458 



NATURE 



{April \, 1878 



axis of the instrument the sound was about as effective as that 

 of the 8-oz. rocket. But in a direction at right angles to the 

 axis, and still more in the rear of this direction, the syren fell 

 very sensibly behind even the 2-oz. rocket. 



These are the principal comparative trials made between the 

 gun-cotton rocket and other fog-signals ; but they are not the 

 only ones. On August 2, 1877, for example, experiments were 

 made at Lundy Island with the following results. At two miles 

 distant from the firing point, with land intervening, the 18- 

 pounder, firing a 3 lb. charge, was quite unheard. Both the 

 4-0Z. rocket and the 8-oz. rocket, however, reached an elevation 

 which commanded the acoustic shadow, and yielded loud reports. 

 When both were in view, the rockets were still superior to the 

 gun. On August 6, at St. Ann's, the 4-oz, and 8-oz. rockets 

 proved superior to the syren. On the Shambles Light-vessel, 

 when a pressure of 13 lbs. was employed to sound the syren, the 

 rockets proved greatly superior to that instrument. Proceeding 

 along the sea-margin at Flamboro' Head, Mr. Edwards states 

 that at a distance of I5 mile, with the 18-pounder gun hidden 

 behind the cliffs, its report was quite unheard, while the 4-oz. 

 rocket, rising to an elevation which brought it clearly into view, 

 yielded a powerful sound in the face of an opposing wind. 



On the evening of February 9, 1877, a remarkable series of 

 experiments was made by Mr. Prentice, at Stowmarket, with 

 the gun-cotton rocket. From the report with which he has 

 kindly furnished me I extract the following particulars. The 

 first column in the annexed statement contains the name of the 

 place of observation, the second its distance from the firing-point, 

 and the third the result observed : — 



Stoke Hill, Ipswich ... 10 miles Rockets clearly seen and sounds dis- 

 tinctly heard 53 seconds after the 



flash. 

 Melton" 15 ,, Signals distinctly heard. Thought at 



first that sounds were reverberated 



from the sea. 

 Framlingham 18 ,, Signals very distinctly heard, both in 



the open air and in a closed room. 



Wind in favour of sound. 

 Stratford. St. Andrews.. 19 „ Reports loud ; startled pheasants in a 



cover close by. 

 Tuddenham. St. Martin 10 ,, Reports very loud ; rolled away like 



thunder. 

 Christ Chvirch Park ... 11 „ Report arrived a little more than a 



minute after flash. 

 Nettlestead Hall 6 ,, Distinct in every part of observer's 



house. Very loud in the open air. 

 Bildestone 6 ,, Explosion very loud, wind against 



sound. 

 Nacton 14 ,, Reports quite distinct — mistaken by 



inhabitants for claps of thunder. 

 Aldboro 25 ,, Rockets seen through a very hazy 



atmosphere ; a rumbling detonation 



heard. 

 Capel Mills 11 ,, Reports heard within and without the 



observer's house. Wind opposed to 



sound. 

 Lawford isl ,, Reports distinct : attributed todistant 



thunder. 



It is needless to dwell for a moment on the advantage of pos- 

 sessing a signal commanding ranges such as these. 



The explosion of substances in the air, after having been carried 

 to a considerable elevation by rockets, is a familiar performance. 

 In 1873, moreover, the Board of Trade proposed a light -and- 

 sound rocket as a signal of distress, which proposal was subse- 

 quently realised, but in a form too elaborate and expensive for 

 practical use. The idea of the gun-cotton rocket with a view to 

 signalling in fogs is, I believe, wholly due to the Deputy Master 

 o( the Trinity House.^ Thanks to the skilful aid given by the 

 authorities of Woolwich, by Mr. Prentice, and Mr. Brock, that 

 idea is now an accomplished fact, a signal of great power, 

 handiness, and economy, being thus placed at the service of our 

 mariners. Not only may the rocket be applied in association 

 with lighthouses and lightships, but in the Navy also it may be 

 turned to important account. Soon after the loss of the Van- 

 guard I ventured to urge upon an eminent naval officer the 

 desirability of having an organised code of fog-signals for the 

 fleet. He shook his head doubtingly, and referred to the diffi- 

 cult of finding room for signal-guns. The gun-cotton rocket 

 completely surmounts this difficulty It is manipulated with ease 

 and rapidity, while its discharges maybe so grouped and combined 

 as to give a most important extension to the voice of the admiral 

 in command. 



