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530 
NAT ORE 
[ Oct. 1, 1885 
another condition, the boundary being held firm? Prof. Reynolds 
replied that he believed that he had got the result that it could 
not be done if we have a continuous medium. As other prob- 
lems for solution, Sir W. Thomson suggested the theory of the 
hour-glass—what fixes the constant time for the sand running ? 
and why does a substance sink deeper in a quicksand than in a 
viscous fluid of the same density ? 
On Calculating the Surface-Tensions of Liquids by means of 
Cylindrical Drops or Bubbles, by Prof. Pirie-—There are two 
methods by which the surface-tension of liquids are calculated. 
One involves the measurement of the height to which the liquid 
rises in a cylindrical tube of known diameter. The other in- 
volves the measurement of the height of a certain point of a 
drop of the liquid above a flat surface upon which it is placed. 
This point is the point of contact of the tangent plane when it 
becomes vertical. The former method is objectionable, because 
the results might be vitiated by the presence of a very small 
quantity of grease in the tube, or by electrification, &c. The 
latter, too, is not in a satisfactory state. Gay Lussac’s results 
were in no degree different from those obtained by the ordinary 
method. Quincke’s measurements are good, but his mathematics 
are misleading. To obviate the mathematical difficulties the 
author makes use of long drops—that is, drops obtained 
by placing portions of the liquid upon a concave cylindrical 
surface. The advantage is that the differential equation used 
in the calculation is immediately integrable. In remarking upon 
this paper Prof. Stokes said that Worthington has shown, 
by extending Quincke’s result, that the theory agrees with 
experiment. 
On the Surface-Tension of Water which contains a Gas dis- 
solved in it, by Prof. Pirie.—-This question is important, for no 
liquid is usually free from gas in solution. Prof. Pirie finds that 
the surface-tension is unaltered so long as the specific gravity 
of the water is unaffected by the dissolved gas. It is strongest 
in the pure liquid. 
On the Thermodynamic efficiency of Thermopiles, by Lord 
Rayleigh.—The question has often arisen whether or not the 
dynamo may be replaced by an arrangement of thermopiles. 
There is a great difficulty due to the conduction of heat. Let ¢ 
and /, be the temperature of the hot and cold junctions; e¢ the 
electromotive force of one pair per degree Centigrade, and Z the 
total E.M.F., hence we have 
ne (t—t)=E£. 
From this equation the author obtains by means of Joule’s 
law the expression 
ne(¢—t,)? 
4, 
for the useful work done externally. And again, if 7, 7, 04, », 
represent the specific electric resistance and the cross-sectional 
area of the metal bars, while / is their length, 
To obtain the efficiency the above work must be compared with 
that done by the apparatus regarded as a perfect heat engine 
working between the same temperature. The ratio is 
a2) Ct) 
t@\o, on/\7, 7s 
where 2’, v7, are the specific thermal resistances. The effi- 
ciency therefore is independent of (¢—4,), of 2, and of 7; and 
also of the absolute values of 0), o2, 7, 7), 7, and 7's. 
Putting in numerical values for a thermopile of iron and 
German silver, Lord Rayleigh got 300 as the value of the above 
ratio. Since e? is involved, this number may be somewhat 
reduced ; but high va es of e are usually associated with high 
internal resistance. There is therefore no possibility of the 
thermopile becoming a useful generator of electricity on a large 
scale. 
On Molecular Distances in Galvanic Polarisation, by Mr. J. 
Larmor.—Mr. Larmor’s method inyolves the electro-chemical 
equivalent of the liquid used, and so differs from the two 
methods previously adopted. He has obtained extremely 
accordant results. 
Cootinys of Wires in Air and Vacuum, by Mr. J. T. Bottomley. 
—Mr. Bottomley finds that the medium has a most marked 
cooling effect. An electric current passed through a wire, when 
surrounded by air at atmospheric pressure, heated it only to 
Be 
Gros 
feb ( 
80° C. But when the air-pressure was of an atmo- 
19 (10)° 
sphere, the wire became red hot. The temperature did not alter 
much until the pressure became I-rooth of an atmosphere. 
