A 
y 
March 15, 1883 | 
tion, as well as the purity of the air at great heights, especially 
above the snow-line. 
Prof, Tyndall has certainly lost sight of this when he attri- 
butes the diathermacy of the air in winter only to the small 
amount of vapour of water. The same is the case when he 
points to the relatively small nocturnal radiation on clear nights 
in many tropical countries. In the case of many of them, 
besides dust and smoke, the igh relative humidity has much to 
do with the small amount of cooling during the night. What 
quantities of latent heat are liberated by the formation of dew 
in humid climates of low latitudes, and how much the nocturnal 
cooling must be impeded by it, everybody can imagine who has 
been in these countries, or only read scientific travels to them. 
A. WOEIKOF 
Diurnal Variation in the Velocity of the Wind 
THE observations discussed in Mr, Buchan’s interesting article 
on this subject leave little to be desired, and with most of the 
conclusions meteorologists in general will agree. I am surprised, 
however, to find such an eminent authority accounting for the 
large diurnal oscillation on land, solely on the ground of its being 
due ‘‘to the superheating of the surface of the ground, and to the 
ascensional movement of the air consequent thereon, which tend 
to reduce the effects of friction and viscosity of the air.” 
There may perhaps be more hidden within this sentence than 
appears from the wording of it; but, taking it as it stands, it 
certainly omits what I believe to be the most important factor in 
the whole result, viz., the interchange of motion between the upper 
and lower layers of the atmosphere, occastoned by the ascensional 
movements during the day over superheated land. This has 
been most clearly shown by Dr. Képpen in an article in the 
Austrian Zeitschrift fiir Meteorologie,’ by successive rejection of 
inefficient causes, to be the only means by which such increase of 
velocity could be occasioned near the earth’s surface. 
It is not clear, moreover, how the ascension currents could other- 
wise diminish the friction of the air enough to account for such a 
large diurnal increase of velocity. The effect of the increased 
temperature alone, would certainly be to increase the friction, 
but as K6ppen shows from Meyer’s formula for the coefficient 
of gaseous friction, the daily range of temperature would only 
cause the friction of the air to vary from } to 1 per cent. of its 
whole amount,” so that this factor is evidently without any 
appreciable influence on the diurnal period. 
In the paper already referred to, Dr. Kippen has gone into 
the whole question most minutely, and a perusal of it will, I 
think, convince most persons, that the chief factor in causing the 
diurnal increase of wind-velocity over land is the intermixture 
of air (/uft-austausch) resulting from the uprise of heated air 
from the surface, and the consequent downfall of cooled air to 
it, ‘‘ bringing down with it,” as Espy told the British Associa- 
tion in 1840, ‘“‘the motion which it has above, and which is 
known to be greater than that which the air has in contact with 
the asperities of the earth’s surface.” 
Among the facts cited by Koppen in favour of his theory may 
be noted the following :— 
1. The fact that in Europe the ratio of the velocity of the 
wind to the gradient, is greater for N.E. winds and in summer 
than for S.W. winds and in winter; together with the circum- 
stance that the temperature decrement, and therefore also the 
facility with which local ascension and descension currents may 
be formed, is greater under the former conditions than under 
the latter. 
2. That simultaneously with the diurnal increase in the velocity 
of the lower layers of the atmosphere, those above appear to be 
retarded. 
3. That on stations near the earth’s surface the curve of abso- 
lute humidity reaches its minimum about the time of maximum 
wind-velocity, while at elevated stations, such as the Faulhorn, 
the humidity reaches its maximum at the same time. 
In fact it may be concluded, as Képpen graphically puts it, 
‘*that the greater the difference of the temperature of the air in 
a vertical direction, the smaller are the differences in the humidity, 
barometric pressure, and motion of the air, and that in the early 
hours of the afternoon the inhabitants of plains are placed to a 
certain extent on a higher, and the dwellers of Alpine heights on 
a lower, level, relatively to these elements.” 
E. DouGLAs ARCHIBALD 
* “Die tagliche periode der Geschwindigkeit und Richtung des Windes,’” 
September heft, 1879. 
