1 66 



NA TURE 



\yuly 2, 1874 



min, edited by J. Norman Lockyer, F.R.S., the fol- 

 lowing note is introduced in brackets by the editor : — 



" The most recent results arrived at \sy geodesists have 

 taught us that the earth is not quite truly represented by 

 an orange, at all events, unless the orange be slightly 

 squeezed, for the equatorial circumference is not a ])er- 

 fect circle, but an ellipse, the larger and shorter 

 equatorial diameters being respectively 41,852,864 and 

 41,843,896 ft. That is to say, the equatorial diameter 

 which pierces the earth from long. 14° 23' east to 194"] 23' 

 east of Greenwich is two miles longer than that at right 

 angles to it."* 



The history of these " results" may be briefly stated as 

 follows ; — 



Capt. Clarke, R.E., in a communic.ition to the Royal 

 Astronomical Society, read April 6, i860, and published 

 in vol. xxix. of the " Memoirs," investigates the figure of 

 the earth resulting from the best existing data. He con- 

 cludes : — 



" The result of our investigations then is this : that the 

 ellipsoid which best represents the existing meridian 

 measurements has its major (equatorial) axis in longitude 

 I3"58''5 east from Greenwich." 



The greatest and least values of the meridian compres- 

 sion are— 

 ^^^ .... ^ - in longitude \f sS'-q E. 



b — c _ _ . . — \ in longitude 103° 58'-5 E. 



c 309'364 



and the length of the polar semi-axis, 20,853,768 ft. '' The 

 difference of the equatorial semi-axis is 5,308 ft., or, in 

 round numbers, just one mile." 



The investigation from which result the above figures 

 was undertaken by Capt. Clarke, in consequence of re- 

 marks by the Astronomer Royal in tlic " Monthly 

 Notices " of the Royal Astronomical .Society, vol. xx. p. 

 104 (January i860), on General Schubert's " Essai d'une 

 dftermination de la veritable figure de la terre." The re- 

 sults arrived at in General Schubert's memoir is that the 

 earth is an ellipsoid, whose elements ate-- 



Polar semi-axis 20,855,605 ft. 



Maximum compression 



292-109 



Compression — , 

 29376 



Minimum „ . . - 



302-004 



Longitude of major axis of equator . . . 4l''4' 22l''4' 

 „ minor axis of equator . . I3i°4' 3ii''4' 

 the longitudes being measured from Greenwich east- 

 wards. 



For the dimensions of the earth on the elliptic hypo- 

 thesis, Capt. Clarke prefers the following values, given at 

 P- 773> of the "Account of the Principal Triangulation 

 (Ordnance Survey)," viz.— 



Equatorial . . 20.926,348 ft. ' 



Polar . . 20,855,233 ft. 



Mean degree . 364,6i3'33ft- 

 The volume was published in 1858. 



It appears, then, that somewhere between long. 13° 

 and long. 41'' east of Greenwich the major equatorial 

 axis is about two miles longer at the present day than the 

 equatorial axis at right angles to it ; and during earlier 

 geological epochs, when the (^ist of the earth was in a 

 more plastic condition, these differences may have been 

 considerably greater, and the effect on the geological 

 s ructure of the earth intensified. 



The point to which I wish to draw the attention of 

 those who have studied the successive variations in the 

 level of certain parts of the earth's surfi.cc, relates to the 

 effect which this equatorial "bulge" must have produced 

 upon various geological phenomena, and particularly if 

 the longitude of the bulge varies according to a determin- 

 able law, 



• Mtm. R.A.S. vol. xxix iSCo. 



It will be readily seen that its influence will be felt— 



1. On the elevation and depression of the land, espe- 

 cially near the equator. 



2. On simultaneous elevation and depression on oppo- 

 sites sides of the earth. 



3. On ocean currents, consequently on climate, &c. 



4. On the thickening and thinning of foriiiations to the 

 east and west. 



5. On the flow of rivers, hence on river and lake ter- 

 races, beaches, &c. 



Observed facts, especially in North America, appear to 

 show that the subsidence and subsequent elevation of 

 that continent has always taken place very gradually and 

 with a progressive motiot\ from west to east and from east 

 to west. In other words, these changes of level have 

 assumed the form of a vast equatorial undulation pro- 

 gressing with extreme slowness, at one epoch in an 

 easterly, and at another in a westerly, direction. This 

 appears to be shown by the very gradual thin- 

 ning out, or the very gradual thickening, of Ter- 

 tiary, Cretaceous, and even Palaeozoic formations. In 

 Post-tertiary times, where we are brought nearer to the 

 records of past changes, and may compare antipodal 

 illustrations, it is apparently manifested by the stupen- 

 dous escarpments which for 1,000 to 1,700 miles rear 

 their wall-like fronts from 200 to 600 ft. above the Onta- 

 rio, Red River, and Saskatchewan plains ; and it is 

 further indicated by the symmetrical river terraces and 

 lake beaches which are developed to a very remarkable 

 extent throughout the whole of the northern part of 

 North America. 



These occur both on the east and west flanks of the 

 Rocky Mountains, and are found in the various passes 

 through that great range. To enumerate examples would 

 be to select any lai-ge river issuing from the Appalachian 

 Chain, the Laurentidcs, or the Rocky Mountains, at ele- 

 vations varying from 400 ft. to 4,000 ft. above the present 

 level of the sea. I hope that some of your correspondents 

 may supply illustrations of similar geological phenomena 

 occurring as near as it may be possible to find records on 

 opposite sides of the earth and during the same geological 

 period of time. 



To the supposed motion of the equatorial bulge may 

 also be partly attributed the changes in the direction of 

 the flow of certain rivers, and the elevation of an axis 

 across the North American continent from east to west 

 between lat. 35° ard 45" N., by which the drainage of the 

 great Canadian Lakes (excepting Ontario) was diverted 

 from the Gulf of Mexico into the Gulf of St. Lawrence. 

 The ancient river channels through which the great lakes 

 sent their waters to the sea are now filled with drift to a 

 depth varying from 200 ft. to 600 ft. During the period 

 of depression the great lakes were in direct communica- 

 tion with the sea, and their waters were brackish or salt. 

 The dredging operations which have been conducted in 

 Lake Michigan show the former m?rine character of the 

 fauna of the waters of this lake. 



The origin of beaches and terraces appears to be inti- 

 mately connected with an easterly or westerly progress of 

 elevation simultaneously with a northerly and southerly- 

 elevation, such as would be produced by the slow move- 

 ment of an eejuatorial bulge in an east or west direction. 

 In North America, where terraces and beaches exist in 

 perfection at altitudes varying, as already stated, from 

 4C0 ft. to 4,000 ft. above the ocean, the phenomena may 

 be studied w-ith some prospect of elucidation. 



I have been credibly informed that data do not at 

 present exist which would enable asti-onomcrs to state 

 definitely that the bulge in the equatorial circumference 

 of the earth between longitudes 13° and 41-' east of 

 Greenwich is stationary, or whether it has an easterly or 

 westerly motion, and thus partakes of the character of an 

 undulation. Peihaps, on consideration of the causes 

 which produce this ellipsoidal form of the equatorial cir- 



