610 



NATURE 



[April 28, 1892 



ture, as to render the task of deciphering their mutual 

 relationships and determining their exact systematic posi- 

 tions an exceedingly difficult, if not an impossible one. 

 At the same time, however, it does not appear to us that 

 the existence of these puzzling and aberrant types need 

 interfere in the least degree with the commonly-accepted 

 classification of the Ungulates, although there may be 

 legitimate doubt as to the propriety of including the 

 Macrauchenias among the Perissodactyles, instead of 

 retaining them with the Toxodonts as a special group, 

 exhibiting on the one hand many generalized features, 

 coupled with extreme specialization in other respects. 



R. L. 



THE CHANGEFULNESS OF TEMPERATURE 

 AS AN ELEMENT OF CLIMA TE. 



/^NE of the features in which the climates of great 

 ^-^ continents most contrast with those of oceanic 

 islands, and those of higher latitudes with the climates 

 of the tropics, is the greater range through which the 

 temperature varies between night and day, and between 

 winter and summer. Another, perhaps not less im- 

 portant, is the greater changefulness of the temperature 

 from day to day. Both of these are comprised under 

 the general expression variabiiity of temperature^ and 

 they are similar in their effects on Mving organisms, but 

 they depend on very different causes, and in their local 

 association are often manifested in very different 

 degrees ; places with a great annual and diurnal range 

 of temperature, displaying great constancy of climate 

 at any given season of the year, while others, at which 

 the former variations are moderate in amount, are, 

 nevertheless, subject to irregular vicissitudes of consider- 

 able magnitude. The Punjab and Sind may be cited as 

 examples of the former class. Western and Central 

 Europe of the latter. 



Now, although from a sanitary point of view these 

 two kinds of variation are of equal importance, the 

 degrees in which they have respectively engaged the 

 attention of climatologists and others are strikingly 

 different. While the daily and annual range of tempera- 

 ture of all the more important and many minor places 

 that have furnished meteorological registers are now 

 well known, or are easily ascertainable from published 

 records, the first systematic inquiry into the changeful- 

 ness of temperature as an element of climate was that 

 made by Prof. Hann in a memoir published in the 

 Sitzungsberichte of the Vienna Academy of Sciences in 

 1875. In this paper. Dr. Hann tabulated the results of 

 ninety stations, seven of which are situated in the 

 southern hemisphere, and the remainder chiefly in 

 Europe, Siberia, Canada, and the United States. The 

 extraction of the data was not a httle laborious, since it 

 consisted in taking out from the daily registers, of gener- 

 ally from five to ten years, the differences of the mean 

 temperatures of every pair of successive days throughout 

 the whole period ; then classifying them according to 

 algebraic sign, as rises or falls of temperature, and also, 

 in certain cases, according to their incremental values. 

 The means of these different categories were then taken 

 month by month, and the results are given in numerous 

 tables in the memoir. The changefulness of tempera- 

 ture at any given place is the general mean of all 

 changes during the period considered, irrespective of 

 their being rise or fall. As instances of these, I take the 

 following three stations, representing respectively the 

 climates of Siberia, England, and Canada. They show 



I The term " variability " of temperature, adopted by Mr. Scott for the 

 element now in question, has been already used in so many different senses, 

 that in this paper I have adopted in preference the term "changefulness," 

 which is not open to the same objection. 



the average change of any two consecutive days on the 

 Fahrenheit scale. 



NO. I I 74, VOL. 45] 



These three stations serve to illustrate the fact, amply 

 confirmed by the general tables, that temperature is sub- 

 ject to greater and more rapid changes in the winter 

 than in the summer ; either December or January being, 

 as a rule, the month of greatest variability. 



Since the publication of this memoir, the inquiry thus 

 started by Dr. Hann has been followed up by several 

 writers with especial reference to particular countries. 

 Prof. O. Doring, for instance, has thus discussed the 

 statistics of the Argentine Repubhc ; Herr E. Wahlen, 

 those of 18 stations in Russia ; Dr. V. Kremer, those of 

 57 stations in Northern Germany ; and Mr. Robert Scott, 

 those of 7 observatories in the British Isles, at which the 

 temperature has been recorded by thermographs since 

 1869. These are Valentia, Armagh, Glasgow, Aberdeen, 

 Falmouth, Stonyhurst, and Kew. At all these stations 

 the variation was found to be less than at Oxford ; but 

 this maybe partly due to the longer period (15 years) 

 over which the records extend, and partly also to the fact 

 that the daily means compared are those of the twenty- 

 four hourly measurements of the thermograph curve, 

 whereas the Oxford register was for 10 years only, and 

 the observations less numerous. On the general average 

 of the year, it was greatest at Kew (2'7), and least at 

 Falmouth and Valencia (i'^'Q). 



Finally, Dr. Hann has resumed the subject in a 

 memoir published in the Transactions of the Vienna 

 Academy,! in which he discusses the temperature records 

 of 66 stations in the Austrian Empire and the adjacent 

 territories, of which one-half extend over from 10 to 20 

 years, and the majority of the remainder over at least 

 five years ; all, however, are corrected to the period 

 1871-80. In the case of Vienna, not less than 91 years 

 have been included in the reckoning, and this register 

 affords the means of comparing the results of any decade 

 with those of a long period. 



The first point that stands out in the results of this 

 discussion is that even a period of ten years is in- 

 sufficient to give more than an approximate value. The 

 general mean change at Vienna, between any two con- 

 secutive days, is 3°"4 F., but in the decade 1861-70 it 

 was only 3°'26, whereas in the decades 1801-10 and 

 1871-80 it averaged 3°'53. The means of the individual 

 months show much greater variation ; that of December 

 especially, ranging between 3°'2 and 4^*3 in different 

 decennia, or through 30 per cent, of the general mean 

 for the month. It is evident that when computed from 

 shorter periods than ten years the discrepancies will' 



I "Die Veranderlichkeit der Temperatur in Oesterreich," von J. Hann. 

 W.M.K. Akad., aus dem Iviii.Bande der Mai. Naturwiss. Classe der k. 

 Akad. d. Wissenschaften. 



