SEPTEMBER 7, 1 8y9} 
NATURE 
4 
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44 
sion of the observations made with the meridian photometer 
during the period 1882-88. The magnitudes, as given in the 
‘Harvard Photometry,” are compared with both the ‘* Urano- 
metria Argentina” and the Boxn Durchmusterung. 4 
For the greater part there is close agreement, but the magni- 
tudes in the Bonn Durchmusterung are found to have a system- 
atic variation according to the right ascension, the stars grouped 
at about R.A. 7h., in the Milky Way near Monoceros, being 
more affected than others also in the Milky Way, but at R.A. 
18-19h., in Aquila. 
Part of the differences between the ‘‘ Harvard Photometry ” 
values and those of the ‘‘Uranometria Argentina”’ are ascribed 
to the difference in position of the two stations, as the zenith 
distances of the stars would be different, and therefore, presum- 
ably, the atmospheric absorption ; no correction being applied 
for this, the southern stars at Cordoba would be estimated too 
bright. 
Aa attempt to revise the scale of the Durchmusterung de- 
cided that it was practically impossible to reduce it to the 
photometric scale by any simple rule, and for purposes of com- 
parison the necessary corrections are given to convert one scale 
into the other from magnitudes 1°o to 9°2. 
Pages 185-233 are devoted to a discussion of the relation be- 
tween the magnitudes in the Harvard Photometry and those 
determined by Sir William Herschel. Of the six catalogues of 
Herschel’s observations, the third is considered more accurate, 
and the fifth less so, than the others. In all he published ob- 
servations of 3000 stars, and the average difference from the 
photometric catalogues of the present day is only +0°16 magni- 
tude, this including both the possible change duzing the century 
which has elapsed and the errors of both 
determinations. Prof. Pickering is sur- 
prised that these observations should not 
have been repeated at intervals of ten or 
twenty years, so that deviations of indi- 
vidual stars might be detected. With this 
idea he gives a special table including all 
stars in which the difference between 
Herschel’s magnitudes and the photometric 
ones equals or exceeds half a magnitude. 
The remainder of the volume, pp. 234- 
245, deals with investigations in regard to 
the relative performance of the large and 
small meridian photometers which have 
been employed in the production of the 
Harvard Photometry itself. No differ- 
ence exceeding the hundredth of a magnitude was detected. 
Tables are given showing that the values of the Harvard 
/ hotometry are not sensibly affected by variations of magnitude, 
right ascension, declination, or proximity to the Milky Way. 
TORSION-STRUCTURE IN THE ALPS. 
ONE of the most brilliant and suggestive chapters in Suess’ 
monumental work ‘‘Das Antlitz der Erde” is that in 
Ss 
Fic. 1.—Formation of fold-arcs under the influence of torsion-forces. 
which he deals with the remarkable whirl shaped arrangement of | 
the leading lines of the Alpine system (vol. i. chap. 2). 
Prof. Suess describes how the ‘‘ leading line” sweeps round 
the northin one great curve convex to the north, the Apennines | 
describe a curve convex towards the east, whereas the 
Dalmatian mountains form opposite it a curve convex to the 
west ; and the curve of the Apennines is continued westward 
along the Algerian ranges of North Africa, whereas the Dalmatian 
curve is continued eastward towards Asia Minor. Prof. Suess 
points out that movements of crust-folding have always. taken 
place towards the convex or outer side of these curves, and have 
in most cases caused an actual transgression of the curves above 
the regions in front of them. He further states that it is not 
fully understood why the mountain-systems should follow curved 
lines, or why the curves of the Alpine upheaval should in many 
areas repeat those of former mountain-systems. 
_Let me, before going further, remind the reader of a lecture 
given by one of the greatest of stratigraphers, Prof. Lapworth, 
at a meeting of the Royal Geographical Society five years ago, 
and reported in these pages (‘‘ The Face of the Earth,” NATURE, 
April 26, 1894). This lecture set forth the conception of crust- 
torsion, demonstrating that ‘‘ like the present surface of a typical 
geological formation . . . the surface of the earth-crust at the 
1 Condensed from the concluding chapter, “Application to the Alps,” in 
a paper presented at the Roy. Geol. Soc., December 1898. 
NO. 1558, VOL. 60] 
present day is most simply regarded as the surface of a con- 
tinuous sheet which has been warped up by the two sets of 
undulations crossing each other at right angles. But in the case 
of the earth-surface, the one set of undulations ranges parallel 
with the equator, and the other ranges from pole to pole.” 
Prof. Lossen’s explanation of the involved stratigraphy of the 
Harz mountains lays the foundation of our knowledge of torsion 
phenomena in the field, and, although other explanations have 
been given of the special difficulties in the Harz mountains, 
Prof. Liéssen’s is now generally accepted. 
When working out the detailed stratigraphy of a part of the 
Dolomites, I experienced the same difficulties which Prof, Suess. 
had indicated in connection with the ‘‘ whirled lines”’ of the 
Alpine system generally. My results were laid before the Geo- 
logical Society in December 1898, and are now published in the 
August issue of the Quart. Journ. Geol. Soc., along witha strati- 
graphical map of the district examined. In that paper I have 
tried to show that the possible solution of some of the difficulties 
lies in the association of torsional movements in conflicting 
directions through the crust, with movements of crust-folding 
taking place across a pre-existing set of crust-folds. The change 
tn the direction of the resultant earth-thrustis the cause to which 
I have ascribed the torsional phenomena observed in the 
crust-folds. : 
The following notes will indicate as briefly as possible where- 
in the characteristic features of Sella and Enneberg in the 
Dolomites are analogous with characteristic features of the 
Alpine system, and how far the elucidation I have offered for 
that area on the lines of torsion may be capable of a wider 
application. 
“ems 
z, areas of interference ; 
v, areas of virgation. 
The stratigraphy of Sella and Enneberg is characterised by 
twisted strikes, twisted cleavages, twisted arches, twisted 
troughs, twisted faults, twisted dykes and sills—in fact, the 
rocks have been twisted and sheared to such a degree that thick 
deposits have been twined into the form of rock-whorls and 
large masses of limestone for the greater part changed to dolo- 
mite. The various combinations of twisted strikes produce the 
effect of ‘* whirled” stratigraphical lines round individual centres 
of the region examined. Sigmoid curves in one direction are 
correlated with sigmoid curves in another, and arcs which are 
convex towards north and south are connected by virgating 
lines with arcs which are convex towards east and west. 
Thus we may say that the curves round the north, east, and 
south of the Sella mountain resemble the ‘‘ whirl-shaped lead- 
ing lines” of the Riviera Alps, Apennines and Algerian moun- 
tains round the western basin of the Mediterranean Sea ; while 
the curves round the north, west, and south of the Pralongia 
and Sett Sass area resemble the whirl-shaped lines of the Dal- 
matian and Pindus mountains and the curvature through the 
eastern basin of the Mediterranean Sea. The latter curvature 
resembles that of the mountains around the Roumanian plain, 
or of the Alps round the plain of Piedmont. 
Examples might be multiplied interminably, and on great and 
small scale, ¢he veason being that the essential structure of the 
Alpine system 7s based upon spirally twisted folds, and not upon 
linear anticlines and synclines. 
The formation of fold-arcs is illustrated in the accompanying 
diagrams (Fig. 1), which show that the action of one torsion- 
couple must be compensated by the reverse action of a corre- 
lated torsion-couple, and a fold-arc convex towards one compass 
direction must be coordinated with a fold-are convex towards 
the opposite compass direction. When the convexities approach 
one another during torsional movements the result is that 
oppositely-curved fold-arcs intertwine in an area which may be 
