May 28, 1886.] 



SCIENCE. 



491 



long chapter of economic history. I think the 

 statement on this point in the body of my article 

 is essentially true. Nor can I agree with my critic 

 that we do not need to stimulate the tendency in 

 this country in favor of state interference. I 

 think that we are prevented to-day from under- 

 taking certain great reforms by the general feeling 

 in the community at large that individual instead 

 of state effort should be relied upon in all cases to 

 secure economic advance. To present the conclu- 

 sion of the matter in a word, it is perfectly possi- 

 ble, of course, for the state to interfere in such a 

 way as to discourage and destroy industry. All 

 of us agree to that. It is, on the other hand, we 

 claim, perfectly possible for the state to interfere 

 in such a way as to promote and create industry — 

 nay, more : it must be continually interfering to 

 do this, otherwise progress would stop and retro- 

 gression set in. Such action is economic in char- 

 acter, and the systematic investigation and discus- 

 sion of it find their proper place in the science of 

 economics. E. J. James. 



CLIMATE AND COSMOLOGY. 



No one should take up Mr. Croll's essays for 

 light reading ; not because his writing is not suf- 

 ficiently clear and concise, but because the inter- 

 action of the many-direct and indirect causes con- 

 cerned in his physical theory of terrestrial climate 

 requires so involved a conception that the reader 

 must go slowly to possess himself of it fully. 

 This is shown by Mr. Croll's frequent and just com- 

 plaint that his critics fail to apprehend his points. 



The essence of his argument is, that, during a 

 time of great eccentricity of the earth's orbit, the 

 hemisphere, having its winter in aphelion, will be 

 subjected to glacial conditions as a result of the 

 various physical processes then brought into play. 

 Prominent among these is the diversion of the 

 warm equatorial ocean- currents into the non- 

 glaciated hemisphere by means of the increased 

 velocity of the trade-winds in the glaciated hemi- 

 sphere, and their extension well across the equator, 

 on account of the then great difference between 

 polar and equatorial temperatures on which they 

 depend. For example : if our hemisphere be the 

 cold one, it is supposed that the north-east trade 

 would gain in strength, and extend south of the 

 equator, so far as to carry all the equatorial cur- 

 rents into the southern hemisphere. " The warm 

 water being thus wholly withdrawn from the 

 northern hemisphere, its temperature sinks 

 enormously, and snow begins to accumulate in 

 temperate regions." 



Discussions on climate and cosmology. By A. Croll. 

 New York, Appleton, 1886. 12°. 



If this fundamental point be conceded, we may 

 as well grant all that follows it ; but it cannot be 

 conceded for a moment. Our north-east trade 

 wall doubtless be strengthened, in winter at least ; 

 but so will the prevailing westerly winds of our 

 temperate latitudes. Moreover, the heat equator, 

 along which the trade-winds meet, will not migrate 

 far south from the geographic equator, on a planet 

 with as short a year, as moderately inclined an 

 axis, and as large an equatorial w T ater-surface, as 

 ours — especially when the southern summer is 

 moderated by coming in aphelion, and again, 

 especially in the Atlantic, as long as the coast-line 

 of Africa allows so much ccol South Atlantic 

 water to reach the central torrid zone, and as 

 long as Cape San Roque stands in the way and 

 turns so much of the equatorial current north- 

 ward. 



No sufficient reason, therefore, appears for 

 granting the north-east trade strength and area 

 enough at such a time to keep warm water out of 

 the North Atlantic, summer and winter ; and in this 

 ocean, at least, the general eddy-circulation would 

 be continued much in its present form, all the 

 more because whatever aid is given by gravity to 

 the wind-made currents is then intensified. The 

 broad drift of waters that crosses the North At- 

 lantic from our shores to Europe would then be 

 accelerated by the stronger winter winds ; it would 

 then, as now, divide opposite Spain ; and the 

 northern branch on which the moderate tempera- 

 ture of north-western Europe so largely depends 

 would then, as now, be supplied largely with 

 water that had been warmed while crossing the 

 equator. As long as this source of warmth pre- 

 vails, a winter's snows in far aphelion cannot over- 

 reach the succeeding summer's melting in close 

 perihelion, without the assistance of geographic 

 or other changes which Mr. Croll deems unessen- 

 tial. 



In view of such objections as this, it seems to 

 me that Mr. Croll decidedly overstates the security 

 of his position in saying that his theory contains 

 ' no hypothetical elements.' The quantitative 

 estimation of his causes is certainly often hypothet- 

 ical. Until more is known, not only about winds 

 and currents, but also about the behavior of the 

 atmosphere towards radiant energy, and the part 

 played by dust over the land (of which Mr. Croll 

 takes practically no account) as well as by vapor 

 over the ocean, there must naturally be much of 

 hypothesis in the discussion of terrestrial tempera- 

 tures. 



Readers of Dr. Croll's work should examine 

 also a critique by Woeikof in a recent number of 

 the American journal of science. 



W. M, Davis. 