I have referred more than once to the train of echoes which 

 accompanied the explosion of gun cotton in free air, speaking of 

 them as similar in all respects to those which were described for 

 » I have proposed that it should be called the " ColUnson Rocket." 



the first time in my report on fog-signals, addressed to the Cor- 

 poration of Trinity House in 1874.^ To these echoes I attached 

 a fundamental significance. There was no visible reflecting 

 surface from which they could come. On some days, with hardly 

 a cloud in the air, and hardly a ripple on the sea, they reached 

 lis with magical intensity. As far as the sense of hearing could 

 judge, they came from the body of air in front of the great 

 trumpet which produced them. The trumpet-blasts were five 

 seconds in duration, but long before the blast had ceased the 

 echoes struck in, adding their strength to the primitive note of 

 the trumpet. After the blast had ended the echoes continued, 

 retreating further and further from the point of observation, 

 and finally dying away at great distances. The echoes were 

 perfectly continuous as long as the sea was clear of ships, 

 ' ' tapering " by imperceptible gradations to absolute silence. But 

 when a ship happened to throw itself athwart the course of the 

 sound, the echo from the broadside of the vessel was returned 

 as a shock which rudely interrupted the continuity of the dying 

 atmospheric music. 



The day on which our latest observations were made was par- 

 ticularly fine. Before reaching Dungeness the smoothness of the 

 sea and the serenity of the air caused me to test the echoing 

 power of the atmosphere. A single ship lay about half a mile 

 distant between us and the land. The result of the proposed 

 experiment was clearly foreseen. It was this. The rocket being 

 sent up, it exploded at a great height ; the echoes retreated in 

 their usual fashion, becoming less and less intense as the distance 

 of the surfaces of reflection from the observers increased. About 

 five seconds after the explosion, a single loud shock was sent 

 back to us from the side of the vessel lying between us and the 

 land. Obliterated for a moment by this more intense echo, the 

 aerial reverberation continued its retreat, dying away into 

 silence in two or three seconds afterwards. 



I have referred to the firing of an 8-oz. rocket from the deck 

 of the Galatea, on March 8, 1877, stating the duration of its 

 echoes to be seven seconds. Mr. Prentice, who was present at 

 the time, assured me that, in his experiments with rockets, 

 similar echoes had been frequently heard of more than twice 

 this duration. The ranges of his sounds alone would render 

 this result in the highest degree probable. 



There is not a feature connected with the aerial echoes which 

 cannot be brought out by experiments in the laboratory. I have 

 recently made the following experiment : — A rectangle 22 inches 

 by 12, is crossed by twenty-three brass tubes, each having a slit 

 along it from which gas can issue. In this way, twenty- three low, 

 flat flames are obtained. A sounding reed, fixed in a short tube, 

 is placed at one end of the rectangle, and a " sensitive flame " at 

 some distance beyond the other end. When the reed sounds, the 

 flame in front of it is violently agitated, and roars boisterously. 

 Turning on the gas, and lighting it as it issues from the slits, the 

 air above the flames becomes so heterogeneous that the sensitive 

 flame is instantly stilled by the aerial reflection, rising from a 

 height of 6 inches to a height ot 18 inches. Here we have the 

 acoustic opacity of the air in front of the South Foreland 

 strikingly imitated. Turning off the gas, and removing the sen- 

 sitive flame to some distance behind the reed, it burns there 

 tranquilly, though the reed may be sounding. Again lighting 

 the gas as it issues from the brass tubes, the sound reflected from 

 the heterogeneous air throws the sensitive flame into violent 

 agitation. Here we have imitated the aerial echoes heard when 

 standing behind the syren-trumpets at South Foreland. The 

 experiment is extremely simple and in the highest degree im- 

 presssive. 



THE IRON AND STEEL INSTITUTE 



'T'HE ninth annual meeting of the members of the Iron and 

 ■*■ Steel Institute was commenced on Thursday in the rooms 

 of the Institution of Civil Engineers in Westminster. The chair 

 was occupied by Dr. C. W. Siemens, F.R. S., the President of 

 the Institute, and the proceedings were commenced by the read- 

 ing of the Annual Report of the Council, which stated that the 

 total number of members now exceeds 900, while a steady 

 accession of new members continues, there being 47 proposed 

 for election at the present meeting. The Council referred to 

 the increase of foreign members, which shows the interest taken 

 in the institute by Continental and American metallurgists. An 

 invitation received from M. Tresca on behalf of the Societe des 

 Ingenieurs Civils, to visit Paris in the ensuing summer and the 

 concurrent holding of the International Exhibition in that city, 

 ' See also Philosophical Transactions for 1874, P- iSs- 



