360 



THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



change in the axis of rotation. But it is main- 

 tained that if the earth can yield as a whole, so 

 as to adapt its form to a new axis of rotation, the 

 effects may be cumulative, and that a displace- 

 ment of the pole as much as 10° or 15° is possible. 1 

 But then if the earth be able to adapt its form 

 to a change in the axis of rotation, there is no 

 reason why it may not be able to adapt its form 

 to a change in the rate of rotation, and, if so, the 

 flattening at the poles and the bulging at the 

 equator would diminish as the rate of rotation di- 

 minished, even supposing there were no denuda- 

 tion going on. 



Argument from the Secular Cooling of the 

 Earth. — The earth, like the sun, is a body in the 

 process of cooling, and it is evident that if we go 

 back sufficiently far we shall reach a period when 

 it was in a molten condition. Calculating by 

 means of Fourier's mathematical theory of the 

 conductivity of heat, Sir William Thomson has 

 endeavored to determine how many years must 

 have elapsed since solidification of the earth's 



crust may have taken place. This argument is 

 undoubtedly the most reliable of the three. Nev- 

 ertheless, the data on the subject are yet very 

 imperfect, so that no definite and trustworthy 

 result can be arrived at by this means as to the 

 actual age of the earth. In fact, this is obvious 

 from the very wide limits assigned by him within 

 which solidification probably took place. "We 

 must," quoting Sir William's own words on the 

 subject, " allow very wide limits on such an esti- 

 mate as I have attempted to make ; but 1 think 

 we may, with much probability, say that the con- 

 solidation cannot have taken place less than 

 20,000,000 years ago, or we should have more 

 underground heat than we actually have — nor 

 more than 400,000,000 years ago, or we should 

 not have so much as the least observed under- 

 ground increment of temperature. That is to 

 say, I conclude that Leibnitz's epoch of ' emer- 

 gence ' of the ' consistentur status ' was probably 

 within these dates." i 



— Quarterly Journal of Science. 



THE PLANET OF WAE. 



AMID wars and rumors of war, the planet 

 which has for its symbol the spear and 

 shield of the old Assyrian war-men approaches 

 one of those points of its epicyclic orbit about 

 the earth where it is at its nearest to us. In the 

 earlier part of the Crimean W r ar, Mars shone in 

 our midnight skies, though not so splendidly as 



1 A displacement of the pole of less than 15° or 20° 

 would be of very little service in accounting for the warm 

 climate of Greenland during the Miocene and other periods. 

 But a displacement to that extent, even supposing tiat we 

 admit the earth to be yielding, demands a condition of 

 things which few geologists would be willing to grant. 

 When it becomes generally recognized to what an enor- 

 mous extent the temperature of the arctic regions is de- 

 pendent upon ocean-currents, the difficulties in under- 

 standing how those regions have once enjoyed a temper- 

 ate climate will disappear. Were the ice removed from 

 Greenland that region would at present enjoy a warm 

 summer, suitable for plant and animal life. It is the 

 presence of ice rather than a positive deficiency of heat 

 that makes Greenland so cold and barren (see " Climate and 

 Time," chapter iv.). An increase in the quantity of heat 

 conveyed by ocean-currents, merely sufficient to prevent 

 the accumulation of ice, would completely transform the 

 climate of the arctic lands. And such an increase would 

 take place during an Inter-glacial period when the eccen- 

 tricity of the earth's orbit was at a high value and the win- 

 ter solstice in perihelion. 



he will shine in August and September of the 

 present year. In the early spring of 1854 — 



" .... At a time of the year 

 When the face of night is fair on the dewy downs, 

 And the shining Daffodil dies and the Charioteer 

 And starry Gemini hang like glorious crowns 

 Over Orion's grave low down in' the west," 



the spirit of Maud — 



"... Seemed to divide in a dream from a band 



of the blest 

 And spoke of a hope for the world in the coming 



wars — 



.... and pointed 

 to Mars 

 As he glowed like a ruddy shield on the Lion' s 

 breast." 



The poet expressed the feeling of the day, though 

 the hope of which he sang was not the hope with 

 which men now watch the signs of war. But if 

 Mars were in truth the planet of war, if his influ- 

 ence, poured from near at hand upon the nations 

 of this earth, excited them to war and blood- 

 shed, we might well fear that the coming months 

 would bring desolation on many fair terrestrial 



1 " Transactions of the Eoyal Society of Edinburgh," 

 vol. xxiii., p. 161. 



