JaNuary 8, 1914] 
NATURE 
227 
usual, a prominent place’ is given’ to the bio- 
graphies of eminent British and foreign men of 
science. We know of no more useful work of 
reference, or of one which is consulted more fre- 
quently. : 
(2) This supplement to ‘Who’s Who” con- 
tains a remarkable. miscellany of information as 
to the offices held by distinguished men and so on, 
arranged conveniently in tabular form to assist 
rapid reference. 
(3) With the assistance of an honorary con- 
sultative committee of women workers eminent 
in their respective spheres of activity, the editor 
has compiled an indispensable compendium of in- 
formation for all women who participate in public 
or social life. Parents desiring guidance as to 
careers for their daughters will find this volume 
very helpful. 
(4) The sub-title of this book, “A Directory for 
Writers, Artists, and Photographers ”_exactly 
describes its scope and intention, which are 
fulfilled successfully. 
Papers of the British School at Rome. Vol. vi. 
Pp. xiv+511+xI plates. (London: Macmillan 
and Co., Ltd., 1913.) Price 42s. net 
Tue severely archeological part of this work con- 
sists of reports of excavations in Malta and Gozo 
made in 1908-11, and of a survey of the mega- 
lithic monuments of Sardinia. The investigation 
was confined to Neolithic monuments. Buildings 
usually ascribed to the Phcenicians are now 
assigned to the end of the Neolithic age, or to 
the very beginning of the ‘Eneolithic ” period or 
the age of metals (p. 5). They were “in part 
Sanctuaries, in part dwellings.” No Neolithic 
burials were discovered in them, but typical Neo- 
lithic burials were found elsewhere under other 
conditions (pp. 7, 8, 12). Such evidence fully 
warrants the happy description “megalithic 
sanctuaries” (p. 35). ‘‘Connection of origin with 
the pottery of the AZgean there is apparently 
none; at any rate, it is so remote that we cannot 
trace it, and of direct AZgean influence,” says Mr. 
Peet, ‘‘I can see no certain evidence whatsoever.” 
The builders were evidently allied to the people 
who made “the rock-hewn graves of Sardinia, 
Spain, and perhaps Sicily” (p. 17). 
But the “sanctuaries” of Malta are, according 
to the second report, ‘“‘dolmenic tombs” in Sar- 
dinia. As no evidence of burial is produced, one 
is forced to think that the investigation in that 
quarter is in the ‘‘dolmenic tomb” period of 
research. It is all about the “cult of the dead,” 
with the dead conspicuously absent. In the first 
report Dr. Ashby says: “I do not think that it 
is possible to accept the idea of Evans that these 
mounments ‘served, in part at least, a sepulchral 
purpose.’” (p. 8). 
Excellent plans disclose orientations which rank 
in well-known categories, and the linear measures 
dovetail into striking harmonies, but the “British 
School at Rome” seems to care little for such 
trifles. | Nowhere one finds the suggestion that 
the “sanctuaries” were also observatories. 
Joun Grirritu. 
NO. 2306, VOL. 92] 
} 
LETTERS TO THE EDITOR. 
[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. ] 
The Pressure of Radiation and Garnot’s Principle. 
As is well known, the pressure of radiation, pre- 
dicted by Maxwell, and since experimentally confirmed 
by Lebedew and by Nichols and Hull, plays an im- 
portant part in the theory of radiation developed by 
Boltzmann and W. Wien. The existence of the 
pressure according to electromagnetic theory is easily 
demonstrated,’ but it does not appear to be generally 
remembered that it could have been deduced with 
some confidence from thermodynamical principles, 
even earlier than in the time of Maxwell. Such a 
deduction was, in fact, made by Bartoli in 1876, and 
constituted .the foundation of Boltzmann’s~ work.? 
Bartoli’s method is quite sufficient for his purpose ; 
but, mainly because it employs irreversible operations, 
it does not lend itself to further developments. It 
may therefore be of service to detail the elementary 
argument on the lines of Carnot, by which it appears 
that in the absence of a pressure of radiation it would 
be possible to raise heat from a lower to a higher 
temperature. 
The imaginary apparatus is, as in Boltzmann’s 
theory, a cylinder and piston formed of perfectly 
reflecting material, within which we may suppose the 
radiation to be confined. This radiation is always of 
the kind characterised as complete (or black), a re- 
quirement satisfied if we include also a very small 
black body with which the radiation is in equilibrium. 
If the operations are slow enough, the size of the 
black body may be reduced without limit, and then the 
whole energy at a given temperature is that of the 
radiation and proportional to the volume occupied. 
When we have occasion to introduce or abstract heat, 
the communication may be supposed in the first in- 
stance to be with the black body. The operations are 
of two kinds: (1) compression (or rarefaction) of the 
kind called adiabatic, that is, without communication 
of heat. If the volume increases, the temperature 
must fall, even though in the absence of pressure 
upon the piston no work is done, since the same 
energy of complete radiation now occupies a larger 
space. Similarly a rise of temperature accompanies 
adiabatic contraction. In the second kind of opera- 
tion (2) the expansions and contractions are isothermal 
that is, without change of temperature. In this 
case heat must pass, into the black body when the 
volume expands and out of it when the volume con- 
tracts, and at a given temperature the amount of heat 
which must pass is proportional to the change of 
volume. 
The cycle of operations to be considered is the same 
as in Carnot’s theory, the only difference being that 
here, in the absence of pressure, there is no question 
of external work. Begin by isothermal expansion at 
the lower temperature during which heat is taken in. 
Then compress adiabatically untila higher temperature 
is reached. Next continue the compression iso- 
thermally until the same amount of heat is given out 
as was taken in during the first expansion. Lastly, 
, restore the original volume adiabatically. Since no 
heat has passed upon the whole in either direction, the 
final state is identical with the initial state, the tem- 
1 See, for example, J. J. Thomson, ‘‘ Elements of Electricity and Mag- 
netism " (Cambridge, 1895 § 241): Rayleigh, PAi/. Mag. (xlv., p. 222, 
1898): “* Scientific Papers” (iv., p. 354). , 
* Wied. Ann., vol. xxxii., pp. 31, 291, 1884. _It. is only through Boltz- 
mann that I am acquainted with Bartoli's reasoning. 
