116 
NATURE 
[May 29, 1902 
self-driving arrangement, and ithat the use of a separate motor 
will remedy these defects. The trials referred to were made 
with various forms and sizes of siren and several instru- 
ments sounded on the reed principle, the result being 
that the reed instruments proved greatly inferior to the 
siren instruments in loudness and penetrating power. It is 
contended by some that the reed principle as applied for the 
production of loud sounds has never yet been done justice to, 
and that with proper development a reed instrument could be 
made to yield sounds as powerful and penetrating as those of | 
the siren; but, as Mr. Price Edwards points out, the reed 
instruments tried, and which were supposed to be the most 
effective types of that form of sound producer in existence, were 
not able to approach the sirens as regards efficiency for coast 
fog-signal purposes. Ifa reed instrument could be brought up 
to an equality with a siren in respect of sound power, it would 
probably be more economical than a siren in working. The 
question of trumpets received some special consideration at St. 
Catherine’s, a new form of trumpet designed by Lord Rayleigh 
having been experimentally tried there. Lord Rayleigh had 
observed that with the conical trumpets of circular section 
usually employed there was a liability to some interference of 
the sound waves issuing from the mouth, caused by the difference 
in distance of the nearest and furthest parts of the mouth, 
whereby the waves were likely to get out of step and thus cause 
interference. Tle also pointed out that a good deal of sound 
was sent to the zenith from the mouth of circular section, which 
sound was certainly wasted. To remedy these defects, Lord 
Rayleigh’s idea is to make the horizontal diameter at the mouth 
only half the length of the sound wave generated by the sounding 
instrument, and that the vertical diameter should be elongated 
to two wave-lengths or more, thus producing a mouth of ellip- | 
tical section. The tendency for the waves issuing from the mouth 
to get out of step would thus be reduced to a minimum, and 
the narrowness of the mouth at top and bottom would offer but | 
little scope for the sound to be projected upward or immediately 
downward. So far as the trials went, Mr. Price Edwards tells 
us that the effects produced were most encouraging, and it is 
now intended to set up this elliptical trumpet for practical trial 
at a fog-signal station. ‘The mushroom form of trumpet for an 
all-round signal has been largely used for lightships. Instead 
of a long horizontal trumpet, or a vertical one with the head 
bent over (capable of being turned in any direction), the trumpet 
is fixed vertically with its mouth directed upward. Just above 
and in the centre of this open mouth is fixed an inverted cone, 
and the sound issuing from the trumpet strikes the curved sides 
of the cone and is reflected out with equal force all round the 
horizon. The trials made with this form of trumpet showed 
that it was well adapted for the purpose for which it had been 
designed. 
But however powerful and characteristic the sound-producing 
instruments may be, the conditions of the atmosphere have 
very much to do with their effectiveness. An opposing wind, 
as is well known, shortens the range of penetration of the 
most powerful sound. An instance is given by Mr. 
Edwards when the sound of a siren was on one day heard for a 
distance of more than twenty miles, while on another day, with 
Price | 
a little opposing wind and a noisy sea, the sound of the same | 
instrument was not heard beyond a distance of one mile and 
a quarter. Fortunately, when sound signals are most needed, 
viz. in foggy weather, obstructive influences seldom occur ; 
the air is generally still, the sea quiet, and a homogeneous 
condition as regards temperature and moisture exists, all 
of which conditions are favourable for the propagation of 
sound. It does not seem at all probable that the acoustic 
clouds of Prof. Tyndall are formed when fog prevails; indeed, 
they appear to want hot sun, causing evaporation from the 
sea surface, which produces areas of varying temperature and 
density. Two remarkable phenomena have been experienced 
in connection with the experiments at St. Catherine’s for which 
no satisfactory explanation is yet forthcoming. In the one case 
it was found that at times there was a sort of hiatus in the 
passage of the sounds. Thus the observers on board the Trinity 
yacht /renze would be in full hearing of the sounds at a mile 
distance from the instruments. On proceeding out, the sounds 
would very soon fall away in strength until at a distance of 
between two and three miles they would be very faintly heard 
or lost altogether. Proceeding further out on the same line 
of bearing, the sounds would be gradually recovered, until a 
little beyond three miles they would again come into full hear- 
NO. 1700, VOL. 66] 
ing and be carried as loud and distinct sounds for a considerable 
distance. The question is, what becomes of the lost sound, 
and what is the influence which renders the area in question 
‘a silent area’? ? The phenomenon apparently does not occur 
frequently, for very many times the observers went over the 
same space without experiencing any such hiatus of sound. Mr. 
