August 27, 1886.] 



SCIENCE. 



189 



contrast will appear very striking to any one who 

 will compare the maps of January and July iso- 

 therms, respectively, for the globe. The two maps 

 will be seen to differ but slightly in the southern 

 hemisphere, immensely in the northern. I know no 

 reason why a contrast between extremes and means 

 in climate, produced by geographical conditions, 

 should have a materially different effect, as regards 

 glaciation, from a like contrast produced by astro- 

 nomical conditions. It appears, then, that a com- 

 parison of the northern and southern hemispheres 

 may show us whether a climate of means or a climate 

 of extremes is favorable to glaciation. 



Now, there can be no doubt that at present the 

 southern hemisphere is suffering a greater degree of 

 glaciation than the northern. As the facts are so 

 well known, it is only necessary to allude to them. 

 New Zealand, with a mean temperature about the 

 same as that of Switzerland, has glaciers extending as 

 nearly to the sea-level as those of Norway.' Nor is 

 this due to any exceptionally large snow-fall in New 

 Zealand, for the precipitation there is no greater 

 than in Norway, and considerably less than in Swit- 

 zerland. Tierra del Fuega, with a mean temperature 

 about equal to that of southern Norway, and with a 

 winter temperature no colder than that of Switzer- 

 land, has glaciers extending to the sea.^ The same 

 is true of the island of South Georgia, if, indeed, 

 perpetual snow does not descend to the level of the 

 ocean (as reported by Captain Cook).^ 



It may, I think, fairly be concluded that glaciation 

 depends less upon the coldness of the winter than 

 upon the coolness of the summer. Not a climate of 

 extremes, but a climate of means, tends to produce 

 glaciation. It appears, accordingly, that the two 

 characteristics of the seasons, in an epoch of high 

 eccentricity would tend in precisely opposite direc- 

 tions, as regards glaciation. In one hemisphere, the 

 length of the winter would tend to glaciation, while 

 the intensity of extremes of temperature would op- 

 pose glaciation. In the other hemisphere, the short- 

 ness of the winter would oppose glaciation, while the 

 approximation to a mean temperature would favor 

 glaciation. The actual tendency to glaciation would 

 be, then, the algebraic sum of two values of opposite 

 signs. In which hemisphere would the tendency to 

 glaciation predominate ? And would the absolute 

 value of the algebraic sum of the two tendencies in 

 either hemisphere be sufficient to have any appreci- 

 able influence ? I simply suggest these questions, 

 making no attempt to answer them. 



1 may remark incidentally that there is something 

 aparently unsound in the argumentation by which 

 the advocates of the eccentricity theory seek to show 

 that the hot perihelion summer would not melt the 

 snow and ice. They virtually deny that the perihe- 

 lion summer would be hot, urging that the tempera- 

 ture could not rise above the freezing-point until the 

 ice was all melted. ■* It may well be conceded that 

 the summer temperature could not rise much above 

 the freezing point in the centre of a polar ice-cap, or 

 at the apex of a snow-capped peak. But at the mar- 

 gin of a snow-field, polar or alpine, the climatic con- 

 ditions would be very different. The ice-fields of a 



J Science, iv. 42f), 18S4. 



2 Darwin, ' Journ. of researches during voyage of H. M. 

 S. Beagle,' p. 224. N. Y., 1875. 



3 Lyell, ' Principles of geology,' vol. i. p"; 242. N. Y., 1872. 

 * Croll, ' Climate and time,' pp. 58-67. New York, 1875. 



glacial period would not be created instantaneously 

 in their maximum extent, but would be the results 

 of a slow accumulation for many centuries. As each 

 hemisphere in turn gradually approached the condi- 

 tion in which the climax of its winter would fall in 

 aphelion, the snow-fields would be at first of very 

 small extent. Outside the boundaries of those 

 snow-fields, the land would be heated to a tempera- 

 ture increasingly hot, as year by year the climax of 

 the summer approached the perihelion ; and that high 

 temperature of the surrounding areas would produce 

 rapid melting at the margins of the snow-fields. 

 Moreover, even at the extreme of glaciation, the area 

 covered by ice would form but a small part of the 

 surface of a hemisphere. Cold aphelion winters 

 must be accompanied by perihelion summers not only 

 potentially but actually hot. 



William North Rice. 



Wesleyan University, Middletown, 

 Conn., Aug. 16. 



The causation of pneumonia. 



In Science for Aug. 13, 1886, p. 133, I notice a 

 paragraph relative to results of observations by Dr. 

 Seibert of seven hundred and sixty-eight cases of 

 pneumonia, wherein it appears that pneumonia pre- 

 vails to its greatest extent " whenever there exists a 

 low or falling temperature, with excessive and in- 

 creasing humidity, and high winds." This reminds 

 m© that readers of Science may be interested to know 

 that facts respecting a very much larger number of 

 cases, and respecting pneumonia in different parts of 

 the United States, in England, and in India, — that 

 is to say, in several climates and under different con- 

 ditions, — confirm to some extent the conclusions 

 reached by Dr. Seibert, as mentioned by Science. 

 Such statistics, presented by abstract at the last 

 meeting of the American climatological association, 

 demonstrate, I think, that the sickness from pneu- 

 monia is absolutely controlled by the temperature of 

 the atmosphere. The higher the temperature, the 

 less the sickness from pneumonia ; and the lower the 

 temperature, the more the sickness from pneumonia. 

 This is equivalent to saying that that part of the 

 conclusion of Dr. Seibert which relates to humidity 

 is an error : because the absolute humidity of the at- 

 mosphere is, speaking roughly, inversely as its tem- 

 perature, and there is most sickness from pneumonia 

 when, or soon after, the air is driest absolutely ; and 

 there is least sickness from pneumonia when, or soon 

 after, the air contains the most vapor of water, that 

 is, when the temperature is highest. The error of 

 many who have written on this subject, and prob- 

 ably the error of Dr. Seibert, consists partly in call- 

 ing the ' per cent of saturation of the air ' (techni- 

 cally known as ' the relative humidity,' the humidity 

 of the atmosphere. But the curve for ' relative 

 humidity ' is not, when inverted, the same as the 

 curve for pneumonia, as you may see by comparing 

 such curves, on the diagrams I published, based 

 upon over twenty-seven thousand weekly reports of 

 sickness in Michigan, by observers in different parts 

 of the state, and upon over one hundred and twenty 

 thousand observations of the psychrometer during 

 the same time, namely, the seven years, 1878-84. 

 Relative humidity seems to have an opposite relation 

 in the warm months to what it has in the cold months. 

 The fact, which I think I have completely demon- 

 strated, is, that pneumonia is quantitatively propor- 

 tional to the* coldness and dryness of the atmosphere ; 



