
ae 
7 
May 26, 1923] 
event at all, but a world-line or chain of events. 
We are then to do the same to a distance CD, and 
so prove the equality of the distances AB and CD. 
_ We are told that in this experiment time is not 
_ vaded by the universal relations. 
involved, and to conclude that in space apart from 
time the test of equality of distance is equality of in- 
terval. Yet the essence of a measuring-scale is its 
permanence in time. We stumble badly over these 
opening paragraphs, and are glad to get on to the 
mathematical developments where all goes smoothly. 
The same confusion of thought, as it seems to us, 
occurs again in the interpretation of Einstein’s law of 
gravitation which is Prof. Eddington’s own (§ 66). 
Einstein’s law is equivalent to the statement that the 
radius of spherical curvature of the three-dimensional 
section of the world at right angles to any direction in 
the four-dimensional continuum has the same constant 
length ./(3/x). A “more precise statement of this 
result ” is said to be that “ the radius of curvature of 
the world at any point and in any direction is in con- 
stant proportion to the length of a specified material 
unit placed at the same point and orientated in the 
same direction.” In this more precise statement the 
word direction is used in the first instance for a direc- 
tion in the four-dimensional world, but “the length of 
a specified material unit placed at the same point and 
orientated in the same direction”’ can only be inter- 
preted as referring to three dimensions. 
We do not raise these criticisms in any captious 
spirit. We believe there is a great deal to be said in 
favour of the general point of view stressed by Prof. 
Eddington that the uniformities revealed in Nature by 
physical experiment would not have been found if our 
physical measurements had not been made with appar- 
atus which is itself part of Nature and is therefore per- 
But the picturesque 
and concise language employed from time to time in this 
book may only too easily persuade the reader that he has 
understood when he has in reality only shirked the issue. 
Thus, after thanking the author for his very complete — 
account of the existing state of the theory and its 
speculative developments, we return almost gladly to 
Prof. Whitehead’s conservatism, and read his chapter on ~ 
some “ Principles of Physical Science.”” We are almost 
grateful for his old-fashioned belief in the funda- 
mental character of simultaneity, adapted to the novel 
outlook by the qualification that the meaning of 
simultaneity may be different in different individual 
experiences. We admire his cautious tread along these 
unexplored paths, and we should welcome him as our 
critic in the task that urgenily needs undertaking, of 
examining the precise position to be allotted to the 
notion of ‘‘ measurement ” in the conceptual universe 
of the relativist. 
NO. 2795, VOL. 111] 
NATURE 
and in the caves of Brazil. 
699 
Fossil Mammals from Bolivia. 
Mammiferes fossiles de Tarija. Par Prof. M. Boule, 
avec la collaboration d’A. Thevenin. (Mission 
scientifique G. de Créqui-Montfort et E. Sénéchal 
de la Grange.) Pp. vii+255+27 planches. (Paris: 
H. Le Soudier, 1920.) 
OR more than three hundred years a great 
accumulation of bones has been known in the 
highlands of Bolivia near the small town of Tarija. 
The bones are scattered in confusion through a deposit 
of sandy mud, the parts of a skeleton rarely in natural 
association ; and they are often well exposed in the 
little ravines which mountain torrents and streams 
have cut through the deposit in all directions. During 
the final years of the last century a large collection of 
the specimens was made by some local residents, 
Messrs. Echazi, and when the Marquis de Créqui- 
Montfort was exploring the country in 1903 he pur- 
chased this collection, and eventually gave it to the 
National Museum of Natural History in Paris. The 
Marquis has now generously provided the means for 
the publication of the handsome volume before us, in 
which Prof. Boule, assisted partly by the late M. 
Thevenin, makes the new discoveries available for 
science. The work is dated 1920, but was only dis- 
tributed last year. 
All the bones in the deposit at Tarija belong to 
‘mammals, most of them large, closely resembling those 
found in the sand and mud of the pampa of Argentina 
They date back either to 
the latter part of the Pliocene or to the early part of 
the Pleistocene period, and are therefore of special 
interest, because they represent the time when the 
mastodons, tapirs, horses, llamas, deer, peccaries, and 
higher carnivores had just come south from the northern 
hemisphere over the newly-emerged land of central 
America, and had mingled with the strange edentates, 
rodents, toxodonts, and macrauchenias which were 
indigenous to South America, and soon became. for 
the most part, exterminated in their rivalry with the 
invaders. Altogether, thirty-five species of large size 
are represented, and their remains are described in 
detail by Prof. Boule, with the aid both of beautiful 
plates in photogravure and of numerous effective text- 
figures. 
The individuals of several species are rather small 
compared with the corresponding forms found in the 
Argentine pampa and other favoured regions, for 
Tarija is at present nearly 2000 metres above the sea, 
and even at the beginning of the Pleistocene period, 
when the elevation was possibly less, the conditions 
cannot have been very genial. When the assemblage 
of animals in question was living in that country, 
