September 7, 1893] 



NA TURE 



451 



VARIATIONS OF LATITUDE > 



"ALL astronomy," says Laplace, "depends upon the in- 

 ■'*■ variability of the earth's axis of rotation upon the terres- 

 trial spheroid and upon the unifonuity of this rotation." He 

 adds that "since the epoch when the application of the 

 telescope to astronomical instruments gave the means of observ- 

 ing" terrestrial latitudes with precision, no variations in such 

 latitudes have been found which could not be attributed to errors 

 of observation, which proves that since this epoch the axis of rota- 

 tion has remained very near the same point on the terrestrial sur- 

 face." ("Mecanique Celeste," tome v. page 22.) Admitting then 

 the position of the earth's axis, and consequently the values of 

 terrestrial latitudes, to be sufficiently invariable for the purposes 

 of the astronomer, the question has been many tines raised 

 whether this conclusion represents more than a kind of first 

 approximation to the truth. 



As this subject, or something very much like it, was receiv- 

 ing more or less attention on the part of the ancient geographers 

 two thousand years ago or more, we can hirdly claim for it the 

 charm of novelty, kn important feature of the geography of 

 Eratos Thenis, written between 200 and 300 B.C., was a critical 

 review of the work of his predecessors. His map of the world, 

 which represented the best and latest information of his day, had 

 as a sort of base line, or axis of reference, a parallel of latitude 

 drawn from the pillars of Hercules towards the east, passing 

 north of the island of Sicily, across the southern part of the 

 Peloponnesus, and eastward across the continent of Asia. The 

 positions of many places with reference to this line differed very 

 considerably from those assigned by his predecessors. At the 

 time of Ptolemy — 400 years later — it was known that the map 

 of Eratos Thenis failed in many particulars to conform to the 

 then existing order of things. The conclusion was obvious ; 

 evidently changes had taken pLace in the relative positions of a 

 number of prominent places on the earth ; nor were these changes 

 simply the trifling fractions of a second with which men are 

 struggling so valiantly in these degenerate days, but such satis- 

 factory and tangible quantities as three, four, or five degrees. 

 P.olemy's geography furnished the basis for comparisons and 

 discussions of this kind for fifteen hundred years. Some few of 

 his latitudes, as that of Alexandria, were determined with such 

 precision as was possible in those days, while the foundation of 

 very many was little more than guess-work. Comparisons from 

 time to time with later determinations brought to light discre- 

 pancies which served to keep the question open and to furnish 

 material for speculation. 



In this connection we shall stop only to mention Dominique 

 Maria de Ferrare, who enjoys>the distinction of having had as 

 a disciple the illustrious Copernicus. This philosopher believed 

 that the evidence showed conclusively a progressive change in 

 the pwition of the pole, and that in time the torrid and frigid 

 regions would in a manner change places. 



Sj far as the latitudes of Ptolemy were concerned it was 

 pointed out- that the discrepancies were in part due to the 

 method employed in their determination — that of the gnomon 

 which gave the altitude of the sun's upper limb, and conse- 

 quently a value of the latitude too small by a quarter of a 

 degree. 



Two or three hundred years ago much interest was taken in 

 this question. We find associated with it the familiar names of 

 Tycho, Rcemer, Hevelius, Picard, Cassini, and many others. 

 As greater accuracy in methods and instruments prevailed, it 

 became evident that the rough poiitions of Ptolemy could not 

 be employed with any confidence in discussions of this character. 

 In connection with the e more exact methods also a new phe- 

 nomenon began to manifest itself, viz., changes of short 

 period. 



Christopher Rothman, a contemporary of Tycho, found 

 systematic differences between the determinations of the 

 latitude of his observatory made in summer and winter. Tycho's 

 observations at Prague showed a like peculiarity. Roe.ner also 

 discoverel it. He :ittributed it confidently to periodic changes 

 in the position of the eaVth's axis, and hoped in time to give a 

 complete theory of the same. 



A memoir by J. D. Cassini,' published in 1693 — 200 years 



1 AdJres^ before Section A (,\stron':>my) of the American A^isociation for 

 ttie Advancement of Science, at Madis m, Wisconsin, by Prof. C. L. 

 Doolitlle, of Sjuih Bethlehem, Pa., President of the Section. 



2 Delanibre, " Histo're de I'Asironomie au D!x-huiticine S ccle,''p. 155. 



3 S'il est arrivf^ dii chanj^e n nt :an<i Lautein du pole au dans la (Jones du 

 Sofeil. f^M^moires de V Aciuieif.i:, tjme x. p. 360.) 



