42) 
of the finest particles of Sahara sand, while others looked for its 
origin on laterile ground. 
The value of the occurrences of falls of dust is of special 
moment meteorologically, because they afford us a means of 
obtaining further knowledge of the actual movements of the air 
currents in the higher reaches of our atmosphere which cannot 
be gained by any other such direct methods. Much valuable 
information was obtained of the movement of the air at great 
heights by the dust that was ejected during the eruption of 
Krakatoa, and as this volcano is situated near the equator, 
where the air currents have a great tendency to rise directly 
away from the earth’s surface, the conditions were favourable 
for the dust reaching an extraordinary elevation. 
Nevertheless, whether the falls owe their origin to dust 
storms in a desert or eruptions of large volcanoes, it is of great 
importance to meteorological science that they should be, not 
only accurately observed, but recorded and discussed. Fortu- 
nately, the fall in the present instance occurred where a great 
amount of useful data could be, and was, secured. In the 
vandling of this material the authors are to be congratulated, 
for besides considerably increasing our knowledge of the way in 
which the dust is transported and enlightening us on other 
peculiarities of this interesting phenomenon, they have given us 
a volume which will serve as an excellent example for future 
recorders and observers. Wejenos) Le. 
BRITISH VERSUS AMERICAN LOCOMOTIVES. 
NOTEWORTHY Parlimentary paper has recently been 
issued containing correspondence respecting the comparative 
merits of British, Belgian and American built locomotives 
sunning on the Egyptian railways. The paper is full of interest 
to the locomotive engineer, bearing out as it does the unsatis- 
factory results obtained with American locomotives on British, 
Colonial and Indian railways when compared with the English 
design of engine, and, what is more, these unsatisfactory results 
are in all cases certified by the representative of the American 
firm of locomotive builders, as well as by an official appointed 
by the Egyptian railway authority, so there can be little doubt 
as to their accuracy. 
Probably the most interesting report in the series is that by 
Mr. Trevithick, the locomotive engineer, who says:— 
“©The Mechanical Department of the Egyptian State Railways 
has recently made some interesting comparative trials between 
British and American locomotives of the same weight and 
power. These comparisons have been carried out under 
exceptionally favourable circumstances, inasmuch as the loco- 
motives employed were typical of their respective countries 
in design and manufacture, and the trials were personally 
conducted, and the results conjointly signed, by a representative 
sent out by the American builders and a locomotive inspector 
of the Egyptian Railway Administration. 
‘The first set of trials, consisting of eight runs extending over 
1034 miles, was between goods engines, and, in order to secure 
similar loads and to be able to gradually increase the weight of 
trains to the maximum that the respective engines could 
satisfactorily draw, the material transported consisted chiefly of 
coal. 
“©The total amount of coal consumed in the eight trips by 
the British engines was 22°84 tons, which works out at an 
average of 49 4lbs. per mile, whilst the American engines con- 
sumed 28°69 ton:, an average of 62 lbs. per mile ; in other words, 
for every 100 tons of coal consumed by the British engines the 
American engines burnt 125°4 tons, 7.e. an excess of 25*4 per 
cent. This economy was effected by the British engines, 
although they drew a hagvier average load, to the extent of 
14°2 per cent. than the American, the average train taken by the 
British engines being 57 trucks, or $68 tons, as against 54 trucks, 
or 76o0tons, the average train taken by the American. The 
maximum load taken by each make of engine was 61 trucks. 
‘“« These trials were followed by others between passenger types 
of engines, extending over 1345 miles ; each make ran an equal 
number of trips with practically similar formation of trains, with 
the result that the British engines consumed a total of 1847 tons 
of coal, or an average of 30°7 lbs. per mile, as against a total of 
27°8 tons, or an average of 46°3 lbs. per mile, in the case of the 
American engines, which means that where the British engine 
consumed 100 tons, the American engine consumed 150 tons, or 
50 percent. more. Sucha difference at 1/, 145. 2d. per ton, the 
NO. 1697, VOL. 66] 
NATURE 
[May 8, 1902 
average price paid last year by the Railway Administration, — 
represents an additional yearly cost per engine of 400/.; which is’ 
to say that these ten American engines would cost in coal in one 
year 4000/. more than the ten British engines, an amount almost 
sufficient to buy two new ones.” 
