: 
APRIL 11, 1912| 
NATURE 
151 
HEAT-WAVES IN ASIA: SUNSHINE AT 
TRIESTE. 
R. H. VON FICKER contributes to the Sitzungs- 
berichte d. K. Akad. der Wiss., of Vienna 
(vol. cxx., part vi., June, 1911), a comprehensive dis- 
cussion of “heat-waves”’ travelling across northern 
Europe and Asia during the years 1898-1902. He 
deals with eleven cases in which the mean daily tem- 
perature increased by at least 10° C. in twenty-four 
hours, and the course of the change could be traced 
over a large area. The majority of the ‘‘heat-waves”’ 
occurred in winter, and three of these and the single 
summer-'‘ wave” are discussed in detail. The mean 
values for the eleven cases are treated very fully, the 
synchronous conditions of wind, pressure, change of 
pressure, humidity, and cloud each receiving as full 
a consideration as the available data permitted. 
In a previous investigation of cold waves in the 
same region, Dr. Ficker found that the wind in the 
cold area was roughly perpendicular to the wave-front, 
indicating that the change of temperature was pro- 
duced by the horizontal transference of a mass of 
cold air. The result may be compared with the deduc- 
tions of Lempfert and Corless from a detailed investi- 
gation of line squalls in this country. With heat- 
waves, however, the wave-front travels towards the 
east or south-east, while the wind is from south-west. 
The author concludes that there is a continuous south- 
west current which is lifted temporarily by the mass 
of cold air in the cold waves, and that in the general 
circulation of the atmosphere this warm south-west 
current is the medium through which air is carried 
polewards. He does not attempt to determine the 
motive nower which pushes the cold air equatorwards. 
It may be the unexpended momentum of a south-west 
current which has crossed the polar regions, or it 
may be due to the effect of the earth’s rotation on the 
south-west current in the rear of the cold wave. 
In the northward progress of the warm current, the 
cooling is less than the warming which the cold wave 
experiences as it moves towards the equator, and this 
is attributed to the lifting of the warm current, which 
is thereby removed from the cooling effect of the earth. 
The latent heat of the vapour carried by the current 
ought also to be an important factor. 
The maximum temperatures at different places in 
the ‘“‘heat-wave”’ differ much less from one another 
than in the cold wave, and the increase of tempera- 
ture is greatest in the coldest places. There are 
exceptional cases in Central Asia which are explained 
by the dynamic warming of descending air (Fohn). 
The velocity of the wave-front is about 33 km. per 
hour, which agrees fairly well with the corresponding 
velocity found for cold waves. The latter would 
naturally expand laterally as they progressed, so that 
the actual velocity of the wave-front ought to be less 
in the case of heat-waves, for which no such lateral 
expansion is possible. 
The relative humidity frequently increases with the 
advent of the ‘‘heat-wave,”’ and the absolute humidity 
invariably does so. The amount of cloud also in- 
creases in general. The conclusion is drawn that 
the ‘‘heat-wave”’ cannot be attributed to descending 
air, but must be due to the horizontal flow of warmer 
and more humid air. It is difficult to reconcile this 
with the conclusions based upon the observations of 
wind, and it is possible that the surface wind does 
not provide a satisfactory basis for the theory developed 
by Dr. Ficker. It is now established that the upper 
wind, at moderate altitudes, deviates considerably from 
the wind at the surface, and has approximately the 
same direction as the surface isobars. Above the 
south-west winds found by Dr. Ficker, there would 
probably be a general current from west to east, or 
NOw@225, VOL. 89] 
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approximately in the direction of motion of the wave- 
front, and the general progress of the wave may be 
governed by this upper current. 
The paper will contribute to the solution of the 
problem of scientific forecasting in its wider aspects, 
and the author is to be congratulated on the excellent 
use which he has made of the data contained in the 
publications of the Russian Central Observatory. 
The same number contains a discussion by Dr. 
E. A. Kielhauser of nineteen years’ records of the 
duration of sunshine at Trieste. 
In the daily variation the maximum occurs at 1 p.m. 
in winter and at 2 p.m. in the other three seasons, 
but in summer there is a secondary maximum at 
Ii a.m. with nearly the same value as the principal 
maximum. At Kew the principal maximum in 
summer occurs at or before 11 a.m., and is consider- 
ably in excess of the secondary afternoon maximum. 
The most interesting table is one giving the number 
of occasions in each month on which series of 1, 2, 3 
. consecutive days without sunshine occurred. 
October had the greatest number of single days, and 
December of series of 2, 3, 4 days, but January had 
the greatest total number, and stands out as the month 
in which the longest sunless periods occur. No period, 
however, exceeded eleven days, so that Trieste is more 
favourably treated than London in this respect. At 
Westminster in January of the present year there were 
thirteen consecutive sunless days, at Kew fourteen. 
The difference in favour of Trieste is not sufficient, 
however, to justify its inclusion in the ‘sunny south.” 
In winter the chances are in favour of a sunless day 
being followed by a second sunless day, but the case 
is reversed in summer, and on no occasion did two 
consecutive sunless days occur in August, which had 
only ten such days in the nineteen years. July is the 
month with the greatest total duration, but August 
had the smallest number of sunless days. 
E. Go.p. 
THE TOTAL ECLIPSE OF THE SUN, 
APRIL, 1911, AS OBSERVED AT VAVAU, 
TONGA ISLANDS." 
Ors to very unfavourable weather, the eclipse 
of last year was observed in the presence of a 
large amount of cloud. The lecturer, while only 
being able to refer to the few results that were 
secured, took the opportunity of explaining why ex- 
peditions were sent out to observe eclipses, and how 
a large expedition is organised when it is known that 
the assistance of one of his Majesty’s ships is avail- 
able. Introducing the subject with a few words as 
to the conditions which cause total solar eclipses, 
their occurrence in families, &c., he then pointed out 
that the sum total of time spent in useful observation 
at all the eclipses which have been observed up to 
date is very short, and amounts probably to less than 
three hours, for an eclipse cannot last longer than 
eight minutes, and does not, as a rule, exceed three 
minutes. 
The line of totality of last year’s eclipse extended 
across the Pacific Ocean, commencing at New South 
Wales, Australia, and terminating in the ocean just 
to the west of Central America. The central portion 
of the track passed near the islands of Tofua, Vavau, 
Tau, Nassau, and Danger Islands. Tofua being an 
active volcano, and Tau, Nassau, and Danger Islands 
difficult of access, most of the expeditions located 
themselves on Vavau, where there was a very safe 
anchorage for ships and where stores were obtainable. 
All the parties settled close to Neiafu, the chief village 
1 Abstract of a discourse delivered at the Royal Institution on Friday 
March 1, by Dr. William J. S. Lockyer. 
