August 23, 1883] 



NATURE 



399 



j 11 1 Max. 

 Inch. Time. 



+ OIO ... II p.m. 



+ 'OU ... IO ,, 



+ '014 ... IO ,, 



+ -OIO ... 9.30 „ 



+ •002 ... II ,, 



surfaces of the globe from the time of the morning maxi- 

 mum to the afternoon minimum. 



The following are the four phases of the diurnal varia- 

 tion of the pressure in summer at a few of the more 

 strictly insular stations : — 



1st Min. 1st Max. 



Inch. Time. Inch. lime. 



Amsterdam ... -'013 ... 4.30 a.m. ... +007 ... 11.30 a.m. 



Falmouth ... -'019 ... 4 ,, ... +-009 ... 0.30 p.m. 



Valeutia ... - 'OiS ... 4 ,, ... + - ooo ... 0.30 ,, 



Helder - 01S ... 4 „ ... + - ooS ... 1.30 ,, 



Sitka - T>o6 ... 6 „ ... + 006 ... 2.30 ,, 



2nd Min. 

 Inch. 1 ime. 



Anwerdam ... -'004 ... 530 p. m 



Falmouth . . . - - oo 1 . . . „ 



Valentia ... - 'ooo ... 5 ,, 



Helder ... ... + -ooi ... 6 „ 



Sitka + 'coo ... 7.30 „ 



The chief points to be noted here are the large amounts 

 of the 1st min , and the small amounts and retardation in 

 the times of occurrence of the 1st max. and 2nd min. All 

 these peculiarities are presented in a still stronger form 

 by the results of June taken by itself. Thus at Sitka the 

 times of the four phases are 7 a.m., 3 p.m., 7.30 p m., and 

 1 1 p.m., and the 2nd min. and 2nd max. become very 

 small. It is only, however, over the open sea in the 

 higher latitudes where the 2nd min. and 2nd max. dis- 

 appear, resulting in one minimum in the early morning 

 and one maximum in the early afternoon. This afternoon 

 maximum therefore really represents the a.m. max. of the 

 lower latitudes of the ocean and of land surfaces — which 

 phase of the pressure occurs at different hours from 

 7 a.m. to 3 p.m. according to latitude and geographical 

 position — and hence subsequent to the a.m. or 1st max. 

 the lines representing the diurnal barometric variation 

 are everywhere to be represented by minus signs. 



The highly important result remains that over the 

 open sea in the higher latitudes of the Atlantic and the 

 Southern Ocean the diurnal curve of pressure, as shown 

 by the observations of the Norwegian and Challenger 

 Expeditions, exhibit only one minimum and one max- 

 imum and that the curve generally resembles the curve of 

 temperature. Hann's remark that "in the daytime the 

 air in the upper strata above the land flows towards the 

 sea, occasioning an increase of pressure, which even on 

 the coast asserts itself by retarding the morning maxi- 

 mum and the afternoon minimum ; in the evening and at 

 night this process is reversed, a current of air in 1 he- 

 higher strata llo as from the sea to the land; hence the 

 pressure increases, diminishing on the coast, and the 

 evening maximum becomes inconsiderable," simply ac- 

 counts for part of the phenomena as observed near the 

 coast and at no great distance out a. sea. It leaves, 

 however, the outstanding feature of the diurnal atmo- 

 spheric pressure over the open seas of high latitude^ 

 untouched and unexplained. To this point we shall 

 return on an earl) occasion. 



The curves of the diurnal distribution of the pressure 

 of the aqueous vapour of the air are very interesting. 

