« PředchozíPokračovat »
EDITORIAL COMMITTEE : S. NEWCOMB, Mathematics ; R. S. WOODWARD, Mechanics ; E. C. PICKERING, As
tronony; T. C. MENDENHALL, Physics ; R. H. THURSTON, Engineering ; IRA REMSEN, Chemistry ; JOSEPH LE CONTE, Geology; W. M. Davis, Physiography; O. C. MARSH, Paleontology; W. K. BROOKS, Invertebrate Zoölogy ; C. HART MERRIAM, Vertebrate Zoology ; N. L. BRITTON, Botany ; HENRY F. OSBORN, General Biology ; H. P. BOWDITCH, Physiology ;
J. S. BILLINGS, Hygiene ; J. MCKEEN CATTELL, Psychology ;
DANIEL G. BRINTON, J. W. POWELL, Anthropology.
FRIDAY, MAY 24, 1895.
Then if the movement of the mass has been
toward the equator the latitude of that CONTENTS :
place is decreased; if toward the pole of Variation of Latitude: J. K. REES.... ....561 the earth the latitude is increased. But Current Notes on Physiography (VII.): W. M. DAVIS...
suppose that some forces at work on the
..568 Gravity Measurements : HERBERT G. OGDEN
earth cause it to revolve about a new The Astronomical and Physical Society of Toronto :
axis, then we have at once a new equator, THOMAS LINDSAY
and the latitudes of all points on the earth's Correspondence:
.575 The Rirers of Eden. J. WILLIAM DAWSON.
surface change except at those places where Color-association with Numerals: E. S. HOLDEN.
the old and new equator intersect. University of Kansas, State Geological Survey : F. H. Snow.
If, for example, the earth's axis of revoluScientific Literature
.577 tion should be changed so as to pass through Nehrling's Native Birds : C. HART MERRIAM
this hall, the latitude would be changed Shau's Municipal Government : J. S. B. Nernst's Chemistry. ROBERT H. BRADBURY. Society from a little over 40 degrees, as it now is, for the Promotion of Engineering Education. R.
to 90 degrees. There are changes no doubt H. T. Steam Power and Millwork: R. H. T. Notes and News :
.581 produced by the slipping of portions of the Joints in the Vertebrate Skeleton: H. F. O. The
earth's strata, but we know that these causes Preparation of Argon: J. E. GILPIN. Helion ; Gravity Measurements ; General.
are insignificant and local. The only way Societies and Academies :
.586 that latitudes could be made to change Scientific Societies of Washington ; The Biological Society of Washington; Boston Society of Natural
throughout the world would be by changes in History; Minnesota Academy of Natural Sciences.
the axis of rotation of the earth, thus changNew Books
ing the position of the equator. MSS. intended for publication and books, etc., intended for review should be sent to the responsible editor, Prof. J.
Are there any undisputed evidences of a McKeen Cattell, Garrison on Hudson, N. Y.
variation in the latitude of a place and is it Subscriptions and advertisements should be sent to SCIENCE, 41 N. Queen St., Lancaster, Pa., or 41 East 49th St., New York.
To-day the evidence is overwhelming, VARIATION OF LATITUDE.*
but the amount is small, so small, in fact, The question is frequently asked, “How that only the refined instruments of the can latitude change?” There are two ways present day have been able to discover it ; obviously. First, we may imagine that a
though now, that it is discovered, older obportion of the earth slips on the surface of servations show it. the globe, due say to earthquake shock. La Place, in his Mécanique Céleste * From a lecture before the New York Academy of
(Tome V., p. 22), says “ All astronomy deSciences, April 29, 1895.
pends upon the invariability of the earth's
axis of rotation and upon the uniformity of places changed several degrees in the course this rotation."
of centuries. These ideas were based on He considered that down to the begin- a comparison of maps made at different ning of this century astronomical instru- times. ments had not been able to show any varia- A disciple of the illustrious Copernicus tion of latitudes. There were differences, considered that the evidence was conclubut these he thought could be accounted sive, and was satisfied that the pole of the for as errors of observation.*
earth was changing its position in a proTo-day, however, we feel certain that gressive manner ; he considered that in time small variations in latitude are taking the torrid and frigid zones would change place, but so small that practically, in map places. making, for example, and in navigation, However, these views of Dominique they are of no importance, though scien- Maria de Ferrare were founded on poor data. tifically very important.
