IN EUROPE DURING OCTOBER, NOVEMBER, AND DECEMBER 1863. 193 



barometric pressure, or parts of a degree of temperature, the tables and maps 

 may be accepted as representing the pressure and temperature of the air over 

 Europe, with scarcely any deviation from the truth 



The barometric observations (Table I.) were brought to English inches, and then 

 reduced to 32° and sea-level. Each observation, so reduced, was entered in its 

 place on the map, and lines were then drawn through all those places where the 

 pressure was equal. These isobarometric lines are given for every two-tenths in 

 the difference of the pressure,— for 30-5, 303, 301, 299, &c, inches. 



The lines of temperature have been laid down on a different principle. For 

 lines exhibiting the actual temperature would fail to show, in a sufficiently clear 

 manner, the real bearing of this important element, since the isothermals of 

 October, November, and December run in a very irregular manner over the con- 

 tinent of Europe. Hence not the actual temperature, but the difference between 

 the actual temperature and the mean temperature of each day at the several 

 stations is traced on the maps. 



Dr Buys Ballot has calculated the mean temperature of many places in 

 Europe for every alternate day of the year, and for a few other places ten-day 

 means. The results were published in 1861, in " La Marche Annuelle du Ther- 

 mometr e et du Barometre en Neerlande et en Divers Lieux de V Europe." In the 

 observations of temperature in the " Jaarboek," 1863, not the actual temperature, 

 but the deviations from the mean temperature of each day, are alone given. These 

 I have adopted simpliciter. Of the other stations, I have calculated the mean tem- 

 perature of each day, using for this purpose Dr Ballot's tables, Professor Dove's 

 mean temperatures, as given in " Darstellung der Wdrmeersclieinungen durch 

 Funjtdgige MitteV 1863; the same author's " Monats-und-Jahresisothermen" 

 1864 ; and the data in the Scottish Meteorological Society's " Proceedings" bear- 

 ing on the subject. The differences between these daily means and the daily 

 observed temperatures are entered in Table III., in which the minus sign shows 

 that the temperature was under the mean ; and if no sign is used it was above 

 the mean. The stations are pretty well distributed over Europe, and are suffi- 

 ciently numerous to show the changes of temperature which occurred near the 

 earth's surface before, during, and after the successive storms. They were entered 

 on the maps, and then, as in the case of the barometer, lines were drawn through 

 those places where the differences were equal. They show where the tempera- 

 ture was the average 0°, and then in succession where it was 4°, 8°, 12°, &c, 

 above the average or below it. 



The temperatures as actually observed are given in Table II. 

 The state of the sky with respect to rain, cloud, and fog is indicated in Table 

 II. by means of letters — R showing that it was raining at the time of observa- 

 tion ; C, that at least three-fourths of the sky was covered with clouds ; B, that 

 the sky was either quite clear, or not so much as three-fourths covered ; and F, 



