544 



METEOROLOGY. 



found to accompany the event: 1, Barometric 

 depressions are principally developed over a 

 region where atmospheric gradients are slight, 

 the exceptions to this rule being those systems 

 (secondary or subsidiary, as they are termed) 

 which first appear as loops or bulges in the 

 isobars of a large pre-existing cyclone. 2. 

 They originate either in the rear of a depres- 

 sion, which has already passed away, or in the 

 interspace between two large anti-cyclones, 

 and more especially when the anti-cyclones 

 are so large that this interspace constitutes 

 what is called a "trough" of relatively low 

 pressure. 3. They are preceded and accom- 

 panied by an enormous condensation of vapor 

 into cloud. 4. They do not, at the moment 

 of their birth, appear to affect the upper cur- 

 rents of the atmosphere, but, if growing large, 

 soon afterward do so. In the depressions, the 

 development of which near the British coast 

 and over the southwest of France gave the oc- 

 casion for Mr. Ley's observations, the greater 

 number originated in troughs of relatively low 

 pressure, and their movements might be said 

 to have been unusually erratic. Yet they 

 obeyed the ordinary rule of progression, in so 

 traveling as to have the highest general press- 

 ures on the right of their course. 



At the meeting of the Royal Meteorological 

 Society, November 11, a paper was read by 

 Mr. C. Harding on the storm of Oct. 15 and 

 18, 1886, over the British Islands. "This 

 storm was of exceptional violence in the west- 

 ern, southwestern, and southern parts of the 

 islands, and was felt over the whole kingdom. 

 By the aid of ships' observations it has been 

 tracked for a long distance out in the Atlan- 

 tic. It appears to have been formed about 250 

 miles to the southeast of Newfoundland on the 

 12th, and was experienced by many ocean- 

 steamers on the 13th. When the first indica- 

 tion of approaching bad weather was shown 

 by the barometer and wind at the western out- 

 posts of the islands the storm was about 500 

 miles to the west-southwest of the Irish coast, 

 and was advancing at the rate of nearly 50 

 miles an hour. The center of the disturbance 

 struck the coast of Ireland at about 1 A. M. on 

 the 15th, and by 8 A. M. was central over Ire- 

 land. The storm traversed the Irish Sea, and 

 turned to the southeast over the western mid- 

 lands and the southern counties of England, 

 and its center remained over the British Isles 

 about 34 hours, having traversed about 500 

 miles. It afterward crossed the English Chan- 

 nel into France, and subsequently again took a 

 course to the northeastward, and finally broke 

 up over Holland. In the center of the storm 

 the barometer fell to 28'5 inches, but as far as 

 the action of the barometer was concerned 

 the principal feature of importance was the 

 length of time that the readings remained low. 

 At Greenwich the mercury was below 29 inch- 

 es for 40 hours, and at Geldeston for 50 hours. 

 The highest recorded hourly velocity of the 

 wind was 78 miles from northwest ; but during 



gusts the velocity was probably equal to 120 

 miles an hour for a few moments. The force 

 of the gale was very prolonged. The erratic 

 course of the storm and its slow rate of travel 

 while over the British Islands were attributed 

 to the presence of a barrier of high barometer 

 over northern Europe, and the attraction in a 

 westerly direction that was produced by the 

 great condensation and heavy rain in the rear 

 of the storm. 



Forests. Methodical investigations of the in- 

 fluence of forests on climate have been made 

 in Prussia, France, Switzerland, Italy, and 

 Bavaria. It has been determined, as a general 

 rule, that a forest may modify the normal cli- 

 mate of a country, by depressing the tempera- 

 ture of the air and the ground ; by diminishing 

 the amplitude of variations of temperature; 

 and by augmenting the relative humidity. 

 These causes naturally lead to a diminution of 

 evaporation, but, according to Mr. Woeikof, 

 the Russian meteorologist, the actual diminu- 

 tion is too great to be accounted for by all 

 of them together; and he believes that the 

 predominant factor in the phenomenon is the 

 protection which the forest offers against the 

 wind. 



Observations made at Eberswalde every two 

 hours, from the 15th to the 30th of June, on 

 the daily range of temperature, showed that, 

 at a station outside of the forest, the tempera- 

 ture continued to fall a little after midnight, 

 and then took an ascensional movement, at 

 first rapid, afterward slower, till the maximum, 

 at about two o'clock in the afternoon. It then 

 diminished, rapidly for a while, and then less 

 rapidly, till midnight. The curve of tempera- 

 tures in the forest station followed a similar 

 course, but it reached, at midnight, a higher 

 point in the scale than the curve of the outside 

 station, and then met the latter curve at five 

 o'clock in the morning. The difference in the 

 maxima of the curves was considerably greater 

 than that of the minima, showing that the re- 

 frigerating action of the forest in the daytime 

 was stronger than its ameliorating effect upon 

 the descent of the temperature at night. The 

 maximum in the woods also took place from 

 half an hour to an hour later than in the open 

 plain. 



Numerous comparative observations have 

 shown that the amplitude of the range of the 

 thermometer in the forest, as compared with 

 that outside, is most reduced in the summer. 

 In the summer, also, the influence of foliage 

 woods is more marked than that of pine-for- 

 ests, while in winter the latter exert the greater 

 effect. 



Removal of woods has been shown to make 

 the movement of streams less regular; but, in 

 regard to its effect on the fall of rain or snow, 

 our observations are still too scanty to furnish 

 the data for any rule. Observations made near 

 Nancy indicate an augmentation of rams in 

 wooded districts, which appears to be more 

 marked in winter than in summer, notwith- 



