August 21, 1919] 



NATURE 



495 



calculated or hypothetic values of mean sea-level over 

 the Baltic area, expressed in terms of deviation (or as 

 isanomalies) from the geoidic surface defined above. 

 It will be seen that these isanomalies are of an order 

 of magnitude far beyond any probable errors in the 

 determination of our base. 



The next step, to be immediately taken, is to com- 

 pare these calculated results with the observed results 

 obtained by actual survey on land, with the most 

 modern niveUetnents de precision achieved by the 

 national Surveys. On this subject Prof. Witting has 

 much to say, and he succeeds in showing that the 

 two sets of results, the calculated and the observed, 

 are wonderfully congruent. For example (and one 

 example must suffice), Prof. Witting arrives by cal- 

 culation at an estimated mean difference of sea-level 

 between Marienleuchte, on the North Sea, and Arkona 

 and Memel, in the Baltic, amounting respectively to 

 +98 and +17 centimetres. The Grerman Prdcisions- 

 nivellierung gives observed values of ii and 17-6 centi- 



^ 



^aA 



3t^ 





Fig. 3.— The mean rate of elevation of the land during the period 1898-19 

 in centimetres per : 



metres. As good, or even better, agreement is shown 

 between stations in the Baltic and Amsterdam, making 

 use of the Dutch as well as the German levellings. 

 In short. Prof. Witting has good right to boast that 

 this part of oceanography has become an exact science, 

 and that his " thalassographic levelling " bears favour- 

 able comparison with, and may even be used to check 

 and to control, the most refined achievements of actual 

 surveys on land. 



The last remaining matter which presents itself is 

 the question of long-period fluctuations of sea-level 

 and the whole subject of secular elevation or depres- 

 sion of the land. Here we start at a disadvantage, 

 from our great ignorance of the variations in level of 

 the ocean itself. But we do know a good deal by 

 observation, and we may learn a good deal more by 

 Prof.. Witting's method of calculation of the relative 

 variations of level at various points of the coast. 

 There is no fixed point which we can designate, but 

 Prof. Witting shows that for about a century the 



NO. 2599, VOL. 103] 



coastal variations in the southern Baltic must have 

 been very small. Suppose, then, that the coast from 

 Wismar to Pillau has, on the whole, kept a constant 

 level ; we may then map out the relative changes over 

 the rest of the Baltic area (as in Fig. 3) during the 

 period of years (1898-19 12) over which Prof. Witting's 

 work extends. The result is striking enough ; but the 

 story does not end there. There are, on one hand, 

 minor fluctuations within the area itself, and some of 

 them are related to seismic phenomena; for instance, 

 there was an interruption in the general upheaval 

 about the time of the Scandinavian earthquake of 

 1904. On the other hand, the phenomena are directly 

 related to those exhibited outside the Baltic area; 

 and it may be said that, though certain minor differ- 

 ences exist — for instance, in Holland — it is clear 

 enough that the Fennoscandian upheaval is only part 

 of a larger movement of the earth's crust, which 

 extends at least as far as the Netherlands and Scot- 

 land. From England the author has to regret that 

 no observations were available. 



With these recent scientific results regarding the 

 elevation of the Baltic coasts Prof. Witting goes on 

 to compare the earlier historic records and the pre- 

 historic evidence, such as it is, which is available 

 from archaeology and from geology. He finds that for 

 some centuries past the elevation of the Fennoscandian 

 lands has gone on at just about the same rate as 

 to-day. The archaeological evidence is more doubtful. 

 It may be that the phenomenon has been approxi- 

 mately the same for some six thousand years; but it 

 was possibly slower during and just after the Bronze 

 age. Prof. Witting suggests — ^and this should interest 

 the archaeologists — that apparent contradictions would 

 disappear if we might assume thaft the older relics are 

 considerably older than Scandinavian archaeologists 

 are accustomed to consider them ; and that, on the 

 other hand, the Bronze age is not quite so old as it 

 is commonly supposed to be. The more ancient pheno- 

 mena are diflficult to discuss, because a damming-up of 

 the Baltic outlet may have produced results not to he 

 distinguished from actual elevation of the lands within. 

 But Prof. Witting believes that in the Littorina period 

 there was certainlv an interruption, and that probably 

 just after the Glacial period there was an acceleration 

 in the rate of elevation. 



Prof. Witting brings a most interesting paper to a 

 close with a strong plea for increased study of sea- 

 levels and all the related phenomena, and for such 

 international co-operation as is obviously essential for 

 a complete and systematic investigation of the whole 

 subject. D'Arcv W. Thompson. 



ENERGY DISTRIBUTION IN SPECTRAA 



OUR knowledge of the structure of very fine spec- 

 trum lines is now on a secure and nearly compre- 

 hensive basis, from the points of view of both theory 

 and of experiment, and it is verj' remarkable that so 

 little is known of the distribution of energy in these 

 lines, either in individual lines or as between the dif- 

 ferent lines contained in the spectrum of any atom. 

 The analysis of the spectra of atoms, theoretically and 

 in the laboratory, is now recognised as the most criti- 

 cal test to which any theory of atomic structure can be 

 subjected, and we have recently had theories of the 

 atom entirely based upon the wave-lengths of the 

 radiations which they emit. A question of equal im- 

 portance, to which i now wish to direct your atten- 

 tion, is the relative amounts of energy which the atom 

 throws out in the form of radiation in the different 



1 Discourse delivered at the Royal Institution on May 2 by Prof. J. W. 

 I Nicholson, F.R.S. 



