May I J, 1877] 



NA TURE 



51 



burgh to point out why the barometer does not always indicate 

 real vertical pressure. He points out that as the upper currents 

 of tlie atmosphere when in motion are more mobile than llie 

 lower, and less retarded by friction than the lowest, there are 

 frequent movements or "liftings" from the lower to the upper 

 layers, and this affects the barometric column, " the normal up- 

 ward diminution of pressure which takes place when the atmo- 

 sphere is at rest being greatly altered when its upper portion is 

 in rapid motion." Mr. Tennent says " the practical conclusion 

 from this is obvious. On weather charts the constant rise and 

 fall of the barometer which is there reported, is to a large extent 

 simply due to the passage of air over a resisting surface ; over a 

 surface devoid of friction these mechanical effects would be en- 

 tirely removed, its rise and fall would be greatly reduced, and 

 might be considered as being solely dependent on the effects of 

 heat and vapour. The gradients and isobars which are depen- 

 dent upon it would also be similarly affected. The barometer 

 does not indicate the real weight of the atmosphere, it only ex- 

 hibits the amount of its elasticity from which its real weight can 

 only be deduced when the dynamical element of motion does 

 not enter into one of its currents." . . . "As a general rule, in the 

 British Isles equatorial winds are accompanied by these rapid 

 upper movements, while Polar winds move with a greater uni- 

 formity in the velocity of their various layers, and sometimes 

 even those on the surface move more rapidly when copiously 

 supplied from a vertical source. Tliere is hence a remarkable 

 difference in their mode of inflinv. Equatorial winds as they in- 

 crease in force are hence accompanied by ' lifting ' and a fall of 

 the barometer. Polar winds are not attended by ' lifting,' and 

 if their supply is copious and partly from a vertical source, their 

 increase in force is accompanied by a rise of the barometer. 

 The range of the thermometer is equally great both above and 

 beiow its mean. But with the barometer the extent of its range 

 above the mean is not more than one-half of tliat which takes 

 place when it is below it. When it is below the mean^ equa- 

 torial winds generally prevail which are accompanied by ' lifting ' 

 and extensive range. Above the mean. Polar winds prevail 

 which are ,not attended by ' lifting ' or such extensive fluctua- 

 tions. Hence, as a general rule, equatorial winds exhibit ficti- 

 tious or dynamical pressure, while Polar winds possess more 

 nearly real or statical pressure, jbeing .unaccompanied by the 

 mechanical oscillations due to tlie passage of air over a resisting 

 surface." 



Thunderstorms at Antibes on March 26, 1S77. — Col. 

 Gazan has given a brief account, in the Butlttin Interna'.ioiial 

 for April 18, of three thunderstorms which occurred at Antibes, 

 in the south-east of France, on March 26, possessing certain 

 characteristics well deserving of attention. About 7 A.M. a flash 

 of lightning occurred followed by a clap of thunder, and at 7.10 

 A.M. a fall of hail without rain, lasting ten minutes. The hail- 

 stones were for the most part regularly round, quite opaque, and 

 not bigger than comnron peas, the largest nut much exceeding 

 half an inch in diameter. Clear patches of blue sky in the east 

 and south-west formed a striking contrast to a nimbus cloud in 

 the west, which was connected with the upper clouds. Tlie 

 clouds were absolutely motionless, the air so calm that not a leaf 

 was stirring, and the fall of hail exactly perpendicular. At 

 II. 10 A.M. the sky was [entirely overcast, and under the same 

 conditions as before a fresh fall of hail took place, mingled with 

 heavy rain, the hailstones being more equal in size and generally 

 smaller. About 2.30 p.m. a pretty smart shower of rain fell, 

 which, immediately after a flash of lightning followed by thunder, 

 increased in violence, and was accompanied with hail. The 

 largest of the hailstones did not much exceed the largest of those 

 of the two falls preceding. During the whole time there was 

 not a breath of wind until just before the end of the last thunder- 

 storm, when a light westerly breeze sprang up. Col. Gazan 



infers from the quiescent state of the air, as shown by the absence 

 of motion in the clouds, the perfect calm at the earth's surface, 

 and the regular distribution of the hailstones over the ground, 

 that the three thunderstorms were formed immediately over the 

 place and that the phenomena were unattended with any gyratory 

 movement whatever — conclusions which, if correct, have im. 

 portant bearings on the theory of thunderstorms, and therefore 

 are well deserving [Of the most careful examination on the part 

 of observers of the phenomena of atmospheric electricity. 



Meteorology in Italy. — The Rivisia Scientifico IndustriaU 

 publishes a "project for the^constitution of an ItaUan Meteoro- 

 logical Society " from the pen of Prof. D. Ragona, director of 

 the Modena Observatory, in which the writer points out the im- 

 portance of meteorology, and'adds that this science owes much 

 to Italy, as it was in that country that the most valuable meteoro- 

 logical instruments, viz., tlie barometer, thermometer, and rain- 

 gauge, were invented. More than 100 meteorological stations 

 are already in existence, some of which are renowned for exact- 

 ness of the determinations and delicacy of the researches they 

 Iiave made. They have also the advantage of great variety in 

 their elevations, more than sixty of them being situated between 

 200 and 2,500 metres above sea level. Several Influential 

 persons have already consented to become members'' of the new 

 society, and amongst them are the Minister for Agriculture, 

 Industry, and Commerce, and Prof. G. V. SchiapareUi, of 

 Milan. We wish the project every success. 



Meteorology in France. — The prefects of three different 

 departments have published a circular notifying to the mayors of 

 the several communes under their authority the required condi- 

 tions for receiving daily the weather-warnings issued by the ob. 

 servatory. It is the first time that official action has been taken 

 for the propagation of the system inaugurated by M. Leverrier, 

 The progress made under his direction is very remarkable, and 

 meteorology is becoming very popular in every part of France. 

 The system is to continue on the voluntary principle. 



Sunday Weather Warnings. — The weather telegrams 

 sent every Sunday by the British Meteorological Board have 

 been discontinued, as it is only during winter that the taking of 

 observations has been authorised. The head of the Meteoro- 

 logical Office has written to M. Leverrier notifying the fact, and 

 expressing a hope that the Sunday service will be resumed 

 next September. This decision has given rise to some sarcastic 

 paragraphs in the French leading journals, which doubt whether 

 storms will be found strict Sabbatarians even in summer. 



GEOLOGICAL NOTES 

 Geological Map of Belgium. — Considerable discussion 

 has lately taken place in Belgium regarding a detailed geological 

 map of that kingdom which it has been proposed to construct. 

 The Academy of Sciences, the Geological Society of Belgium, 

 and the Association of Engineers have all formed committees 

 of inquiry as to the best methods of preparing the map. It 

 may interest geological readers to know the scheme which after 

 prolonged discussion^has been agreed upon liy the Geological 

 Society of Belgium. The organisation of the staff is proposed 

 to include a geological committee charged with the actual sur- 

 vey, and consisting wholly of geologists ; a cartographical com- 

 mittee composed of cartographers and geodesist-, to take charge 

 cf the engraving and publication of the map in chromolitho- 

 graphy ; a director, as president of both committees, to be 

 appointed by the King, on the recommendation of the geological 

 committee. Each committee is to be independent of the other, 

 and to have the utmost liberty within its own proper sphere of 

 action. The Government, on the recommendation of the Royal 

 Academy ot Belgium, names the first five members of the geo- 