The latitudes of a few places had been deterIt might also, in this connection, be stated mined, by very imperfect means, in the that there are theoretical reasons which best way they had, viz., from the shadow seem to indicate that the earth's rotation cast by a gnomon; but the latitudes of many time is not only changing, but also is not places on the maps were put in from the altogether uniform. The effect of the tide- accounts of travelers, the time it took to wave as it moves west over the earth is to travel from one point to another being used act as a friction-brake on the revolving as the basis of calculation. earth, and so slow up the rotation time, and Even in these enlightened days, as we as this tide effect is not always the same like to consider them, there is no good the retarding effects differ, and theoretically map of our own Empire State. The latiproduce a non-uniformity in the rotation tudes of a few points only in New York time. But the shrinkage of the earth, due State have been determined with accuracy. to loss of heat, would tend to make it re- But there are many places in the State volve more rapidly. These effects may whose positions are not known within more work against each other. However, obser- than a mile. vations and calculations to-day do not fur- In the latter part of the 16th century nish us with any certain evidence that the Tycho Brahe, of Denmark, improved the rotation time is longer or shorter than it instruments in use (without the telescope), was ten centuries ago.
and later, about 1610, the telescope was disIt no doubt will happen that, when ob- covered and applied to astronomical instruservations and instruments are much im- ments. Then new and more accurate proved, astronomers will discover these methods were used to determine latitude, slight changes in rotation time that theory and the large discrepancies disappeared. seems to require.
Some observers found differences between The idea that the latitudes of places latitudes determined in winter and in sumchange is not a new one.
mer, and they supposed those differences to Down to about the time that the tele- be due to changes of the pole. scope was invented there were many learned In the latter part of the 17th century J. persons who believed that the latitudes of D. Cassini summed up the state of the probearth did not change to any large extent ; " We need no brush from a comet's tail to that most of the apparent changes in lati- account for a change in the earth's axis; tude were due to errors of observation and we need no violent convulsions producing defects in theory, but he thought it probable a sudden distortion on a great scale, with that small changes did occur in the position change of axis of maximum moment of of the pole ; he thought the changes were inertia, followed by gigantic deluges; and periodic, and did not amount to more than we may not merely admit, but assert as two minutes of arc equal to about 12,000 highly probable, that the axis of maximum feet. “Thus, instead of several degrees inertia and the axis of rotation, always which were conceded by the astronomers of near one another, may have been in ancient of previous centuries, but a paltry two min- times very far from their present geographutes was now allowed; but with improved ical position, and may have gradually shifted instruments, with the discovery of aberra- through ten, twenty, thirty or forty or more tion and nutation and the perfection of the degrees without at any time any perceptible theory of refraction, even this modest al- sudden disturbance of either land or water." lowance was gradually reduced to a vanish- Sir William Thomson gave no account of ing quantity."
