Sept. ii, 1884] 



NA TURE 



48: 



the equinoxes. We have to consider, therefore, not merely 

 the sidereal year, the time between which the earth is at one 

 point with reference to the sun and a star, and the time when 

 it is at that same point again ; we have not merely to con- 

 sider the fact that this line of solstices, with its conjoined line 

 of equinoxes, varies with regard to what is called the apse 

 line, that is, the line joining the perihelion and aphelion points 

 of the orbit, or the axis-major of the ellipse — but we get from 

 this another year which is called the tropical year, which, like 

 our mean time, is the one most used, because it brings the year 

 into relation with our seasons. Now that we have got our mean 

 time and know exactly how and why we have got it, we may ex- 

 press the sidereal year in mean time, and say that it consists oi 

 365 '256 solar days. The tropical year — the time wjiich elapses be- 

 tween two successive passages through the vernal equinox — is 

 shorter than the sidereal one, owing to the precession along the 

 orbit of the equinoctial points, and consist of 365 '242 mean 

 solar days, and the difference between the lengths of this and 

 the sidereal year will of course give the annual amount of 

 precession which takes place. Anomalistic year is the term 

 applied to tire period which elapses between two successive 

 passages through the perihelion or aphelion points of the orbit ; 

 and as these points have a forward motion along the orbit, this 

 year is longer.than the sidereal one, being 365'259 mean solar 

 days. 



We may give the exact lengths of these years in days, hours, 

 minutes, and seconds as follows : — 



The Movements of the Earth are so important to us, and so 

 interesting in themselves, that it is not possible in six lectures to 

 exhaust all that may be said about them or learned from them. 

 I trust however that I have left no point of the first importance 

 untouched. The moral of these lectures is that astronomy has 

 appealed to physics, and has not appealed in vain, for the de- 

 monstration of the physical reality of the movements in question. 

 J. Norman Lockyer 



THE FRENCH ASSOCIATION FOR THE 



PROGRESS OF SCIENCE 



""THIS Association began its meetings at Blois on September 3. 



The financial situation of the Association is very prosperous 



indeed ; the capital has amounted to 20,000/. ; but the sum 



spent in scientific researches amounts to only 3°° 1 '- 



The President of the Association for this year is M. Bouquet 

 de la Give, and his inaugural address consisted of a sketch of the 

 history of oceanic hydrography. He dealt with the difficulty of 

 the determinations made on the bottom of the sea, and insisted 

 on a new idea of his own. He believes that the level of the sea 

 presents considerable variations owing to the quantity of salt 

 contained in the water. He says that the level of the Mediter- 

 ranean ought not to be so high as the level of the ocean owing 

 to the greater quantity of salt and consequently of density. A 

 diminution of temperature produces the same effects as enlarging 

 the density ; so an increase of the temperature of the German 

 Ocean would produce a flood on the Belgian, Dutch, German, 

 and French coasts, and bring the sea to Paris. 



Dr. Grimaux, a pupil of the late M. Wurtz, delivered a speech 

 on the illustrious Academicians who have died during the past 

 year, among whom Dumas and Wurtz have unquestionably the 

 foremost place. 



It is probable that this year the long-hoped-for fusion with 

 the Association Scientifique de France, established by Leverrier, 

 and presided over by Milne-Edwards, will take place, and the 

 two Associations amalgamated in one will take a new start. 



One of the principal objects of the present sitting has been the 

 examination of the Thenay geological strata, where Abbe 

 Bourgeois thinks he has discovered Tertiary man. The principal 

 French geologists have arrived in Blois for the excursions. 

 There are very few foreigners at the meeting. 