Price Edwards suggests that to solve the question prolonged 
and continuous observation would be necessary in all parts of 
the sea area over which the sounds are projected—at the sea 
surface, on the deck of a vessel, and at varying distances 
upward by means of a captive balloon. It is of importance to 
determine, if possible, the cause of this intermission of audibility, 
in order that it may be prevented or guarded against when the 
sounds are being promulgated as official warnings to mariners. 
The other noteworthy phenomenon which occurred at St. 
Catherine’s and on previous occasions when sound signals have 
been tested by observation at sea were the aérial echoes. With 
a smooth sea and still atmosphere, the direct sounds from the 
sirens were immediately reinforced by powerful echoes from the 
sea. Mr. Price Edwards describes them as starting from a 
point on the horizon corresponding to the prolongation of the 
axis of the trumpet from which the sound proceeded, and with 
great rapidity spreading out over the sea expanse as though a 
scattered army of trumpeters in quick succession sounded their 
blasts from all parts of the horizon. Carefully timed, the echoes 
lasted at times for 30 seconds, or ten timesas long as the original 
blast. Prof. Tyndall suggested that ‘‘ the duration of the echo 
isa measure of the atmospheric depth from which it comes.” If 
this be so, the length and strength of the echoes might afford 
a general indication of the relative penetrating power of the 
sounds of different instruments. With a disturbed atmosphere 
and an agitated sea surface, the echoes were very short or not 
heard at all. It is noteworthy that both the silent area and the 
aérial echoes occur chiefly in quiet weather, and that disturbance 
of air or sea appears to be antagonistic to their manifestation. 
An important conclusion appears to have been arrived at in 
regard to the most suitable note pitch for the blasts of sirens or 
reed horns. In fog—as has been stated—the meteorological 
conditions are usually equable, and when such is the case a low- 
pitched note is found to be more effective than a high-pitched 
one; on the other hand, when air or sea is disturbed, the. 
higher pitched notes seem to be rather less obstructed by the 
opposing influences, although the advantage is not very great. 
Having regard to the fact that the sounds are only required for 
use in foggy weather, a low-pitched note of about 98 vibrations 
per second (which is that which was heard plainly more than 
twenty miles away) is perhaps the best for the blasts of a 
siren fog signal. In this connection it should be mentioned 
that in order to obtain the best effect from an instrument it is 
essential that the note given by the sound producer should, if 
possible, be in unison with the proper note of the associated 
trumpet, otherwise the issuing sound is apt to be gruff and 
discordant. 
SEA TEMPERATURE AND SHORE CLIMATE. 
N Mr. W. N. Shaw’s paper ‘‘On the Seasonal Variation of 
Atmospheric Temperature in the British Isles” (Proc. Roy. 
Soc., vol. lxix., pp. 61-85), it is stated that it seems ‘‘ probable that 
the ocean plays a paramount part in the causation of the second- 
order temperature effect which we experience in these islands. 
. . . Whether this variation of the temperature of the water 
which surrounds these islands is the cause of the atmospheric 
second-order variation, or whether it is only another effect of 
the same fundamental cause, does not appear, but in view of 
the fact that the marked second-order effect is not seen at 
Continental stations, it would seem not unlikely that the ocean 
temperature is the immediate cause of our second-order periodic 
temperature variation. All the successive stages of 
temperature change are delayed by the effect of the sea... . 
The effect of the sea is to delay the seasons.” Of course, it is 
a very old belief that the vicinity of the sea affects the tempera- 
ture of a climate, moderating the heat of summer and the cold 
of winter, but the ideas on the subject have been of the usual 
vague popular character. What is curious is that it has taken 
so long to initiate some investigation designed to discover what 
may be the nature of the relationship between the temperature 
of the sea and that of the air over the adjacent land. Although 
the North Atlantic is the most frequented of the great oceans, 