lem in his day, and arrived at the conclu* The writer is much indebted to the paper by Professor Doolittle on "Variations of Latitude' read be
sion that, notwithstanding the apparent fore the A. A. A. S., at Madison, Wis., August, 1893. variations in the latitudes, the pole of the
the calculations made by him as the basis The geologists, in their investigations of these conclusions. have found fossil remains in the cold regions In 1877 Mr. G. H. Darwin made a careof the north, belonging to the Miocene, ful and elaborate mathematical discussion Upper and lower Cretaceous, Jurassic and of the problem. He showed that, in a perother geological periods, which seem to in- fectly rigid globe, the polè could not have dicate a former temperature much higher wandered more than 3 degrees from its than the present. In 1876 Dr. John original position, as the result of the conEvans, then President of the British Geo- tinents and oceans changing places. "If, logical Society, discussed the problem, and however, the earth is sufficiently plastic to concluded that the amount of polar light admit of readjustment to new forms of and heat in the past must have been much equilibrium, by earthquakes and otherwise, greater than it is now. He invited the at possible changes of ten or fifteen degrees tention of the mathematicians to this prob- may have occurred. This would require, lem, and asked : Would a considerable ele- however, such a complete changing about vation and depression of the sea bottoms and of the continents and oceans, with maximum continents produce a 'change of 15 degrees elevations and depressions in precisely the to 20 degrees in the position of the pole?' most favorable places, as has certainly never
Sir William Thomson discussed this occurred in geologic times.” problem and gave his conclusions in 1876 The evidence indicates, in fact, that the to the British Association for Advancement continental areas have always occupied of Science. He said: “ Consider the great about the same positions as now. facts of the Himalayas and Andes and Thus it would seem that the geologists Africa, and the depths of the Atlantic, and must abandon the hypothesis of great America and the depths of the Pacific, and changes in latitude as a factor in the earth's Australia; and consider further the ellip development, unless a new cause can be ticity of the equatorial section of the sea found that will move the pole to the extent level, estimated by Colonel Clarke at about required by the geologists. one-tenth of the mean ellipticity of the In an address made before Section A, of meridianal sections of the sea level.
the British Association in 1892, Professor Shuster stated that he believed the evidence to work in conjunction with the Naples Obat hand was in favor of the view that there servatory on the problem. This series of was sufficient matter in interplanetary space observations was begun in the spring of to make it a conductor of electricity. This 1893, and will be continued several years. conductivity, however, must be small, for if The data given by Fergola at Rome in it were not, he said, the earth would gradu- 1883 showed a diminution of latitude in ally set itself to revolve about its magnetic every case; other data showed a similar poles. However, changes in the position of diminution ; however there were excepthe magnetic poles would tend to prevent tions, where the latitudes seemed to inthis result. Perhaps the investigator in the crease. near future, working on the suggestion of The investigations that have been going Dr. Shuster, may find some connection be- on since 1883 throw doubt on the progressive tween the earth's magnetism, rotation time changes in latitude, or at least such changes and position of rotation axis.
are masked by proved periodic changes. The evidence, then, at this phase of the For a long time, since 1765, periodic discussion, is in favor of the view that there changes have been looked for, because the is no adequate reason for believing that any theory of a rotating earth, an earth havlarge changes of latitude, amounting to sev- ing the form of a sphere flattened at the eral degrees, have occurred in geologic poles, or, more accurately, an ellipsoid of times. The evidence shows, however, that revolution, demanded such changes ; but there are small changes. Are they progres- the theory did not furnish any clue to the sive; does the north pole of the earth wan- amount of changes, except that they must der slowly but surely further and further be very small. This theory shows that if away from its positions of ages gone by? the earth was absolutely rigid and revolved
At the International Geodetic Congress about its shortest axis (called the axis of held in 1883 at Rome, Sig. Fergola, of the figure) at any time it would continue to Royal Observatory Cappodimonti, Naples, revolve about such axis forever, unless disgave a tabular statement which seemed to turbed by some outside force. If so disshow that small but progressive changes had turbed, then the axis of rotation would no taken place in Europe and America. This longer coincide with the axis of figure—the table showed, for example, that the latitude of axis of rotation would intersect the earth's Washington, D. C., had decreased from 1845 surface at points away from the points to 1865, 0.47" ; at Paris, from 1825 to 1853, where the axis of figure comes out. But the decrease was 1.8"; at Milan in 60 years, the theory also showed that the new axis 1.5"; at Rome during 56 years, 0.17"'; at of rotation would revolve about the old one Naples in 51 years, 0.22''; at Königsberg in in a period of 304.8 days. This period 23 years, 0.15''; at Greenwich in 19 years, comes from the knowledge of the magni0.51". Fergola, at the Congress mentioned, tude of precession and nutation, and is suggested a plan for making systematic ob- known very accurately. servations, and he pointed out the favora- We would expect therefore that changes ble location of several observatories that in latitude would show this 305-day period. were on nearly the same circle of latitude, Several attempts have been made to debut differing widely in longitude. Unfor- termine the distance between the two axes tunately this suggestion of Fergola's was (figure and rotation axis) from changes in not carried out in any way until 1892, when latitudes. the Columbia College Observatory arranged The celebrated astronomer Bessel made
the first attempt, and was unsuccessful, it to determine the separation of the axis of was supposed until recently.*
rotation and axis of figure, were going on Observations were also made at Pulkova, that Sir Wm. Thomson (now Lord Kelvin) Russia, Greenwich and Washington. The announced, at the Congress of the British Washington observations were made be- Association at Glasgow in 1874, that the tween 1862 and '67, and included six complete meteorological phenomena, the fall of rain periods of 305 days each. A rigorous dis- and snow, the changes which occur in the cussion by Newcomb gave the separation circulation of the air and of the sea waters of the axes as 3 feet, or 0.03".