= Meyer's formula in English measure is 7 = 7, (tr +°0014/), where » 7, are 
the friction coefficients at ¢° and 32° Fahr. respectively. 
NATURE 
461 
The Large Meteor of March 2, 1883 
THE meteor described by Mr. R. W. S. Griffith in the last 
number of NATURE was also observed at Bristol and Bath. At 
the latter place it was seen by Mr. J. L. Stothert at gh. 33m. 40s., 
passing in the direction from a Hydra to 7 Canis Majoris. The 
brilliancy of the meteor was equal to twice that of Venus ; 
colour yellow ; motion slow ; no train. Comparing this obser- 
vation with that obtained by Mr. Griffith, it would seem that 
the meteor probably belonged to a radiant point near Lyra, 
rising in the north-north-east at the time of its appearance. A 
meteor shower was observed by the writer on March 14, 1877, 
between 14h. 12m, and 15h. 43m. from the point a 277°, 
6 25°+, the members of which were somewhat slow and devoid 
of streaks or trains, and the fireball of March 2 last appears to 
have belonged to the same stream. 
It would be important to hear of additional observations of 
this meteor. Its considerable brightness, and the fact that it 
appeared at a time when it must have been widely observed, 
lead me to hope that many other records of its path have been 
preserved. In all such cases it is very desirable to give the 
R.A. and Dec. + or — of the beginning- and end-points of the 
observed path. Descriptions by the stars or compass-bearings 
are likely to be less accurate, and are often difficult to reduce. 
In the Odservatory for September, 1879, p. 129, I mentioned 
that “‘during the first four days of March fireballs have been very 
numerous, especially on the Ist, 2nd, and 4th.” This meteoric 
epoch is therefore well confirmed by the fireball of the 2nd inst. 
which it is hoped will aid us in determining one of the chief 
radiant points of the date. W. F. DENNING 
Bristol, March 12 
A VERY brilliant meteor was seen here on March 2 at 9.35 p.m. 
It burst forth in the immediate neighbourhood of Sirius, and 
passed downwards to the west at about an angle of 40° from the 
perpendicular, disappearing after a course of about 25°. Its light 
was so strong as to make the distant trees, fields, and hedges 
perfectly visible, brighter than the brightest moonlight. Its 
colours also were very decided, changing quickly, much as does 
Sirius to the naked eye, but showing more of the violet at first, 
and afterwards more of the red. jos iF 
Capel, Surrey 
On the Movements of Air in Fissures and the 
Barometer 
I sHOULD be glad to add to my article “‘On the Movements 
of Air in Fissures and the Barometer” (NATURE, vol. xxvii. 
Pp. 375) a reference to an instrument devised by Mr. Whitehouse, 
and described in 1871 before the Royal Society (Prec. Roy. Soc. 
vol. xix. p. 491). The apparatus, which was intended to record 
minute variations of atmospheric pressure, consisted of two 
hydraulic chambers, connected by a tube or siphon, and buried 
inthe ground. One of the chambers was left open at the top 
and exposed to atmospheric pressure, the other was closed and 
removed from such pressure; the difference in the level of the 
water in the two was a measure of the variation in the atmo- 
spheric pressure. This instrument reproduces those conditions 
to which the oscillation of the water-level in certain chalk-wells, 
coincident with the barometic changes, has been attributed. It 
was believed by the inventor that by its aid he had been able to 
detect atmospheric waves or pul ations at a distance from a 
storm-centre ; it has not however come into scientific use. 
I may further add to my brief allusion to colliery explosions a 
reference to the paper by R. H. Scott, M.A., F.R.S., and W. 
Galloway, Mining Engineer, entitled ‘‘On the Connection 
between Explosions in Collieries and Weather” (Proc. Roy. Soc. 
vol. xx. p. 292, 1872). A, STRAHAN 
28, Jermyn Street, March 10 
THE PITT-RIVERS COLLECTION 
T will be remembered that some time past Major- 
General Pitt-Rivers, F.R.S., most munificently offered 
his far-famed Anthropological Collection to the University 
of Oxford on the condition that the University should 
erect a building adequate to contain it and display it 
properly. On Wednesday, the 7th ult., a vote was passed 
by Convocation authorising the Curators of the Univerity 