An Account of Levelling Operations of the Great Trigono- 
metrical Survey of India, by Major A. W. Baird.—This paper 
opened with an account of the methods formerly used in the 
determinations of relative height by the survey. The errors 
affecting these methods and the means adopted for their elimina- 
tion were then pointed out. Various lines of level carried out 
to connect tidal stations lying north and south indicated a differ- 
ence of sea-level at the stations. This difference cannot be due 
to false levelling of the instruments produced in consequence of 
the illumination of the spirit-level by the sun, for the same end 
of the line was not always brought out highest, and along one 
line no difference of level was perceptible. The discrepancy in 
one case amounted to three feet along the line from Bombay to 
Madras. The two weakest parts of this line were re-levelled, 
giving the same results as before. Consequently it would appear 
that the error is caused by local attractions influencing the 
instruments in greater degree than the more distant ocean. 
On the Rainfall of the British Islands, by Mr. A. Buchan.— 
Mr. Buchan pointed out that the greatest differences in local 
climates arise from differences in the rainfall. For example : 
the mean temperatures of Skye and the Moray Firth coasts for 
any month are not much different, but the rainfall in Skye is 
about four times that at the Moray Firth. The former is one of 
the latest and poorest grain-producing districts in Scotland, and 
the latter is just the reverse. The inquiry was based on ob- 
servations of rainfall made at 1o8o stations in England and 
Wales, 547 in Scotland, and 213 in Ireland. They extend from 
the year 1860 to the year 1883. The regions of heaviest rainfall, 
giving an average of 80 inches or upwards annually, were four: 
Skye and a large portion of the mainland to the south-east as 
far as Luss, on Loch Lomond ; the greater part of the Lake 
District ; a long strip, including the more mountainous part of 
North Wales ; and the mountainous district in the south-east of 
Wales. The West Highlands is the most extensive region of 
heavy rainfall in the British Islands. Its mountainous coast-line 
faces the rain-bringing winds of the Atlantic, and the air, being 
cooled in its passage up the lochs and valleys, the moisture is 
precipitated. At Glencoe, in this district, the heaviest rainfall 
in Scotland occurred—128°5 inches. The smallest rainfall was 
in a large portion of the south-east of England. The average 
rainfall for the last half of the period from 1860 to 1883 was 
comparatively high, chiefly in the eastern districts. 
On a Remarkable Occurrence during the Thunderstorm of 
August 6, 1885, by Mr. W. H. Preece.—A house at St. Cuth- 
bert’s, ten miles from Wolverhampton, is connected with that 
town by telephone, and is also lighted by electricity. The 
dining-room was lighted by a single lamp in multiple are with 
some others. The telephone wire was connected to the light- 
ning-conductor as an earth. When the storm occurred, the 
dining-room lamp flashed up and went out, while a loud report 
was heard. The lightning-rod made bad earth, and it is be- 
lieved that it had been struck, and that part of the discharge 
had entered the telephone circuit and then sparked across to the 
electric-light circuit. It did not seem to have divided, but to 
have passed entirely along the one branch, including the dining- 
room light, the platinum wire of which was volatilised and 
deposited on the interior of the glass, forming a good mirror. 
M:teorology of Ben Nevis, by Mr. A. Buchan. —Mr. Buchan 
remarked that Ben Nevis possesses great advantages as a 
meteorological station because of its great height and its summit 
being only about four miles horizontally distant from a sea-level 
station. Also it is in the track of the Atlantic storms, which 
exercise so great an effect on the weather of Europe, especially 
in autumn and winter. The observations made on the moun- 
tain are for the purpose of determining more fully the great 
movements of the atmosphere and the dependence of the 
weather upon them. Mr. Buchan called attention to the great 
importance of abnormal values in the thermometric and hygro- 
metric observations especially. The recurring periods of warmth 
characteristic of Ben Nevis do not occur at lowerstations. The 
fohn peculiar to Switzerland occurs on Ben Nevis, and is 
clways associated with heavy rainfall in the neighbourhood. 
When a cyclone prevailed at the foot of the mountain there is 
on anticyclone at the top, and wice versd. 
On some of the Laws which Regulate the Sequence of Mean 
Temperature and Rainfall in the Climate of London, by Dr. 
