JUNE 25, 1914] 
NATURE 427 
the Thinker,” describing the evolution of his re- 
ligious belief ; “‘ Man the Discoverer and Inventor,” 
treating of the progress of science. ‘The treat- 
ment is essentially popular, and the wide know- 
ledge of the writer, his pleasant style, and his 
skill in weaving into the narrative a store of in- 
teresting allusion and anecdote, render it an 
admirable introduction to the study of anthro- 
pology in its varied aspects. A series of well- 
selected illustrations, including the recently dis- 
covered frescoes in the French caves, with a 
useful bibliography, adds to its interest and value. 
The present revision of the book is, on the 
whole, satisfactory. Detailed discussion of the 
complex problems of the past and future of man 
cannot be expected in a manual. But when men- 
tion is made of “the most ape-like” Piltdown 
skull, we might have anticipated at least a refer- 
ence to the discoveries at Galley Hill and Ipswich. 
Some of the derivations, like those of “ship” and 
“oold” might be improved from Sir J. Murray’s 
Dictionary. If he supposes that the modern Naga 
tribe in India are, like their forerunners of the 
same name, serpent worshippers, he is mistaken; 
and the taboo on the use of dry wood as fuel does 
not extend to the people of Berar, but to a single 
sacred grove. A curious press error gives the 
name of the Hindu sun-god Surya as “Sueya.”’ 
On the whole, this veteran anthropologist is to 
be congratulated on a book which, in its revised 
form, is certain to secure a new lease of popularity. 
The School and College Atlas. One hundred and 
-three maps, physical, political and commercial. 
‘Index. (London: G. W. Bacon and Co., Ltd., 
fed:) Price 35. 6d. ‘net. 
Tuis Atlas is curiously unequal, for it contains 
a mixture of old style and new style maps; some 
maps are overcrowded with names, others are of 
striking simplicity. The summary maps dealing 
with temperatures are in some cases much too 
complicated. The colour-printed maps, showing 
relief on the layer system, indicate by the defec- 
tive fit of the contours how difficult such carto- 
graphic work really is. For an atlas of this size 
the index is much too small. 
The vegetation, annual and seasonal rainfall 
maps should prove of value, and the isotherms for 
the British Isles are based on actual temperatures 
and embody the latest official figures of the 
Meteorological Office. BC. W 
The British Revolution. By Dr. R. A. P. Hill. 
Pp. xii+116. (Cambridge: University Press, 
1914.) tice 25. net. 
Tue most striking feature of most political discus- 
sions is, Dr. Hill considers, an entire lack of first 
principles, and he proceeds to enunciate a “syn- 
thetic” principle,” which he claims stands alone in 
uniting individualism and socialism, home rule 
and imperialism, actuality and the ideal, and many 
other opposed views. He also remarks that one 
of his objects is to supplant Herbert Spencer’s 
synthetic philosophy, or rather to supplement it 
by the principles of the German school. 
NO: 2330; VOL: 93] 
LETIERS, TO; THE EDILOR. 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications. | 
Dynamical Units for Meteorology. 
In the current number of the Quarterly Journal of 
the Royal Meteorological Society I have put forward 
a proposal for a name for a unit of acceleration, and 
shown how the introduction of such a unit leads up to 
the unit of potential which is required in the discus- 
sion of certain problems in aerodynamics. It has 
been suggested to me that as the proposal does not 
concern meteorologists alone it should be canvassed 
in a journal which is read by other physicists. I have 
; written the following notes in the hope that you will 
be able to find room for them in NATURE. 
The convenience of special names for such units as 
the radian, the erg, and the volt, is universally ad- 
mitted. No apology is therefore needed for bringing 
forward a proposal for the adoption of a special name 
for a unit of acceleration. The particular unit for 
which a name is, | think, required is one decametre 
per second per second. This unit is slightly greater 
than the acceleration due to gravity at any point on 
the earth’s surface, but so slightly that there is no 
difficulty in getting a clear conception of it. In this 
way it compares favourably with such units as one 
centimetre per second per second, or one foot per 
second per second. In accordance with the custom of 
honouring the pioneers of science by attaching their 
names to the units which occur in the branches 
which they discovered, it would be natural to name 
the unit of acceleration after Galileo. Unfortunately 
so long a name could not be used in forming com- 
pound names; I propose, however, to preserve the 
association of ideas by calling the unit a “‘leo.” 
Accordingly I define the leo as the acceleration one 
decametre per second per second, 
The acceleration of a falling body due to gravity 
and the earth’s rotation is less than one leo by about 
2 per cent.; the magnitude of the acceleration for 
various latitudes is shown in terms of the leo in the 
following table :— 
Acceleration at the equator 0:9780 leo. 
a in latitude 45° 0-9806 leo. 
i at London 0-9812 leo. 
ee at the poles 0-9832 leo. 
Smaller accelerations may be expressed in terms of 
the same unit or in terms of smaller derived units; 
thus a vehicle which attains a velocity of Io metres 
per second in 10 seconds from rest has an average 
acceleration o-1 leo or 1 decileo. The unit of the 
c.g.s. system, 1 cm./sec.” is, of course, identical with 
the millileo. 
Turning to units of force, we find it natural to call 
the force which gives an acceleration of one leo to the 
mass one gram, a leogram. The leogram is identical 
with the kilodyne, but the new name makes the unit 
easier to realise, as it is seen to be slightly greater 
than the weight of one gram. In the same way the 
names, leokilogram and leoton, speak for themselves 
much better than megadyne and kilomegadyne. 
For pressure, units with simple names, the bar and 
its sub-multiples exist already, but it is mot very easy 
for meteorologists who have not devoted much atten- 
tion to theoretical dynamics to realise the meaning 
of the standard definition 1 bar=1 megadyne per 
sq. cm. Perhaps the phrase 1 leokilogram per sq. cm. 
will be found easier to grasp. The millibar, which 
