March 5, 1908J 



NA TURE 



413 



before Section O at the Leicester meeting of the British 

 A>sociation, and published with illustrations in Engineer- 

 ing^ for August, 11)07, will convey some idea of the ice 

 problem as presented to the users of " white coal " in 

 Canada. In Russia, M. Wladimirop has published several 

 important papers on his studies of the ice conditions on 

 the Neva, in connection with the Waterworks Commission 

 of St. Petersburg. One thing is well established, and that 

 is that the formation of natural ice such as ground-ice, 

 whether in Great Britain, Canada, Russia, France, 

 (jerman\- or elsewhere, conforms to the known knvs of 

 nature. Not a single known case of natural ice formation 

 has ever come under my notice which has not its possible 

 duplication in a laboratory experiment. The two differ 

 onlv in the magnitude of their effects. 



H. T. Baknt.s. 

 Mc(jill LniviTsitv, -Montreal, Februarv lo. 



The Possibility of Life on Mars 



.Mr. Dixes's important letter on the " Isothermal Layer 

 of the Atmosphere " has obviously an important bearing 

 on the question of the gases that have been retained or 

 lost by the atmosphere of Mars. If the temperature of 

 our atmosphere ceases to decrease when a height averaging 

 35,000 feet is reached, and then remains practically 

 constant at an average temperature of —47° C. whatever 

 height be attained, we may expect somewhat similar con- 

 ditions to prevail in the atmosphere of Mars, and naturally 

 ask what are the temperatures which w'ill allow of the 

 escape of the dilTerent gases. 



This question can be easily answered by a brief calcula- 

 tion from the data furnished on pp. 113 and 325 of Jeans 's 

 " Dynamical Theory of Gases " (1904). We find that at 

 a temperature of —175° C. hydrogen will be "certainly 

 retained," while at —65° C. it will be "certainly lost." 

 The corresponding temperatures for helium will be —81° C. 

 and 130° C., and for water vapour 599° C. and 1583'^ C. 

 {■■rom these figures it results that if the temperature of 

 the isothermal layer of Mars be the same as the tempera- 

 ture of that of our atmosphere, hydrogen will be lost, 

 helium probably retained, and water vapour clearly re- 

 tained. I should imagine that in the case of Mars the 

 isothermal layer will be much colder, especially as the 

 carbonic acid that is present in the atmosphere of that 

 planet will be concentrated in the lower levels. 



Neither Prof. Lowell nor Dr. Russel Wallace appear 

 quite to have realised the importance of the influence of 

 carbonic acid on the atmospheric temperature at the surface 

 i)f the planet. 



It is now a commonplace of geology that a variation 

 in the small percentage of carbonic acid in the earth's 

 aDnosphere will have an important effect on the tempera- 

 ture of the latter, though authorities differ as to the 

 numerical amount of the variation required to produce a 

 ijiven change of temperature under given conditions. If 

 the atmosphere contains a relatively large amount of 

 carbonic acid, a correspondingly greater proportion of the 

 heat received will be retained, and the temperature will be 

 higher. Such conditions will be marked by luxuriant 

 vegetation, and at the same time rapid formation of 

 carbonates by the action of water containing carbonic acid 

 on silicates and other minerals. This will eventuate in a 

 period when there is less carbonic acid in the air, and 

 colder conditions will prevail. The growth of vegetation 

 and the decomposition of minerals will be checked and 

 confined to the warmer portions of the earth's surface. 

 The supplies of carbonic acid from intratelluric sources will 

 Then gradually add to the amount of carbonic acid in the 

 atmosphere, bringing an increase in temperature with it.' 

 There are features in the geological record which lend 

 support to the view that such a cvdc of changes has 

 occurred more than once in the earth's history. 



If, now, we make the very reasonable assumption that 

 the crust of Mars is composed of the same minerals as 

 those with which we are familiar, and its atmosphere of 

 the same gases as ours, and that accessions of carbonic 



' I h.ive stated the theory in its simplest tei-ms. There are other circum- 

 stances that aflfcct the amount of carbonic ar: 

 believes that the sea plays an important par 

 gas according to the conditions that prevail. 



n the air. Prof Chamberiil 

 1 absorbing or giving out thi 



acid are received from the interior of the planet, we may 

 expect a similar automatic adjustment of the temperature 

 so that it is never too cold for the chemical reactions of 

 carbonic acid in solution to take place, and for vegeta- 

 tion, such as that believed to exist by Prof. Lowell, to 

 maintain itself somewhere on the surface of the planet. 

 The amount of carbonic acid required for the purpose will, 

 of course, be greater than that in our atmosphere, but 

 there is no reasjn to believe that it would reach an 

 amount which would b"^ injurious to the life of plants or 

 animals, even if such were similar in nature to those on 

 the earth. 



Whether Prof. Lowell can be considered to have estab- 

 lished his views is a question on which I do not feel 

 called upon to express an opinion, but I confess that the 

 arguments advanced against them do not strike me as 

 convincing. They remind me of those of the engineers 

 who satisfied themselves that a locomotive could not draw 

 a train of trucks on smooth rails, and were not persuaded 

 to the contrary until they saw that it did so. 



Imperial Institute, February 28. J. \\". Ev.iNS. 



A Fundamental Contradiction between the Electrical 

 Theory of Dispersion and the Phenomena of 

 Spectrum-series. 



The electrical theory of dispersion is based on the hypo- 

 theses (ij that electric waves are due to motions of electric 

 charges, and waves of light in particular to vibrations of 

 charges inside the atom ; and (2) that these vibrations are 

 governed by linear equations. On this basis we obtain the 

 usual dispersion formula', e.g. that of Drude ; — 



~ tail,, I - \-hlf^^ 

 where 11 is the refractive index for wave-length A, X;, one 

 of the free periods of a set of electrons in the atom, c,, 

 the charge, m,, the mass, and N;, the number per c.c. of 

 the electrons of the set, while the summation is for all 

 possible free periods of the atom. In particular, if \ be 

 greater than every one of the free wave-lengths of the 

 atom, we get 



Consider the contribution of all the lines of the well- 

 known Balmer series to the dispersion of hydrogen ; for 

 this series 



X,, = X^ 



where 



A^ = 



Its contribution exceed 



--4 



= 3646- 13 A. U. 





-4) 



If the theory is to account for the lines of the series 

 at all, the factor N,,e-,,A-.^ /Ttw,, cannot vanish for any 

 line ; let .\ be its least value. Then the contribution 

 exceeds 



A 2 



(;//- - 4)'^ 



The sum is obviously infinite ; but all experience shows 

 that for long waves the refractive index of hydrogen is 

 nearly unity, and finite even for /iimtiiotis hydrogen. 



The same result follows for any series formula which 

 implies that a series has (i) a tail ; (2) an infinite number 

 of lines the wave-length of which exceeds that of the tail, 

 that is, for all known formula? which agree with measure- 

 ments either of line or of band series. 



Thus we must either reject the usual notion of a series, 

 and with it all the formula; which represent our experience 

 best, or we must reject the hypothesis that series lines 

 are due to small vibrations of electric charges governed 

 bv linear equations, and with it the usual theories of 

 dispersion and absorption, of the Zeeman effect and of 

 magnetic rotation for series lines. G. A; Sciiott. 



Phv-ical Institute, Bonn, February 17. 



NO. 200 r, VOL. 77] 



