576 
figured and described, and the methods of observing 
detailed at length ; and emphasis is laid on the necessity 
of securing accurate observations, and of paying atten- 
tion, in making arrangements for observing, to the few 
simple and obvious principles which underlie the science. 
An account is then given of the geographical distribution 
of temperature, pressure, and the other phenomena of 
meteorology, particularly those which are usually com- 
prised under the heads of climate and weather. The 
book is a highly successful one, and evinces a full and 
ready knowledge of the work which has been done by the 
meteorologists of this and other countries down to the 
present time, and we must not omit to add that there is 
an earnest endeavour manifested throughout to give the 
fullest crejit to the first discoverers of the more im- 
portant facts and principles. 
The following extracts, in explanation of hill and 
valley winds and the distribution of rain and weather on 
the two sides of a mountain-chain, show the general 
style of the book : — 
“The day wind brings up moisture to the upper strata 
of the atmosphere, and this is condensed, forming caps 
on the mountain-tops, and often giving rise to thunder- 
storms. The night wind, a descending current, carries 
the moisture with it, and so the highest peaks are oftenest 
clear inthe early morning. The reasons of this rhyth- 
mical change in air-motion are to be sought for in the 
action of heat. In the daytime the air in the valleys and 
on the lower slopes of the mountains becomes heated and 
expanded. The isobaric surfaces over such districts 
rise, and the air so raised has a tendency to flow towards 
the mountains and up the upper valleys as long as the 
heat action over the lowlands is maintained. At night the 
temperature in the valleys falls, and the air lying in them 
contracts, producing a partial vacuum. This causes the 
air above to descend, so that a downward current is 
generated, which lasts all through the night. - . . 
“When wind coming in from the sea, and therefore 
charged with moisture, meets a mountain-chain, it is 
forced to rise; it is cooled by rising, and made to give 
up much of the vapour it brings with it in copious rains. 
The result is that the air is rendered dry and cold. If 
now the average height of the cols of the chain above the 
plain country beyond be 4000 feet, the air in its descent 
may receive an increment of temperature of over 20°, 
and as at the same time its capacity for containing 
moisture will be increased, it will be felt as a dry hot 
wind. This is the explanation of the characteristics of 
the Féhn of Switzerland.”’ 
This gives the true explanation of the increased humid- 
ity observed during the hottest hours of the day on the 
Faulhorn and similar elevated situations. 
A long extract is given (pp. 269-275) from Laughton’s 
“Physical Geography,” summarising the broad features 
of atmospherical circulation as exemplified by the trades 
and anti-trades, in which it is stated that in both hemi- 
spheres to the north or south of the parallel of 30° or 
40° a strong westerly wind blows with great constancy all 
round the world;—and that, alike in the Atlantic and 
Pacific; in North America, west of the Rocky Moun- 
tains; in the Eastern States; in European Russia and 
Germany, and in Northern Asia, there is found the same 
predominance of westerly winds. A more decided ob- 
jection might have been made to the above view than by 
stating that the winds of the temperate zone and of the 
higher latitudes seem to be regulated by the distribution 
of pressure. Laughton’s statement might possibly be 
NATURE 
& 
[ April 19, 1883 
accepted if we had before us little more than Horsburgh 
and the other directories of the navigator. In the north- 
west of Iceland observations show on the mean of the year 
212 days when the wind blows from some easterly point, 
and only 71 days*when it blows from any westerly point, 
and these prevailing winds of Iceland are essentially 
typical of the winds of an extensive region of the north. 
The cyclonic and anticyclonic systems of winds observed 
on the surface of the earth in ‘connection with the well- 
known seasonal areas of low and high pressure are not 
merely surface winds, but extend to a considerable height 
in the atmosphere. This is evident from the considera- 
tion that in winter, pressure is 1°115 inch higher in Siberia 
than in Iceland, and in summer o’860 inch higher in the 
Atlantic than in the south-west of the Punjaub in the same 
latitudes, and that great disturbances of the equilibrium 
of the atmosphere must necessarily obtain to very great 
heights. It therefore follows that over large portions of 
the northern hemisphere gradients for prevailing westerly 
winds cannot be formed within many thousand feet of the 
earth’s surface. 
Mohn’s happy classification of thunderstorms into heat 
thunderstorms and cyclonic thunderstorms is adopted and 
illustrated. The former is the type which predominates 
in summer and in hot climates, while the latter are cha- 
racteristic of our Atlantic coasts, Iceland, and Norway, 
and are a not infrequent accompaniment of cyclonic dis- 
turbances. Cyclonic thunderstorms have their maximum 
period in winter, and though they occur at all hours of 
the day, yet long-continued observations show a distinct 
diurnal period having the maximum during the night ; 
and in some regions so strongly marked is this phase that, 
of the twenty-three cyclonic thunderstorms which occurred 
in Iceland in fourteen years, only three took place at an 
hour of the day when the sun was above the horizon. On 
the other hand, heat thunderstorms are most frequent 
during the hottest period of the day, or during the early 
afternoon. 
Sheet lightning and the so-called summer or heat 
lightning are stated to be nothing else than the reflection 
of, or the illumination produced by, distant electrical dis- 
charges. This opinion, so long and generally entertained, 
is not supported by observation. At Oxford, during the 
twenty-four years ending 1876, the following are the 
number of times which thunder, with or without lightning, 
and lightning unaccompanied with thunder, have been 
recorded during May, June, July, and August, from 3 p.m. 
to 4 a.m. :— 
Thunder. Lightning. Thunder. Lightning. 
3-4 p.m. Ly, Aon 10 [O=1i panes 02) ees 
4-5 4 27 I PUSINOE, vga tt! 30 
5-6 ,, 29 Oo ...mid.-Iam.... 7 27 
67 "5; 21 fe} 12) Posi) sone 27 
728m Gp noes OE 2 223) (55) fl 120 no 
$-0: Son) eee I =A 143 nS 
g-I0 ,, 7 7 
Thus at Oxford the hours of maximum occurrence of 
thunder is from 4 to 6 of the afternoon; but the hour of 
maximum occurrence of sheet lightning or heat lightning 
is delayed tillabout midnight. These different times, but 
above all the larger number of cases of heat lightning 
over thunder about midnight, which are nearly as 7 to 2, 
proves that a large proportion of these cases of heat 
lightning at Oxford were not the reflection of distant 
— 