 Grouping the three series together and bloxaming the 

 results, we obtain a curve of great simplicity, showing 

 one maximum and one minimum, the maximum rising 

 01 mm. above the daily mean from 11 a.m. to 3 p.m., 

 and the minimum falling 01 mm. below it from 10 p.m. 

 to 4 a.m. In other words, the curve of the force of 

 vapour substantially agrees with the curve of tempera- 

 ture, and it agrees with the same curve obtained from the 

 open sea observations of the Challenger. The curve for 

 the Challenger observations taken near land shows a dip 

 from about 11 a.m. to 3 p.m. which is quite decided, 

 though not of to pronounced a character as is seen over 

 land during the summer months. A slight dip occurs in 

 the separate curves of the Norwegian Expeditions for 

 1876 and 1877, svhich doubtless is due to the comparative 



proximity to land where several of the observations were 

 made. This reduction in the amount of the aqueous 

 vapour which is observed to occur during the hottest 

 hours of the day is due to the descent of the drier air 

 of the upper regions to take the place of the air which 

 ascends from the heated surfaces of the earth. This 

 diminution of the aqueous vapour of the air is not 

 restricted to the air over the heated surfaces, but, as 

 shown by the Challenger and Norwegian observations, 

 it extends for some distance out at sea, probably as far as 

 the indraught of air from the sea towards the land heated 

 by the noonday sun is felt. 



The curve of the diurnal velocity of the wind deduced 

 from the whole of the observations and bloxamed reveals 

 the fact that the influence of the lower pressure which 

 obtains over the interior of Scandinavia, as compared 

 with that round its coasts during the hottest months ot 

 the year and the hottest hours of the day, extends much 

 further out at sea than might have been supposed, and the 

 curve of the force of the aqueous vapour just referred to 

 corroborates this view. The curve of the diurnal velocity 

 of the wind substantially agrees with that of the tem- 

 perature. 



The same overpowering influence of the sun is equally 

 seen in the diurnal distribution of the tempeiature of the 

 surface of the sea, the curve for which agrees with that 

 for the temperature of the air. The curves for the sepa- 

 rate years show, however, such striking differences in the 

 mean amounts of the diurnal variation, and particularly 

 in the hours of occurrence of the maximum excesses above 

 the day means, as to show that a less close approximation 

 to the true diurnal curve has been arrived at for the tem- 

 perature of the sea than for any of the other meteoro- 

 logical elements. In carrying out this work and discuss- 

 ing the results, Prof. Mohn has clearly made a contribution 

 of the greatest importance to the physical geography of 

 the sea. Alexander Buchan 



VIENNA 



INTEKNA TION. IL ELECTRICAL 

 EXHIBITION 



THE Vienna Electrical Exhibition was opened to-day 

 to the public. The patron of the Exhibition, the 

 Crown Prince Rudolph, the Portuguese Crown Prince, 

 the Princes of the Imperial family, the higher function- 

 aries of the State, and the Foreign Co nmissioners were 

 present at the opening ceremony. The attendance of 

 the public was small ; only 4000 persons have visited 

 the Exhibition to-day, the weather being rainy. The 

 Crown Prince, in replying to the address delivered 

 by Baron Erlanger, the president of the Exhibition 

 Commission, said that it did not seem to be only 

 by chance that the third and greatest Electrical Ex- 

 hibition is held in Vienna — in the town in which, in 

 1833, lucifer matches were invented by Preschel, from 

 which, in 1837, the stearine candle found its way through 

 the whole world, and where the lighting of streets by gas 

 had been suggested by the Moravian, Zinser, before it was 

 carried out in England. 



The Exhibition, though still incomplete, promises a 

 good display illustrative of the great progress made 

 in practical electricity during recent years, and showing 

 how the application of electricity for the various purposes 

 of industry and of daily life is becoming more and more 

 common. So far as we can see now, although the work 

 of installation of the machinery and apparatus is not yet 

 completed, the Exhibition will stand comparison with 

 previous exhibitions as to the number and variety of 

 exhibits and the arrangement of the whole. From the 

 official catalogue published to-day we learn that there are 

 579 exhibitors, 223 of whom are from Austria, 133 from 

 France, 68 from Germany, 27 from Russia, 16 from Italy, 

 10 from Denmark, 13 from America, and 27 from Eng- 

 land. Thus the Exhibition is rather a Continental one, 



