FEBRUARY 14, 1907 | 
NATURE 
369 
stant, is greater than 14; species Q, gases for which 
k is less than 1}. On looking at the page of Naturg 
referred to, it will be seen that Perry questioned or 
even denied the possibility of a gas of species QO. His 
theorem is:—A finite spherical globe of gas, given 
in equilibrium with any arbitrary distribution of tem- 
perature having isothermal surfaces spherical, has 
less heat if the gas is of species P, and more heat 
if of species Q, than the thermal equivalent of the 
work which would be done by the mutual gravita- 
tional attraction between all its parts, in ideal shrink- 
age from an infinitely rare distribution of the whole 
mass to the given condition of density. 
§ 6. From this we see that if a globe of gas QO is 
given in a state of convective equilibrium, with the 
requisite heat given to it, no matter how, and left to 
itself in waveless quiescent ether, it would, through 
gradual loss of heat, immediately cease to be in 
equilibrium, and would begin to fall inwards towards 
its centre, until in the central regions it becomes so 
dense that it ceases to obey Boyle’s law; that is to 
say, ceases to be a gas. Then, notwithstanding 
Perry’s theorem, it can come to approximate convec- 
tive equilibrium as a cooling liquid globe surrounded 
by an atmosphere of its own vapour. 
§ 7. But if, after being given as in §6, heat be 
peepee and sufficiently supplied to the globe of QO-gas 
at its boundary, and the interior be kept stirred by 
artificial stirrers, the whole gaseous mass can be 
brought into the condition of convective equilibrium. 
. In the course of the communication to the 
Royal Society of Edinburgh, curves were shown 
representing the distributions of density and tem- 
perature in convective equilibrium for four different 
gases, corresponding to the four values of k :— 
Gas (1) k=1% (approximately the value of k for 
the monatomic gases, mercury vapour according to 
Kundt and Warburg, argon, helium, neon, krypton, 
and xenon). 
Gas (2) k=1% (approximately the value of k for 
seven known diatomic gases, hydrogen, nitrogen, 
oxygen, carbon monoxide, nitric oxide, hydrochloric 
acid, hydrogen bromide). 
Gas (3) k=1} (approximately the value of k for 
water vapour, chlorine, marsh gas, bromine iodide, 
chlorine iodide). 
Gas (4) k=14 (approximately the value of k for 
sulphur dioxide), 
Four of these curves agree practically with curves 
given by Homer Lane for k=1% and k=12, in his 
original paper to the American Journal of Science, 
July, 1870. 
§ g. In a communication to the Edinburgh Royal 
Society of February, 1387, ‘‘ On the Equilibrium of a 
Gas under its own Gravitation only,’’ I indicated a 
graphical treatment of Lane’s problem by successive 
quadratures, which facilitated the accurate calculation 
of numerical results, and was worked out fully for 
the case k=127 by Mr. Magnus Maclean, with results 
shown in a tabie on p. 117 of the Proceedings of the 
Royal Society of Edinburgh, vol. xiv., and on p. 292 
of the Phil. Mag., March, 1887. The numbers in 
that table expressing temperature and density are 
represented by two of the curves now laid before the 
society. The other curves represent numerical results 
calculated by Mr. George Green, according to a 
greatly improved process which he has found, giving 
the result by step by step calculation without the aid of 
graphical constructions. 
The mathematical interpretation of the solution for 
Perry’s critical case of k=1}, and for gases of the 
Disperies, is exceedingly interesting. 
he communication included also fully worked out 
examples of the general solution of Lane’s problem 
NO. 1946, VOL 75] 
for gases of class P of different total quantities and 
of different specific densities. 
§ 10. In my communication to the Royal Society of 
Edinburgh, of February, 1887, 1 pointed out that 
Homer Lane’s problem gives no approximation to the 
present condition of the sun, because of his great 
average density (1.4). This was emphasised by Prof. 
Perry in the seventh paragraph, headed “Gaseous 
Stars,” of his letter to Sir Norman Lockyer on “The 
Life of a Star” (Nature, July 13, 1899), which contains 
the following sentence :— 
‘“It seems to me that speculation on this basis of 
perfectly gaseous stuff ought to cease when the 
density of the gas at the centre of the star approaches 
0-1 or one-tenth of the density of ordinary water in 
the laboratory.”’ KELVIN. 
THE PROBLEM OF THE RHODESIAN 
RUINS.’ 
ap Be recent investigation of some of the famous 
ruins of Rhodesia, conducted in 1905 by Dr. 
D. Randall-Maclver on behalf of the British Associ- 
ation and the Rhodes trustees, has resulted in an 
entirely fresh view of their origin and age. The 
hitherto generally accepted view, that these buildings 
were erected in very ancient days by a Semitic people, 
whose search for gold led them thus far afield, has 
received a serious check. Dr. Maclver’s researches, 
conducted upon the lines of archzological investi- 
gation, point to the buildings in question being of 
comparatively recent date, not earlier, in fact, than 
late medieval times. This result is the more striking 
when we remember that his previous researches have 
been mainly archeological, conducted chiefly in 
Egypt, and that, in consequence, we might expect a 
certain degree of bias in favour of retaining the ruins 
within the sphere of archeology. That a trained 
archeologist has been unable to find evidence of high 
antiquity upon the sites investigated is at least a 
strong point in favour of his argument. 
Dr. Maclver made excavations on seven sites in 
various parts of Rhodesia, these being :—(1) Inyanga, 
on the Cecil Rhodes estate, sixty miles north of 
Umtali; (2) the Niekerk ruins to the north-west of 
Inyanga; (3) a site three miles south of Umtali; 
(4) Dhlo Dhlo, in the Incisa district; (5) Nanatali, 
sixteen miles east of Dhlo Dhlo; (6) Kami, fourteen 
miles west of Bulawayo; and (7) Great Zimbabwe, in 
the Victoria district, the site which hitherto had re- 
ceived the greatest attention. These sites were well 
selected as being distributed over a wide area, and, 
moreover, as differing considerably from one another 
both in general character and in special features, as 
also in the greater or less degree of elaborateness in 
their structure. It may be remarked at once that the 
distinctive features observable in comparing the 
different buildings are often no less remarkable than 
are the points of similarity. No two seem to be alike, 
and the divergences and specialisation render their 
individuality very striking. 
The principal questions to be determined in regard 
to these remarkable buildings were: By what people 
and at what period were they erected? The contro- 
versy, which is still active, centres mainly upon these 
two main points, and the older theory of their 
Semitic origin and great antiquity, urged by Mauch, 
Bent, Keane, Hall, and others, is being maintained 
steadfastly and strenuously by several authorities. 
Dr. Maclver in the title of his book, ‘‘ Medieval 
Rhodesia,”’ has hoisted his fighting flag. His conten- 
1 “ Mediaeval Rhodesia.’ By Dr. David Randall-Maclver. Pp. xv-+106. 
(London: Macmillan and Co., Ltd., 19¢6. Price zos. net. 
