

The last paper read in this Section was Ox the Rainfall of 
Scotland, and contributed by Mr. Buchan. The paper was 
illustrated by a map of Scotland, showing the average annual 
rainfall of about 200 places, many of the averages being deduced 
from observations carried on through a long series of years. Tne 
map brought ont the large rainfall in the west as compared with 
the east, a difference which was strongly marked even in the 
group of the Orkney Islands. The average rainfall in the west, 
at stations removed from the influence of hills, was from thirty- 
six to about forty inches ; but on the east coast, in similar situa- 
tions, the rainfall was as low as from twenty-four to twenty-eight 
inches. In casting the eye towards the watershed of the country 
running north and south, it was seen that in ascending towards it 
from the west, there occurred a rapid, but by no meaas uniform, 
increase ; and in descer ding from it towards the east, a rapid, 
but by no means uniform, decrease. The largest rai falls occur 
almost wholly among the hill, form'ng the watershed north of the 
Forth and Clyde. The places characterised by the heaviest rain- 
fall are, so far as observation has yet enabled us to determine, 
the following:—Glencoe, immediately under  Rest-and-be 
Thankful, 128 inches annually ; Ardlin, head of Loch Lomond, 
115 inches ; Bridye of Orchy, 110 inches ; Tyndrum, 104 inches ; 
Glen Quoich, in the south-west of Invernesshire, 102 inches ; 
and Portree, Skye, 101 inches. At no great distance from 
several of these places the rainfall is by no means excessive, thus 
pointing out an enormous difference of climate between places 
not far apart. Along the watershed of that part of Scotland 
which lies south of the Forth and Clyde, no such excessive rain- 
fall occurs, the highest hitherto observed being only 71 inches, 
Ettrick Pen Top, 2,268 feet bigh. This diminished rainfall in 
the south as compared with places similarly situated further north 
is doubtless due to the mountains of Ire'and to the south-west, 
which partially drain the rain-bringing winds of their moisture 
before they arrive at these parts of Great Britain. The distribu- 
tion of the rainfall is very instructive in many districts, as in the 
valley of the Forth, from the head of Loch Katrine to North 
Berwick, where the amount varies from ninety-one to twenty-four 
inches ; in Clydesdale, where the quantity is greatestat the head 
and foot of the valley respectively, being considerably less at 
intermediate places; and along Loch Linnhe and through 
the Caledonian Valley, where the variations of the rainfall were 
excessive. In all these districts, as well as elsewhere, many 
cases might be referred to, showing that the amount of the rain- 
fall is very far from being determined by mere height. In truth, 
it is to local considerations we must chiefly look for an explana- 
tion of the mode in which rain is distributed over any dis- 
trict; and hence, in estimating the rainfall, particularly in hilly 
districts, no dogmatic rule can be laid down which can approxi- 
mate in accuracy the result arrived at by one skilled in such 
matiers and who is at the same time well acquainted with the 
district. If those districts were shaded off in which the rainfall 
did not exceed 30 in. annually, the great grain-producing dis- 
trict of Scotland would be indicated ; and it was interesting to 
note that in those districts which produced the best wheat the 
rainiall was lower than elsewhere, being in many places as low 
as 24in. There are about fifty places at which observations 
have been made for periods varying from twenty to forty-five 
years. On comparing the average of the three driest years at 
each of these places with its average, the amount of the deficiency 
is found to vary exceedingly, being as much as one-third in some 
places and as litde as one-ninth in others. 
Mr. Bateman expre-sed his great satisfaction that Mr. Buchan 
had stuck to facts instead of theorising. He went on to say that 
the correction given for the three dry years was just as fallacious 
as the correction for altitude. A proposed rule had been laid 
down of an increase in the rainfali of one and a half per cent. 
for each 100 feet of elevation, but subsequently that one and a 
half had been changed to twoand a half. Mr. Bateman said 
that the formula for the three dry years was that for the height. 
In point of fact it was impossible to lay down any rule that 
would give accurate results. 