The above extract from Mr. Trevithick’s report conclusively 
proves that the British type of locomotive is well able to hold its 
own in the three important matters of fuel and oil consumption, 
and cost of repairs. Much has been written lately on the 
standardisation of the locomotive, but in a progressive age this 
appears to be unnecessary, since the locomotive of yesterday 
must always be out of date. Much can, however, be done to assist 
locomotive builders in the way of standardisation of specifications 
and, more particularly, of the test requirements for the material. 
It is absurd to think that consulting engineers cannot agree as 
to the best test requirements for, say, acrank axle or a steel 
boiler plate. With standard tests the locomotive builders could 
buy the material more cheaply, obtain quicker deliveries from 
the makers, and, probably, in their turn take less time to complete 
an order. 
INTEKFERENCE OF SOUND.' 
FoR the purposes of laboratory or lecture experiments it is 
convenient to use a pitch so high that the sounds are 
nearly or altogether inaudible. The wave-lengths (1 to 3 cm.) 
are then tolerably small, and it becomes possible to imitate 
many imteresting optical phenomena. ‘The ear as the percipient 
is replaced by the high-pressure sensitive flame, introduced for 
this purpose by Tyndall, with the advantage that the effects are 
visible to a large audience. 
Asa source of sound a ‘‘ bird-call” is usually convenient. A 
stream of air from acircular hole in a thin plate impinges 
centrically upon a similar hole in a parallel plate held at a little 
distance. Bird-calls are very easily made. The first plate, of 
I or 2 cm. in diameter, is cemented, or soldered, to the end of 
a short supply tube. The second plate may conveniently be 
made triangular, the turned-down corners bzing soldered to the 
first plate. For calls of medium pitch the holes may be made 
in tin plate. They may be as small as 4mm. in diameter, and 
the distance between them as little as 1 mm. In any case the 
edges of the holes should be sharp and clean. There is no 
difficulty in obtaining wave-lengths (complete) as low as I cm., 
and with care wave-lengths of 0°6 cm. may be reached, cor- 
responding to about 50,000 vibrations per second. In .experi- 
menting upon minimum wave-lengths, the distange between the 
calland the flame should not exceed 50 cm., and the flame 
should be adjusted to the verge of flaring (‘‘ Theory of Sound,” 
2nd ed., § 371). As most bird-calls are very dependent upon 
the precise pressure of the wind, a manometer in immediate 
connection is practically a necessity. The pressure, originally 
somewhat in excess, may be controlled by a screw pinch-cock 
operating on a rubber connecting tube. ie 
In the experiments with conical horns or trumpets, it is 
important that no sound should issue except through these 
channels. The horns end in short lengths of brass tubing which 
fit tightly to a short length of tubing (A) soldered air-tight on 
the face of the front plate of the bird-call. So far there is no 
difficulty ; but if the space between the plates be boxed in air- 
tight, the action of the call is interfered with. To meet this 
objection a tin-plate box is soldered air-tight to A, and is stuffed 
with cotton-wool kept in position by a /oose/y fitting lid at c. 
In this way very little sound can escape except through the tube 
A, and yet the call speaks much as usual. The manometer is 
connected at the side tube D. The wind is best supplied from 
a gas-holder. y 
With the steadily maintained sound of the bird-call there is 
no difficulty in measuring accurately the wave-lengths by the 
method of nodes and loops. A glass plate behind the flame, 
and mounted so as to be capable of sliding backwards and 
forwards, serves as reflecting wall. At the plate, and at any 
distance from it measured by an eve number of quarter wave- 
lengths, there are nodes, where the flame does not respond. At 
intermediate distances, equal to odé multiples of the quarter 
wave-length, the effect upon the flame is a maximum. For the 
present purpose it is best to use nodes, so adjusting the sensi- 
tiveness of the flame that it only just recovers its height at the 
1 A Discourse delivered at the Royal Institution on Friday, January 17, 
by the Right Hon. Lord Rayleigh, F.R.S. 
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