would modify a little the mechanical conC. A. F. Peters, of Pulkova, had in 1842, stitution of the globe, and displace a little obtained ".079 = 8 feet.
the axis of figure, i. e., the form of the These figures are small, but fairly accord- earth would be changed by the causes menant. A reinvestigation, however, showed tioned, and so a new shortest axis would that the various calculations did not agree be made. The effect of this would be to in showing the same displacement at the produce a change in the latitudes of places, same time.
This made the whole result evidently. He thought that it might doubtful, so that Newcomb (in 1892, March, amount to ".50, which would correspond Mon. Not. R. A. S.) remarked that “the to a movement of the old axis (at the pole) observations showed beyond doubt there of 50 feet on the earth's surface. Sir W. could be no inequality of the kind looked Thomson did not publish his calculation, for."
but the authority of the great English It was while investigations of this kind, mathematician and physicist was such as to
make scientific men give the statement * Tisserand says in Ann. Bur. Long. '95 (P. 42,
great attention. These meteorologic pheB. 11) that there is a letter of April 7, 1846, in which Humboldt replies to Gauss that Bessel had told him
nomena of which Sir William Thomson in 1844 that his observations showed that his latitude spoke are annual in character. When this had decreased 0. 3'' in two years. Bessel attributed annual period is combined with the 305this variation to changes accomplished in the interior
day or ten-month period of Euler we see of the globe. See also Hagan's letter in Astr. Nach.,
that complexity results. This was the September, 1894. In this connection it ought to be noted also that
state of the investigation when Dr. KüstProf. J. C. Maxwell read a paper April 20, 1857,
ner, of the Berlin Observatory, published the before the Royal Society of Edinburgh (see Transac- results of his observations made in 1884tions Roy. Soc. Edinburgh, Vol. XXI., Part iv., pp.
1885. Dr. Küstner undertook some obser559–571), 'On a Dynamical Top for exhibiting the
vations for the trial of a new method for phenomena of the motion of a system of invariable form about a fixed point, with some suggestions as
the determination of the constant of aberto the earth's motion.' He deduced a period of 325.6 ration. On reducing his observations he solar days. He examined the observations of Polaris obtained results which were not at all satmade with the Greenwich Transit Circle in the years isfactory. A careful examination of his 1851-54. He found the apparent co-latitude of Greenwich for each month of the four years specified.
work led him to make the announcement “There appeared a very slight indication of a
that the unsatisfactory value for the aberramaximum belonging to the set of months, March, '51;
tion constant was due to a comparatively February, '52; December, '52; November, '53; Sep- rapid, though very small, change in the lattember, '54." This result, he says, “is to be re- itude of the Berlin Observatory—“that from garded as very doubtful, as there did not appear
August to November, 1884, the latitude of be evidence for any variation exceeding half a second of space and more observations would be required to
Berlin had been from ".2 to ".3 greater than establish the existence of so small a variation at all.” from March to May in 1884 and 1885.”