NO. 1245, VOL. 48] 



ago almost precisely — gives a very complete summary of 

 the state of the problem at that day. After a detailed 

 examination of the evidence he concludes : — " Notwithstanding 

 all these apparent variations, we may say that iiot only has no 

 extraordinary change in the altitude of the pole or in the meridian 

 altitude of the sun occurred in recent times, but that the 

 heavens have at all times occupied the same position with regard 

 to the earth as during the past century. For there is reason to 

 believe that all these variations which have been mentioned 

 came from several defects which occur in observation." He 

 then goes over in detail those sources of error which are so 

 familiar to us — instrumental errors and defects in theory — one 

 only having a somewhat unfamiliar appearance, viz., we may 

 reasonably suppose that variations in the direction of the plumb 

 line occur similar to those of the magnetic needle. Nevertheless 

 he says it is very probable that from time to time small changes 

 in the altitude of the pole actually do occur, but they are periodic 

 in character and do not exceed two minutes in amount. Thus, 

 instead of several degrees which were conceded by the astrono- 

 mers of previous centuries, only a paltry two minutes was now 

 allowed, but with improved instrumints, with the discovery of 

 aberration and nutation, and the perfection of the theory of 

 refraction, even this modest allowance was gradually reduced 

 to a vanishing quantity. 



Meanwhile new arguments were found for a reconsideration 

 of the question. Geology had taken its place among the sciences. 

 In the investigation of the fossil remains of plant and animal 

 life abundant evidence was found of a former temperate or sub- 

 tropical climate within the Arctic circle. It was also evident 

 that at one time considerable portions of Europe and North 

 America had been covered with glacial ice. Laplace mentions 

 the argument for a change in the position of the earth's axis, 

 founded on the existence of the fossil remains of elephants in 

 Northern Siberia, but believes that the discovery of the remains 

 of one of these animals preserved in ice, the body of which was 

 covered with thick hair, turns the argument against those who 

 employ it (M.C. v. p. 20). 



In the Quarterly lournal of the Geological Society for 1848 

 is found a communication from a mathematician and astronomer. 

 Sir John Lubbock, on changes in climate resulting from changes 

 in the earth's axis of rotation. He suggests a mathematical dis- 

 cussion of the problem in order to determine, as he says, " under 

 what hypothesis a change of the position of the axis of rotation 

 is possible or not. " The President of the Association, Sir Henry 

 T. de la Beche, in the annual address of 1849, deals at some 

 length with this subject. Again, in 1876, we find Sir T')hn 

 Evans, then president of the Society, discussing the problem 

 {^Quirterly Journal of the Geological Society, 1876, p. 60). He de- 

 scribes with much detail the fossil remains found in Spitzenbergen 

 and Greenland belonging to the Miocene, upper and lo^yer 

 Cretaceous, Jurassic, and other geological periods, all of which 

 point to a former temperature much above the present. Thus, 

 among the Miocene plants of Spitzenbergen Prof. Nordenshiiild 

 mentions the swamp cypress, now found in Texas, siqiioias of 

 great size, limes, oaks, and even magnolias. So in the 

 L)wer Cretaceous period Prof. O. Heer distinguished seventy- 

 five specie.s, including ferns, Cycadese and Coniferre, many of 

 which are closely allied to species now found in sub-tropical 

 regions. From these remains Prof. Heer infers that the climate 

 of Greenland and Spitzenbergen during the Cretaceous period 

 was very much the same as that which now prevails in Egypt 

 and the Canary Isles. The existence of beds of coal, of 

 mountain limestone formed of the remains of corals and bryozaa, 

 and shells of marine molluscs, the remains of Ammonites, 

 Nautili, and even a Saurian— the Ichthyosiurus polaris—M 

 point in the same direction. While, as Prof. Houghton remarks, 

 the arguments from the presence of Ammonites and Coalplants 

 strengthen each other, the one demanding heat, the other light. 



Sir John Evans sums up the arguments as folloivs : — " The 

 three points which it appears to me are most important to bear in 

 mind with regard to the article of flora are (l) that for vegetation 

 such as has been described there must, according to all analogy, 

 have been a greater aggregate amount of summer heat supplied 

 than is now due to such high latitudes.- (2) That there must 

 have been a far less degree of winter col 1 than is in any way 

 compatible with ihi position on the globe ; and (3) that in all 

 probability the amount and distribution of light which at pre- 

 sent prevail within the Arctic circle are not such as would suffice 

 for the life of the trees." 



He afterwards supposes a hypothetical case of posiible 