TRAINING IN NA VAL ARCHITECTURE 1 



A T Govan, the great shipbuilding suburb of Glasgow, on the 



•^ 4th inst. , Prof. F. Elgar, of Glasgow University, addressed 



the students attending the Science and Art Classes upon the 



1 Communicated by Prof. Elgar. 



above subject. In the course of his address Prof. Elgar 

 said : — 



"All of the students wh > attend the classes in naval architecture 

 and engineering here are probably much better acquainted with 

 the practical and experimental aspects of the work they are 

 engaged in than they are with the science which underlies it ; 

 and their present object i-; the very vital and praiseworthy one of 

 acquiring such scientific and technical knowledge as will enable 

 them to apply sound principles to the performance of their work, 

 and to assist them in dealing intelligently and successfully with 

 the many difficult and novel questions which are constantly ob- 

 structing and puzzling them. There are no branches of mechani- 

 cal art in which sound scientific knowledge is more essential and 

 useful, or in which it is more necessary for theory and practice to 

 go hand-in-hand together, than those of shipbuilding and en- 

 gineering. A modern steamer is so complex a machine that no 

 attempts to construct one without calling in the aid of science in 

 some form — either directly or by copying what others have 

 learned by it to do — could possibly end in anything but disastrous 

 failure. Try to imagine a man who had never heard or read of 

 any of the teachings of science attempting to construct a modern 

 steamship — a man who did not know even of the proposition,, 

 said to have been demonstrated by Archimedes, that a floating 

 body displaces a volume of water whose weight is equal to its own 

 weight ; and who was ignorant of the wonderful discoveries that 

 have been made of the laws by which heat generated by the 

 combustion of coal is converted into mechanical work through 

 the agencies of the boiler and steam-engine. It only requires to 

 state the matter in this bald form in order to show how hope- 

 lessly impossible and absurd such an attempt would be, and how 

 vitally dependent shipbuilding and engineering are upon the past 

 achievements and present teachings of science. On the other 

 hand, the highest scientific talent the world has yet produced 

 would be equally unable to arrive at a successful result simply l.y 

 means of pure theory, however advanced, and by strict a priori 

 methods. The course you are pursuing, and which I trust you 

 will not depart from, is the one best calculated to insure for you 

 the greatest success in your work and advancement in your 

 various positions in life ; and as in the daily practice of your 

 profession you are perforce kept well abreast of the practical and 

 experimental sides of your work I would now urge you, in the 

 strongest manner possible, to cultivate most diligently and 

 thoroughly a knowledge of the science and of those natural laws 

 upon which the efficiency and success of your efforts depend. 

 Whatever may be the character of your daily work, whether you 

 are employed as engineers, draughtsmen, or mechanics — and I 

 am very pleased to know that there are working mechanics who 

 attend these classes, and who are among the most earnest, in- 

 telligent, and capable of the students — never rest satisfied till 

 you know the meaning of all that you do and why you do it. 

 Do not be content with merely learning methods of setting off 

 work and performing calculations, or with copying processes you 

 may have seen others employ. The man who merely does as he 

 sees others do, without very well comprehending why they do 

 it, and who works strictly by rule and line, looking to custom as 

 the supreme authority, will never improve or advance himself, 

 nor be of much real use in such times as these ; nor will he find 

 much interest in his work. 



' Custom, which all mankind to slavery brings, 

 That dull excuse for doing silly things.' 



Never look to custom as being a sufficient authority for any- 

 thing, however respectable its antiquity may have made it ; but 

 be determined to understand for yourselves whether or not it is 

 based upon sound and intelligible principles. Although we are 

 now meeting under the auspices of the Young Men's Christian 

 Association, I can safely recommend you to indulge freely a 

 spirit of scepticism in this particular department of the Associa- 

 tion's work. The region of science and of the pure intellect is 

 not one in which you should be content to accept the mere 

 authority of any one as final, or to test any question except by 

 the standard of yourl own reason. Do not be too eager 

 to believe that anything you are told is correct until you 

 are able to prove it for yourselves, and till you no longer 

 feel any ignorance or doubt in the matter. The necessity 

 for combining wide scientific knowledge and sound theory 

 with practical experience, in the carrying on of shipbuilding 

 and engineering operations, is daily becoming more and more 

 pressing. If you tried to avoid it you could not. In this 

 age of keen competition and rapid development, increasing de- 

 mands are made upon all who are engaged in these important 



