. xxviii., 1901). Detailed observations 

 are given at some length, and in a few instances reproductions 

 of photographs of glaciers accompany the text. The observ- 

 ations indicate that during this period of time the majority of 

 the glaciers have recoiled or diminished in length. In the 

 second portion of this publication, M. Rabot passes in review 

 the most recent and important works on glaciology, and thus 

 collects a useful number of references to works on this subject. 

 After a brief survey of the physical and geological phenomena, 

 he makes a risumi of the explorations of glaciers in different 

 parts of the earth, pointing out the more interesting facts con- 

 nected with them, and finally gives an account, with numerous 

 references, of the variations of the length of glaciers in different 

 regions. 



THE SCIENCE OF ASTRONOMY? 

 T TAKE for the subject of my address the science of astronomy, 

 *■ and propose to give a brief historical sketch of it, to con- 

 sider its future development and to speak of the influence of 

 the sciences on civilisation. 



The science of astronomy is so closely connected with the 

 affairs of life, and is brought into use so continuously and in 

 such a systematic manner, that most people never think of the 

 long labour that has been necessary to bring this science to its 

 pre-ent condition. In the early times, it was useful to the 

 legislator and the priest for keeping records, the times of public 

 ceremonies and o( religious festivals. It slowly grew into the 

 form of a science and became able to make predictions with 

 some certainty. This was many centuries ago. Hipparchus, 

 who lived 150 K <:., knew the periods of the six ancient planets 

 with considerable accuracy. His periods are : — 



1 Address delivered by Prof. Asaph Hall, on December 2g, 1902, as 

 president of the American Association fvr the Advancement of Sc.ence, 

 Washington meeting. 



Mercury 



Venus 



Earth 



Mars 



Jupiter 



Saturn 



Period 



d. 



87-9698 



224-7028 



365 "2599 



686-9785 



4332-3192 



10758-3222 



NO. 1734, VOL. 67] 



These results indicate that more than two thousand years ago 

 there existed recorded observations of astronomy. Hipparchus 

 appears to have been one of those clear-headed men who 

 deduce results from observations with good judgment. There 

 was a time when those ancient Greek astronomers had con- 

 ceived the heliocentric motions of the planets, but this true 

 theory was set aside by the ingenious Ptolemy, who assumed 

 the earth as the centre of motion, and explained the apparent 

 motions'ofthe planets by epicycles so well that his theory became 

 the one adopted in the schools of Europe during fourteen 

 centuries. The Ptolemaic theory flattered the egotism of 

 men by making the earth the centre of motion, and it cor- 

 responded well with old legends and myths, so that it became 

 inwoven with the literature, art and religion of those times. 

 Dante's construction of Hell, Purgatory and Paradise is de- 

 rived from the Ptolemaic theory of the universe. His ponderous 

 arrangement of ten divisions of Paradise, with ten Purgatories 

 and ten Hells, is said by some critics to furnish convenient 

 places for Dante to put away his friends and his enemies, but 

 it is all derived from the prevailing astronomy. Similar notions 

 will be found in Milton, but modified by the ideas of Copernicus, 

 which Milton had learned in Italy. The Copernican theory 

 won its way slowly, but surely, because it is the system of 

 nature, and all discoveries in theory and practical astronomy 

 helped to show its truth. Kepler's discoveries in astronomy, 

 Galileo's discovery of the laws of motion and Newton's dis- 

 covery of the law of gravitation put the Copernican theory on 

 a solid foundation. Vet it was many years before the new 

 theories were fully accepted. Dr. Johnson thought persecution 

 a good thing, since it weeds out false men and false theories. 

 The Copernican and Newtonian theories have stood the test of 

 observation and criticism, and they now form the adopted 

 system of astronomy. 



The laws of motion, together with the law of gravitation, 

 enable the aslronomer to form the equations of motion for the 

 bodies of our solar system; it remains to solve these equations, 

 to correct the orbits, and to form tables of the sun, moon and 

 the planets. This work was begun more than a century ago, 

 and it has been repeated for the principal planets several times, 

 so that now we have good tables of these bodies. In the case 

 of the principal planets, the labour of determining their orbits 

 was facilitated by the approximate orbits handed down to us by 

 the ancient astronomers, and also by the peculiar conditions of 

 these orbits. For the most part, the orbits are nearly circular ; 

 the planets move nearly in the same plane, and their motions 

 are in the same direction. These are the conditions Laplace 

 used as the foundation of the nebular hypothesis. With ap- 

 proximate values of the periods and motion?, and under the 

 other favouring conditions, it was not difficult to form tables of 

 the planets. However, the general problem of determining an 

 orbit from three observations, which furnish the necessary and 

 sufficient data, was not solved until about a century ago. The 

 orbits of comets were first calculated with some precision. At- 

 tention was called to these bodies by their threatening aspects 

 and by the terror they inspired among people. It was, there- 

 fore, a happy duty of the astronomers to show that the comets 

 also move in orbits around the sun and are subject to the same 

 laws as the planets. This work was easier, because the comets 

 move nearly in parabolas, which are the simplest of the conic 

 sections. Still, the general problem of finding the six elements 

 of an orbit from the six data given by three observations re- 

 mained to be solved. The solution was given by Gauss a cen- 

 tury ago in a very elegant manner. His book is a model, and 

 one of the best ever written on theoretical astronomy. Xo 

 better experience can be had for a student than to come in con- 

 tact with such a book and with such an author. The solution of 

 Laplace for the orbit of a comet is general, but demands more 

 labour of computing than the method of Olbers, as arranged by 

 Gauss. It is said by some writers that the method of Laplace 

 is to be preferred because more than three observations can be 

 used. In lact, this is necessary in order to get good values o. 



