Feb.. 22, 1877] 



NATURE 



361 



and Dr. Jules Carret has just published an ingenious book 

 on the subject.^ 



The paper, of which the following is an abstract, is an 

 attempt to investigate the results of the supposition that 

 the earth is slowly changing its shape from internal 

 causes. The first part is devoted to the mathematical 

 consideration of the precession and nutations of a 

 spheroid slowly undergoing such a change. It is shown 

 that the obliquity of the ecliptic must have remained sen- 

 sibly constant throughout geological history, and that 

 even gigantic polar icecaps cannot have altered the posi- 

 tion of the Arctic circle by so much as three inches ; and 

 this would be the most favourable redistribution of matter 

 for producing that effect. 



But a slow distortion of the earth would displace the 

 principal axis of figure of the earth, and the axis of rota- 

 tion would always sensibly follow the axis of figure. Thus 

 the result would be a change in the geographical position 

 of the poles, without any alteration of the diameters of 

 the arctic circles, or in the width of the tropics. 



For reasons, which cannot be given here, it is main- 

 tained that the earth would not be rigid enough to resist 

 the effects of considerable departures from the figure of 

 equilibrium, such as would arise from a wandering of the 

 pole of figure from its initial position ; and that readjust- 

 ments to an approximate form of equilibrium would pro- 

 bably take place, at considerable intervals of time, im- 

 pulsively by means of earthquakes. Such periodical 

 adjustments would not sensibly modify the geographical 

 path of the principal axis as due to terrestrial deforma- 

 tion. 



The rest of the paper is given to the consideration 

 of the kinematical question of the change in the geo- 

 graphical position of the pole, due to any distortion of 

 the earth. It is assumed, in the first place, that the de- 

 formation is such that there is no change in the strata of 

 equal density ; and accordingly all suppositions as to the 

 nature of the internal changes accompanying geological 

 upheaval and subsidence are set aside. The forms of 

 continents and depressions are investigated, which would 

 cause the maximum deflection of the pole for elevations 

 and depressions of given amounts. 



In order to make numerical application to the case of 

 the earth, some estimate is required of the extent to 

 which it may have become distorted during any one geo- 

 logical period. From the consideration of certain facts, 

 the author believes that from -^ to ^V of the whole earth's 

 surface may have, from time to time, undergone a con- 

 sentaneous rise or fall ; and that the vertical rise or fall 

 may be about 10,000 feet, or rather equivalent to about 

 10,000 feet, when allowance is made for the influx of the 

 sea into depressed areas. 



The first application given in this paper is to conti- 

 nents and seas of the most favourable shapes and posi- 

 tions. It may be here stated that if ^^^ of the earth's 

 surface is elevated by 10,000 feet, the deflection of the 

 pole is 11^' ; if tjV of the whole surface, 1° 46^' ; if ^^, 

 3° 17' ; and if ^, V 4^'.* In each case an equal area is 

 supposed to fall simultaneously. 



Other examples are also given for continents and seas 

 which do not satisfy the maximum condition ; in some 

 the boundaries are abrupt cliffs, in others shelving. 



The conclusion is arrived at that a single large geologi- 

 cal change, such as those which obtain on the earth, is 

 competent to produce an alteration in the position of the 

 pole of from one to three degrees of latitude, on the 

 hypothesis that there is no change in the law of internal 

 density. 



Various other hypotheses as to the nature of the inter- 

 nal changes accompanying the deformation of the earth 

 are discussed. 



I. It is shown that if upheaval and subsidence are due 



I "Le Deplacement Polaire." Savy, Paris, 1877. 



'^ The area of Africa is about "osg, and of South America about "033 of 

 die earth's surface. 



to a shrinking of the earth as a whole, but to the shrink- 

 ing being quicker than the mean in some regions and 

 slower in others, the results are the same as those pre- 

 viously attained. 



2. The increase of surface-matter due to the deposit of 

 marine strata also gives the same results. 



3. The hypothesis that upheaval and subsidence are due 

 to intumescence or contraction immediately under the 

 regions in question is considered. Under certain special 

 assumptions, too long to recapitulate, it is shown that the 

 previous results must be largely reduced. It appears that 

 if the swelling or contracting stratum is tolerably thin and 

 at all near the surface, the deflection of the pole is re- 

 duced to quite an insignificant amount. Even if the 

 intumescence extends right down to the centre of the 

 earth in a cone bounded by the elevated region, the re- 

 sults would be only about 5 of the former ones. Hence 

 it appears that the earlier results can only be stated as 

 the greatest possible for given superficial changes. 



In conclusion it is pointed out that if the earth be quite 

 rigid, no redistribution of matter in new continents could 

 ever cause the deviation of the pole from its primitive 

 position to exceed the limit of about 3°. But if the pre- 

 viously maintained view is correct, that the earth readjusts 

 itself periodically to a new form of equilibrium, then 

 there is a possibility of a cumulative effect ; and the pole 

 may have wandered some 10" or 15° from its primitive 

 position, or have made a smaller excursion and returned 

 to near its old place. No such cumulation is possible, 

 however, with respect to the obliquity of the ecliptic. 



It is suggested that possibly the glacial period may not 

 have been really one of great cold, but that Europe and 

 North America may have been then in a much higher 

 latitude, and that on the pole retreating they were 

 brought back again to the warmth. There seem to be, 

 however, certain geological objections to this view. 



THE NEW STAR IN CYGNUS"- 



ON January 9 the sky was unusually clear and the 

 spectrum of Dr. Schmidt's Nova came out with 

 amazing sharpness and brilliancy. In addition to the 

 five bright lines seen on the 2nd, two others were detected, 

 viz. : — 



Mill. mm. 

 No. la W, L, 594 Very narrow line. 

 ,,7 „ 4I4± Excessively faint, but still certainly and 

 repeatedly seen. 



Between wave-lengths 655 and 594 the spectrum was 

 certainly banded, and, most probably, there were two 

 additional faint maxima of brilliancy in that interval. 

 The continuous spectrum attains a maximum in the 

 region about W. L. 525, and extends, though possibly not 

 without interruption, as far as the faint line No. 7. The 

 star was estimated of seventh magnitude, and was of a 

 red colour with a decided tinge of purple, reminding me 

 forcibly of the varieties of red produced by the quartz- 

 plate in Zollner's photometer. Ralph Copeland 

 Lord Lindsay's Observatory, Dunecht, January 13 



OUR ASTRONOMICAL COLUMN 

 The New Comet. — ^The comet discovered by M. Borrelly, at 

 Marseilles, on the morning of February 9, appears to have been 

 I'ound independently by Herr Pechiile at the Observatory of 

 Copenhagen on the following morning. During the past week 

 it has been making a pretty near approach to the earth, and had 

 the weather been more favourable in Europe, it woild probably 

 have been very generally observed. 



The following elements of the orbit have been calculated by 

 Mr. Hind from the first observation by M. Borrelly, one at 



« Astronomische Nachrichten, No. 2,117. 



