NA TURE 



565 



THURSDAY, OCTOBER 26, 1876 



WEA THER CHARTS AND STORM WARNINGS 



Weather Charts and Storm Warnings. By Robert H. 

 Scott, M.A., F.R.S,, Director of the Meteorological 

 Office. With numerous Illustrations. (London : 

 Henry S. King and Co., 1876.) 



" \\0 you understand these Isobars on the weather 

 -L/ charts ? " we asked an amateur meteorologist who 

 was showing us the curves which represented his own 

 barometrical observations. " Well, I cannot say I do," 

 he replied ; " they are very interesting and curious, 

 twisting one day one way, next day another way, and the 

 third day turning all round." It is this not uncommon 

 ignorance which the Director of the Meteorological 

 Office seeks to dispel. His object is "to explain to the 

 reader what he can learn from a careful study of the 

 information published in the newspapers or in the daily 

 weather reports," and for this end he has "attempted to 

 give to the public an account of the actual state of our 

 knowledge at present." He then exposes to public gaze 

 all the mysteries of the Weather Office ; he draws aside 

 the curtain, and shows us 



His " copper- plate, with almanacks 

 Engraved upon 't, and other knacks ; 

 His moondial, with Napier's bones, 

 And other constellation stones." 



The following are among the most important of these 

 talismans : — The cyclonic law of the northern hemi- 

 sphere — that if we turn our backs to the wind the higher 

 barometer will be on our right hand, the lower baro- 

 meter on the left ; that the force of the wind is connected 

 with the closeness of the isobars to a considerable ex- 

 tent ; that we never have a storm unless the difference of 

 pressure at two stations in the British Isles is less than 

 half an inch of mercury. That cyclones proceed, in 

 general, eastwards, their approach being frequently 

 heralded by a tendency of the isobars to form closed 

 curves ; and that this is first seen in most instances 

 towards the west coast of Ireland. These conclusions 

 differ little from those which Dr. Lloyd deduced in 

 1854 from his study of atmospheric variations in Ireland. 

 Anti-cyclones which have their greatest pressure at the 

 centre are most frequently connected with light winds 

 and fine weather. 



All the deductions are illustrated by charts and curves 

 from self-registering instruments, which enhance the 

 value of this useful little volume. 



Nothing, however, is more interesting than to see how 

 the theories of meteorological writers for the last half 

 century stand the test when confronted with the daily 

 observation and practical application of facts. We can- 

 not open a work on meteorology without finding all the 

 great phenomena of varying atmospheric pressure as- 

 cribed to the action of the sun's heat in producing vapour 

 and expanding the atmospheric gases. Thus the baro- 

 meter is said to fall in a country because it is warmer 

 there than in neighbouring countries, the more expanded 

 air overflowing (thus causing a wind in the upper regions) 

 towards the colder country, where the barometer rises ; 

 on the other hand, a surface wind is generated from the 

 Vol. XIV.— No. 365 



colder to the hotter region. But the most important of 

 all movements admitted by every one were the polar and 

 equatorial currents. The chief of the Meteorological 

 Office treats the views of the great authorities to whom 

 we have referred, in the following manner : — 



" For many years it has been the fashion to say that 

 all cold winds flowed from the poles to the equator, form- 

 ing the so-called polar currents, and becoming the trade 

 winds when they approached the tropics, while the warm 

 winds flowed from the equator to the pole, forming the 

 equatorial currents or anti-trades " (p. 20). 



It is very like heresy to speak of " the fashion " and 

 the " so-called polar currents," when their existence has 

 been an article of faith accepted everywhere. It is true 

 no one could say he had observed these currents ; and 

 we, who have sought for them in our own latitudes and 

 within the tropics, have insisted that they were neither to 

 be seen nor felt where their effects were supposed to be 

 the greatest. No doubt one of our greatest writers on 

 this subject put the equatorial atmosphere into one cylin- 

 der, surrounded by warm water, and the polar atmosphere 

 into another, with an ice-cold jacket, and showed that if 

 the stopcocks preventing communication at the top and 

 bottom of the two cylinders, that is, the upper and lower 

 passages from the equator to the pole, were opened, the 

 currents referred to could be made visible. This, we 

 think, is an illustration of what Mr. Scott, immediately 

 after the passage quoted above, refers to as " right in 

 principle." The atmosphere has also been supposed to 

 have an upper surface like a lake, down which the ex- 

 panded gases slide. Every condition in nature — density, 

 distance, temperature, viscosity (besides those unknown 

 to us) have been under- estimated, exaggerated, or 

 neglected. 



The author's conclusions, from his long watch of atmo- 

 spheric variations, are somewhat diflferent. He says : — 



" The motions of the atmosphere are found to be 

 mainly regulated by the distribution of barometrical 

 pressure over the globe, the particles moving from the 

 regions where the pressure is high to those where it is 

 low," &c. (p. 21). 



" Wind is always connected with some disturbance of 

 the pressure of the atmosphere, and it will be at once 

 understood that its existence is due to the tendency of an 

 elastic fluid like air to regain the condition of equilibrium 

 from whence it has by any means been disturbed," &c. 

 (p. 27). 



These conclusions are just the reverse of those usually 

 entertained, especially with reference to tropical cyclones 

 where the diminution of central pressure is attributed to 

 the winds, and the movement in which is illustrated by a 

 whirlpool caused by the difference of velocities, or oppo- 

 site directions of motion of contiguous currents of water. 

 In the cyclones of these latitudes we must suppose Mr. 

 Scott to give, as the result of his experience, that the 

 winds follow and do not precede the diminished central 

 pressure. 



In whatever way the subject is considered there will 

 always remain many facts to some of which the author 

 alludes, which cannot easily be explained by the action of 

 cyclonic winds as causes of diminished pressure j and in 

 these cases the question arises, what is the cause of the 

 latter ? This is no mere idle question, it is connected with 

 the whole subject of weather prediction. 



