Art. 12.-THE SOUND OF BIG GUNS.

FOR a century at least, it has been known that the sound of gun-firing may be heard to great distances. The conditions, especially the direction of the wind at the time, must be favourable; but, granted those conditions, there is no reason why the sound should not be heard more than a hundred miles from its source. The firing at Waterloo, it is reported, was heard in the eastern districts of Kent; and there are no reasons for discrediting the statement, though the distance traversed must be between 130 and 140 miles. There are not, indeed, observations forthcoming from the intermediate area occupied by sea; but the sound of very distant firing possesses a distinctive character of its own, and it is unlikely that, on this particular Sunday morning, heavy firing took place elsewhere than at Waterloo. Again, on another Sunday morning forty-nine years later (June 19, 1864), when the 'Alabama' was sunk by the 'Kearsarge' nine miles off Cherbourg, the sound of the guns was distinctly heard near Exeter (108 miles from Cherbourg) and near Bridgwater (125 miles). Similar observations have been made since the beginning of the present war, for there can be little doubt that the sounds of artillery actions in Flanders have been audible in the south of Holland and the south-eastern counties of England; the paths traversed by the sound-waves in these cases being, roughly, 100 and 120 miles in length. The interest revived by such observations may perhaps justify a more detailed reference to our knowledge of this subject and of the conditions which favour the transmission of sound-waves by the atmosphere.

It is evident that observations so sporadic as these are of little value for our purpose. They must in any case be far more numerous. They must come from places at many different distances and in various directions from the origin. The most distant places at which the sounds are heard should not be widely separated from others. It is not easy to fulfil these conditions unless preparations can be made beforehand; and the opportunities for this are infrequent. Towards the close of the last, and the beginning of the present century, there were, however, three occasions on which it was possible to

collect the desired observations. There was a great naval review at Spithead on June 26, 1897, in celebration of the late Queen Victoria's diamond jubilee. On July 18, 1900, when the French president, M. Loubet, visited Cherbourg, a sham fight was held in his honour. A few months later, on Feb. 1, 1901, when the body of Queen Victoria was brought from the Isle of Wight to Portsmouth, minute-guns were fired from the battle-ships which lined the route of the royal yacht.*

In the naval review of 1897, the fleet consisted of 165 men-of-war of all classes. When the royal yacht entered the lines, the first shot was fired from the flag-ship. The other ships followed in turn, each firing a royal salute of twenty-one guns. The guns used were of various sizes, the heaviest being a 6-inch breechloading gun firing a blank charge of 7 lbs. They gave rise to a dull crackling noise at a short distance from the lines, but, as ship after ship took up the salute, the firing grew animated and the roll of the guns louder. This lasted for about five minutes, when the report of the last gun died away. At some distance from Spithead, the sound of the firing changed in character. Distinct reports were heard at the beginning and end of the salute as far as Farnham, 34 miles from Spithead. At greater distances, the sound was a dull, continuous roar, with occasional booms from the heavier guns.

At the time of the review, there were light but variable breezes prevailing over the south of England, mainly from the east, almost everywhere between north-east and south-east. The effect of these winds on the propagation of the sound-waves is very marked. To the east, the sound was heard as far as Framfield (57 miles), to the north-east it was heard at Wimbledon (62 miles), to the north at Bloxham Green near Banbury (88 miles), to the west at Wellington in Somerset (93 miles), and probably at Shebbear near Torrington (135 miles). Thus, though the easterly wind was only light, the sound of the guns was heard about twice as far with the wind as in the opposite direction.

* The distance to which the firing of heavy guns is heard': 'Nature,' vol. 62, 1900, pp. 377-379; 'On the audibility of the minute guns fired at Spithead on February 1' [1901]: 'Knowledge,' vol. 24, 1901, pp. 124-125.

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On Jan. 22, 1901, Queen Victoria died at Osborne. Ten days later her body was borne from Cowes to Portsmouth, the course of H.M.S. 'Alberta' lying to the south of a line of thirty men-of-war, running from east to west, and ranging from third-class cruisers of about 2000 tons to battleships of 14,900 tons. When the Alberta' left Cowes, at 3 p.m., a gun was fired from the 'Alexandra' at the west end of the line. This was followed by minuteguns from the Majestic' at the other end of the line, from which the remaining ships took their time, all firing as nearly together as possible. Each ship stopped firing as the funeral procession passed it, so that the reports gradually faded in strength. The guns used were 6-inch guns with blank charges of 7 lbs.; and though all could not be fired simultaneously, many were at times fired practically together. Thus, at a distance, a loud boom was usually heard, due to the nearly simultaneous discharge of several guns, followed by a rumble which sometimes lasted for as much as twenty seconds.