Mr. Symons drew attention to the fact that the ratio of the 
three dry years depended very much on the length of period in- 
volved, and showed that the epoch of dry years in the in- 
stances quoted varied almost precisely with the length of those 
averages. 
Mr. Bateman and Mr. Symons spoke strongly in favour of the 
work performed by Mr. Buchan, and of the excellent operations 
of the Scottish Meteorological Society. 
Mr, Milne Home made a few appropriate remarks in reply, 
NATURE 














MAXIMUM VELOCITY OF METEORIC STONE 
REACHING THE SURFACE OF THE EARTH 
[N Prof, Nordenskjéld’s account of the Aerolitic Shower which 
took place near Hessle, in Sweden, on the Ist of Janua 
1869, he mentions, asa remarkable fact, that stones weighing 
two pounds, which struck the ice of the Larsta-Viken, failed to 
penetrate, making holes only three or four inches deep in the ii 
and rebounding. (Vide the Academy, Dec. 15, 1870.) 
The small velocity retained by these stones at the time of 
striking the earth is, doubtless, owing to the resistance of the air, 
and, consequently, is not an indication of the velocity which they 
had upon entering the atmosphere. 
Stones thus penetrating the atmosphere from interplanetary 
space, would be moving in a resisting medium under the joint 
influence of their original velocity of translation and the constant 
action of terrestrial gravity. In the case of small masses, the 
resistance of the medium would very speedily produce retarded 
motion ; and before traversing twenty or thirty miles of air, they 
would probably move with a velocity approximating uniformity, 
and under the action of gravity alone. In other words, they 
would gradually lose their original velocity of translation, and, 
descending, nearly or quite vertically, under the action of gravity, 
would ultimately attain a maximum velocity under the opposing 
influences of the resisting and accelerating forces, and then descend 
to the earth with this uniform velocity. , 
Thus, for example, a rifle bullet shot obliquely into deep water, | 
would very soon lose the horizontal component of its velocity, 
while the vertical motion would be so rapidly retarded that, at a 
comparatively short distnce below the surface of the water, it 
would begin to descend vertically with the very moderate uniform 
motion resulting from the resistance of the liquid and the constant 
action of gravity. 
In like manner, no matter how great the velocity with which 
a meteoric stone enters the atmosphere, the enormous resistance 
which it encounters must operaie ultimately to produce a similar 
result, although, in some cases of oblique incidence, the hori- 
zontal component of velocity is not entirely lost before reaching 
the earth. 
It is well known that this maximum or limiting velocity of a 
falling body is attained when the required velocity is such that 
the resistance is at each instant equal to the weight of the moving 
body. In the case of small masses moving in the air, it may be 
shown that this velocity is quite moderate. 
The principles of dynamics furnish the means of determining 
the resistance of a given body moving in a medium of given 
density when the size of the body and its velocity are known. 
Let 4 = area of cross-section of body at right angles to direc- 
tion of motion. 
D = weight of unit volume of medium (air). 
wv = velocity of moving body (meteoric stone). 
g¢ = acceleration by gravity in a unit of time. 
# =a constant co-efficient, deduced from experiment, de- 
pending upon the shape of the moying body. 
Then we have, 
gt 
Resistance = & x A x Dx — 
a 
2g 
Hence, by the conditions under which, as above given, v becomes 
a maximum, if w= weight of the moving body or stone, we 
have, 
hx Ax Dx C=wsv= XE ZEEE (a) 
ae eX AaK ED 
Applying this formula (a) to the case of a meteoric stone weigh- 
ing two pounds moving in the air :—let us assume it to be a cubical 
mass, having a specific gravity of 3 in relation to water as unity. 
Then its volume = 18°482 cubic inches, and the area of one of 
its faces = 6°9903 square inches=0'048544 square feet. Hence, 
assuming the resistance to act at right angles to the face of the 
cube, and taking the pound and foot as units, we have— 
A = 0'048544 square feet. 
D = 0 0807238 pounds = weight of cubic foot of air at 0° C, 
w=2 Ty = 5) », stone, 
g =32'1928 feet per second. 
v = required maximum velocity in feet per second, 
