August 31, 1905] 



NA TURE 



445 



round the sun under the action of solar gravitation. The 

 success of the liypothesis of stellar gravitation has been 

 so complete that astronomers have not hesitated to explain 

 the anomalous motion of a seemingly single star by the 

 existence of a dark companion ; and it is interesting to 

 know that the more powerful telescopes of recent times 

 have disclosed, in at least two cases, a faintly luminous 

 companion in the position which had been assigned to it 

 by theory. 



By an extension of the same argument, certain variations 

 in the spectra of a considerable number of stars have 

 been pronounced to prove them each to be really double, 

 although in general the pair may be so distant that they 

 will probably always remain single to our sight. Lastly, the 

 variability in the light of other apparently single stars 

 has proved them to be really double. A pair of stars may 

 partially or wholly cover one another as they revolve in 

 their orbit, and the light of the seemingly single star 

 will then be eclipsed, just as a lighthouse winks when the 

 light is periodically hidden by a revolving shutter. Exact 

 measurements of the character of the variability in the 

 light have rendered it possible not only to determine the 

 nature of the orbit described, but even to discover the 

 figures and densities of the two components which are 

 fused together by the enormous distance of our point of 

 view. This is a branch of astronomy to which much 

 careful observation and skilful analysis has been devoted ; 

 and I am glad to mention that Alexander Roberts, one of 

 the most eminent of the astronomers who have considered 

 the nature of variable stars, is a resident in South Africa. 



I must not, however, allow you to suppose that the 

 theory of eclipses will serve to explain the variability of 

 all stars, for there are undoubtedly others the periodicity 

 of which must be explained by something in their internal 

 constitution. 



The periods of double stars are extremely various, and 

 naturally those of short period have been the first noted ; 

 in times to come others with longer and longer periods 

 will certainly be discovered. A leading characteristic of 

 all these double stars is that the two companions do not 

 differ enormously in mass from one another. In this 

 respect these systems present a strongly marked contrast 

 with that of the sun, attended as it is by relatively in- 

 significant planets. 



In the earlier part of my address I showed how theory 

 indicates that a rotating fluid body will as it cools separate 

 into two detached masses. Mathematicians have not yet 

 been able to carry their analysis far enough to determine 

 the relative magnitudes of the two parts, but so far as we 

 can see the results point to the birth of a satellite the 

 mass of which is a considerable fraction of that of its 

 parent. Accordingly See (who devotes his attention largely 

 to the astronomy of double stars), Roberts, and others 

 consider that what they have observed in the heavens is 

 in agreement with the indications of theory. It thus 

 appears that there is reason to hold that double stars 

 have been generated by the division of primitive and more 

 diffused single stars. 



But if this theory is correct we should expect the orbit 

 of a double star to be approximately circular ; yet this is 

 so far from being the case that the eccentricity of the 

 orbits of many double stars exceeds by far any of the 

 eccentricities in the solar system. Now See has pointed 

 out that when two bodies of not very unequal masses 

 revolve round one another in close proximity the conditions 

 are such as to make tidal friction as efficient as possible 

 in transforming the orbit. Hence we seem to see in tidal 

 friction a cause which may have sufficed not only to 

 separate the two component stars from one another, but 

 also to render the orbit eccentric. 



I have thought it best to deal very briefly with stellar 

 astronomy, in spite of the importance of the subject, 

 because the direction of the changes in progress is in 

 general too vague to admit of the formation of profitable 

 theories. 



We have seen that it is possible to trace the solar system 

 back to a primitive nebula with some degree of confidence, 

 and that there is reason to believe that the stars in 

 general have originated in the same manner. But such 

 primitive nebulae stand in as much need of explanation 



NO. 1870, VOL. 72] 



as their stellar offspring. Thus, even if we grant the 

 exact truth of these theories, the advance towards an 

 explanation of the universe remains miserably slight. Man 

 is but a microscopic being relatively to astronomical space, 

 and he lives on a puny planet circling round a star of 

 inferior rank. Does it not then seem as futile to imagine 

 that he can discover the origin and tendency of the 

 universe as to expect a housefly to instruct us as to the 

 theory of the motions of the planets? And yet, so long 

 as he shall last, he will pursue his search, and will no 

 doubt discover many wonderful things which are still 

 hidden. We may indeed be amazed at all that man has 

 been able to find out, but the immeasurable magnitude 

 of the undiscovered will throughout all time remain to 

 humble his pride. Our children's children will still be 

 gazing and marvelling at the starry heavens, but the riddle 

 will never be read. 



SECTION E. 



GEOGRAPHY. 



Opening Address by Rear-Admiral Sir W. J. L. 

 Wharton, K.C.B., F.R.S., President of the Section. 



It is sometimes denied to Geography that she has any 

 right to consider herself as a science, the objection being 

 apparently founded on the view that it is a subject that 

 can be learnt by heart, but not studied on any systematic 

 line or reduced to principles which enable advance to be 

 made, as in the more exact sciences, by continual in- 

 vestigation by means of laws discovered in the course of 

 such investigation. This, it appears to me, is a misap- 

 prehension due to an incomplete recognition of what 

 Science is, and of what Geography is. 



Science is, in its simplest interpretation, " knowledge," 

 such knowledge as comes from an intimate acquaintance 

 with and study of any subject duly coordinated and ar- 

 ranged. The subjects which the advancing education and 

 civilisation of the world have caused to be minutely studied 

 are very many, and as knowledge has increased specialisa- 

 tion has become a necessity, until the list of sciences is 

 very long. 



Science may be broadly divided into several categories. 



Pure or Exact Science, such as Mathematics ; Natural or 

 Physical Science, which rests on observations of Nature ; 

 Moral Science, which treats of all mental phenomena. 



Some Sciences are of ancient foundation, some have 

 arisen from new inquiries and needs of man, or from 

 fissure in subjects too wide for convenient treatment as 

 one. 



Many of them are capable of exact definition, and their 

 boundaries and limits can be well marked. 



To others no very distinct limitations can be assigned. 

 From their nature they overlap and are overlapped by other 

 subjects, and it is impracticable to confine them by a strict 

 line. 



Geography is one of the latter. 



Geography is one of the most ancient subjects studied 

 with the view of coordinating facts, k desire for exact 

 knowledge of, first, the bearings and distances of one 

 place from another for the purposes of intercommunication 

 must have arisen as soon as men became collected into 

 groups whose growing civilisation and needs required 

 travel to obtain what could not be obtained in the com- 

 munity. This was the earliest form of Geography, and 

 it is an aspect which still remains, and to some is, in the 

 modern shape of maps, the principal, if not the sole, end 

 of Geography. 



Froni the earliest times, however, geographical informa- 

 tion included other than topographical data. 



It was soon found that for the traveller and statesman, 

 whether in peace or war, more was wanted to enable 

 Geography to supply requirements. 



The nature of a country, the supply of food and water, 

 the characters of the rivers, the manners and customs of 

 the inhabitants, their language and affinities, the climate, 

 and other matters, were all of much moment, and Geo- 

 graphy dealt with them all, being, as its name denotes, 

 in the broadest sense a "description of the earth." 



After the first crude guesses of relative positions, 