Owing to this peculiar character of the reports, and especially to their regular recurrence at minute-intervals, it was possible to trace them with confidence to great distances from Spithead. From east to north-west, and at distances from sixty to eighty miles, the places where the sound was heard are clustered closely together. Beyond the eighty-mile circle they decrease in number, but several lie between this distance and a hundred miles, and there can be little, if any, doubt that the reports were heard as far as Shelford, near Cambridge (111 miles from Spithead), St Ives in Huntingdonshire (118 miles), Holme, near Peterborough (125 miles), and Alderton, near Woodbridge in Suffolk (139 miles).

The most remarkable fact about the reports, however, is not their audibility at these great distances, but their practical inaudibility close to Spithead, Persons on steamers just outside the line of battleships heard the firing only from the vessels nearest to them. In Portsmouth, the first notice of the approaching procession came from a gun fired from the 'Victory'; and no shots were fired from vessels stationed in the harbour until the 'Alberta' had passed the whole line of battleships. It is expressly stated that not a sound was heard at Yarmouth, I. W. (10 miles), Chichester (15 miles), Fritham

Plain, near Lyndhurst (16 miles), Winchester (20 miles), Midhurst (22 miles), Bournemouth (27 miles), and Newbury (44 miles). Indeed, so far as is known, the nearest place at which any report was heard was Horley in Surrey, distant 50 miles. Thus on land the firing was inaudible for nearly fifty miles. Beyond this distance it was frequently heard. Near Chipping Norton (84 miles) it was so loud that labourers in the fields put down their spades and listened. Towards the north-east reports were clear enough to attract attention at a distance of 139 miles.

There can be little doubt that these curious anomalies are connected with the varying direction of the wind at the time. Close to Spithead it came from the west and was usually light. Near Lyndhurst there was a fresh breeze from the north-west or west-north-west. At Portsmouth the wind came from the shore. Beyond the sixty-mile circle the wind was light and was generally from the south. The effect of the wind is therefore clear. The sound-waves were heard at great distances in the direction towards which the wind was travelling. Against the wind they were totally inaudible only a few miles away.

Before proceeding to the account of the Cherbourg review, I may refer briefly to some further anomalies in the transmission of sound by the atmosphere. These are manifested more clearly in short, sudden explosions of volcanic origin than in the long rolling reports of multitudes of guns. Near the centre of the main island of Japan lies the Asama-yama, one of the most active volcanoes in the empire. The last great eruption occurred in 1783. It was followed, as is usually the case after so violent an outburst, by a prolonged interval of quiescence, which now seems drawing to a close. The last ten or eleven years, and especially those from 1911 onwards, have been marked by numerous explosions, which are no doubt the forerunners of another catastrophe. With the methodical organisation which is as characteristic of Japan as of the great empire with which we are at war, these premonitory symptoms are being carefully studied by Prof. Omori and a numerous band of assistants. Some of his most interesting observations relate to the areas over which the detonations are heard. As a

rule, they diverge from the Asama-yama as apex towards the east and south-east. Towards the south they may extend to the coast, 112 miles away; towards the northeast to a distance of 168 miles; * while towards the west the sound may be inaudible at a distance of only 16 miles. This peculiar extension of the sound-area is evidently connected not so much with the variable surface-winds as with the upper winds, which during most of the year travel almost uniformly towards the east or east-south-east. In two cases the form of the sound-area is still more remarkable. It consists of two entirely detached portions, one including the Asamayama near its western margin, the other lying to the west and separated by a zone of silence fifty or sixty miles in width.

Another interesting fact recorded by Prof. Omori is that, while the original detonation is single and is heard as one sound for a distance of about 25 miles, there then occurs a zone in which the sound is double. This is followed by another zone, with its nearest margin about 75 miles from the volcano, in which three sounds are heard; and this again is succeeded by a fourth zone, 120 to 150 miles distant, in which two sounds are again heard.

Let us return to the naval review at Cherbourg on July 18, 1900, which threw further light on the problem. About 10 p.m. a sham fight took place between two portions of the French fleet, including altogether 43 vessels, of which 13 were among the largest battleships then existing. The night was very still, hardly a breath of wind could be felt, and the sea was absolutely calm. The reports were heard along the English coast from Devonshire to Sussex. From Torquay to Bognor the airvibrations were so strong as to shake the houses; and for three or four days afterwards many English newspapers contained reports of supposed earthquake-shocks. The sounds were heard at about equal distances in both directions along the coast; towards the north-west, at Budleigh Salterton, Sidmouth and Torquay (101 miles

* Great as is this distance, it is small compared with those (2014 and 2968 miles) to which the Krakatoa eruption of 1883 was heard.