574 MONTHLY WEATHER REVIEW. AUQUST, 1919
the thermograph in the early hours; but this was not serious because the temperature at that time was, for the purpose, not used, and t,he consequent ‘(cusp” in the curve afforded a record of the clearness of the sun- riss. The temperatures as observed a t Mandeville are quite interesting. The highcst temperature recorded durin four years 1912-1916 was 59.2” F. The lowest recorde temperature was 56.1” F. On four days only did the thermometer fail to reach 70” F. The warmest ni ht,
74.6” F. The mean daily variation from the normal for four years is 12.4’.
When the thcrnionieter goes above S 5 O it is considered hot., and whrn i t drops below 60” i t is considered cold. IVind-Wincl observations were not macle auto- matically as no anemometer or wind recorclin a paratus was carried. Cihcral obsprvations showecf [owever, that the prevailing wind comes from the ESE. While hurricanes occasionally pass near the station, the most severe was t,ho one of November, 1912, when the masi- mum wind velocity was estimated a t 55 miles per hour. It was believed that owing to the broken and hilly naturc of the country about Mandeville, this figure is probably correct. The mean of 28
years is S7.M inches. The minima of the rainfall seem t.0 occur in February and July. It always rains harcl, and most generally comes in sharp, short showers. So
sharp is the edge of a shower that it has rained on one side of the house and not at all on the other. 011 the average it rains 182 days each year. The heaviest rain- fall recorded for 34 hours was 9.90 inches. Attention is called to the fact that the rainfall minima for the island seem to have a certain relation to the sunspot period. It was concluded that there was a diminishing of rainfall about 1.3 years after every sunspot masinium and minimum, although no attempt is made to trace the relation definitely. Ds~c.-Dew is quite important in astrononiical work and i t was found to be so heavy that a desirable means of nieasuring it was sought. It was memured by tlie fol- lowing device, consisting “ of a square blackened funnel nieasurin 60 cni. on a side and 10 cm. in depth. It is
the ground, and is so arranged that fresh air can reach the under side of the funnel, which is also blackened. A bottle collects the precipitated moisture. While some of this is retained on the funnel, ex eriment shows that
precipitated on the under side of it.” The maximum dewfall recorded was one standard gallon per hundred square feet of surf ace. 074?amess.-The clearness of the sky and the quality of the ‘(seeing” are, of course, of paramount importance to the astronomer. observations were made on sun- shine and starli ht as well as u on the clearness of the
days and nights is unusually large. Also the sky seemed much clearer than in temperate zones. “The sky appears darker, possibly owing to the complete absence of any more or less permanent auroral illumi- nation. The most noticeable effecta are in the whiteness of the Moon as distinguished from its yellow color in the north, the brilliancy of the Milky Way, the distinctness of the Zodiacal Band a t midnight and of the Ge enschein, and the brilliancy of comets’ t,ails.” In general, it is believed that good ((seeing” does not associate itself with dry air,
%
August 13, 1915, tlie thermometer did not fall be f ow
RuinfnW.-Rainfall is very heavy.
supportec 7 in a wooden box a t a height of 50 cni. above
this is in a large part compensatec P by some which is
at,mosphere, an fi i t was found t K a t the number of clear
which sometimes appears as early as 9 o’cock, f
but tho very contrary, for the best “seeing” a t Mande- ville seemed to conie on very wet nights. This tends to disprove the contention that observatories should be built in deserts. The only advantape of such a location over that in Jamaica is that there might he a gmater per- centage of clear nights, a.lthough that is not necessarily true.-C. L. ill.
THE RELATION BETWEEN WIND AND THE DISTRIBUTION OF PRESSURE.’
By H. JEFFREYM.
[Abstract reprinted horn Nnture (Lonhn), July 17, 1919, p. 395.1
A classification of some 600 wind observations over the North Sea, according to their velocities and directions, showed that the most striking feature of the resulting values was their asymmetrical fre uency distribution.
class, it was inferred that it could be produced only- by variation in turbulence or systematic contortion of the isobars, on a scale too small to be recorded on the weather map. The latter cause, however, and also such variations in turbulence as keep the coefficient of eddy viscosity the smie at all hcigllts, would lead to strong coldations between S/G and a, which are not observed. Hence it, is concluded that the principal cmse of variation in the relation of the surfscc: wind to the gradient is varia- tion in the vertical distribution of turbulsnoe; and it is shown that such variation could give the effects actually observed.
From the fact that this wits noticea % le in nearly every
MOTION OF THE AIR IN LOWES’T LAYERS OF TiIE ATMOS- PHERE.z
Ily G . HELLMAM.
[Abstract reprinte.1 Irom Beicnce .\b:;tmcts, J u !~, 101% 1’. 311.1
The ground wind is investigated by nieasurements of wind velocity at five different liei hts between 5 and
is found that in t,his lowest laver the moan wind Telocities are roportiond to the fourth roots of the corresponding
#he previous work of the author for lieiglits varying from 200 cm. C? m.) to 25s m. above the ground galre rise to a similar result., in which, howerer, the velocities were proportional to the fifth roots of the corresponding heights.-R. C?
200 cm. above unohstructed groun f near Berlin, and it
hei .p its.
LOCAL WIND VARIATIONS.
[Reprinted from Xlctr~rologind Offire rirculor, Mor. 215, 1914, pp. 2-3.1
There is a natural tendency to assume that a single anemometer gives a fair representation of the wind over a large area. A study of the records from the two anemometric stations at Southport shows that the assumption is by no means always justified. At Hesketh Park, the c.limatologica1 station to which all Southport observations, except those of wind, refer, the anemometer vane is 50 feet above ground, 30 feet above the tallest trees in the park, and 30 feet above those nearest it. The records of wind strength, given by an anemobiagraph, and of direction, given by a Basendell anenioscope, show considerable us tiness under all con- ditions. At the Marshside win d stmation, about a mile
1 Royal Societv London June %i 1919.
9 Preuss. Akn3.’Wiss. €thin, d. E. pp. 404-416, 1919. ‘GI. Prof. nota No. 6, p. 5i2, above.