September i, 1892] 



NA TURE 



431 



be a chamber to which the sea would have access, and in this 

 would be a diaphragm which would be tuned to the same note 

 as that emitted by the siren. By the well-known law the 

 diaphragm would not resound unless the note to which it might 

 be attuued were in harmony with that given off by the siren, 

 and therefore false alarms would not be given by the sounds 

 produced by paddle wheels or in other ways. An officer would 

 be placed in a padded cabin, so as to isolate him from the noises 

 of the ship, and by means of an ordinary speaking-tube he 

 would be able to hear the vibrations of the diaphragm, 

 which, as stated, would only take place when they syn- 

 chronised with the sound-waves produced by the siren. Mr. 

 Sennett's proposal is ingenious, and may contain the germ of a 

 principle of great value. We understood him to say that he 

 had made some experiments in this direction, and that these had 

 been encouraging. It is obvious, however, that investigations 

 of this nature must be somewhat costly, and can lead to but 

 little prospect of pecuniary reward. We would suggest that 

 the matter is one that might well be taken up by the Board of 

 Trade or the Trinity House. Perhaps some of those big ship- 

 owners who do their own insurance might be induced to give 

 assistance in this direction. It is quite possible, and indeed 

 probable, that we have been entirely on the wrong tack in 

 sending sound-signals through the air. The experience of Prof. 

 Hughes, quoted by Mr. Sennett, when he found the sound of 

 two stones being knocked together under water could be heard 

 for a distance of half a mile, and heard so distinctly that the 

 Professor did not wish to repeat the experiment, bears on this 

 point. An ordinary bell has been struck under water, and the 

 sound conveyed a distance of nine miles. 



Mr. C. A. Stevenson next read a paper of his own " On the 

 Progress of the Dioptric Lens as used in Lighthouse Illumina- 

 tion." This paper was largely historical, going back to the 

 early days of the century, when Alan Stevenson introduced the 

 Fresnel apparatus in Great Britain, and bringing the record up to 

 the year 1886, when the author proposed the spherical lens, an 

 example of which was introduced in one of the Fair Isle light- 

 houses. This introduction of the spherical refractor has made 

 practicable the construction of more powerful apparatus, with 

 less total space occupied. It has also rendered practicable a 

 quadrilateral arrangement with hyper-radiant lenses. This 

 arrangement has been installed at Fair Isle, the lenses being cut 

 so as to give two flashes from each side of the quadrilateral. 

 An experimental example for Ireland is 2 m. focal distance, and 

 the spherical refractor is 7' 6" in diameter, and will give one 

 flash from each side of the quadrilateral. 



Mr. A. R. Sennett next read a paper which was both interest- 

 ing and of practical importance. Its theme was the much ill- 

 treated smoke-prevention question, and we may at once say it 

 was refreshing to find this important but ever-abused problem 

 approached in an intelligent manner. Mr. Sennett has evolved 

 a very simple device which, it might perhaps be rash to say, has 

 exorcised the smoke fiend in regard to boiler furnaces ; but if we 

 are to accept his statements — and we see no reason why we 

 should not — there is no longer excuse for steam users allowing 

 smoke to emerge from boiler chimneys. We all know it is not 

 difficult to prevent smoke if fuel economy be left out of the 

 question, but Mr. Sennett tells us he not only prevents smoke, 

 but saves coal. The latter part of the claim is vouched for by 

 Professor Alexander Kennedy, who is perhaps our best authority 

 on this subject ; and, with regard to the smoke prevention. 

 Section G was able to judge for itself, as the author had a (air- 

 sized return-tube boiler at work in a yard close to the meeting- 

 room. The paper was of considerable length, but was listened 

 to with interest throughout. By means of wall diagrams, de- 

 vices of various classes, previously introduced, were illustrated 

 and described. These played much the same part as the awful 

 example at a teetotal lecture, only serving to emphasize the 

 virtues of the author's own invention. Some of them, it must 

 be confessed, were sufficiently absurd ; one especially, in which 

 the products of combustion were cleansed from soot by a sand 

 filter, afforded the meeting a good deal of amusement. We 

 imagine the impression of the average engineer to be that the 

 drier and hotter the air fed to a furnace the quicker and more 

 perfect would be the combustion. This Mr. Sennett shows 

 to be not exactly the fact, or, at any rate, that the presence 

 of steam with the air promotes combustion. He says that 

 hydrogen, steam, or aqueous vapour, in the furnace is necessary. 

 He combats the view, " too readily assumed," that the presence 

 of an excess of oxygen contained in dry air will of necessity 



NO. 1 192, VOL. 46] 



effect complete combustion. The advantage of supplying air 

 above the grate bars, as well as below, is, of course, 

 well understood, and it is with the volume of air intro- 

 duced above that the author chie ly deals. His device 

 consists chiefly of an air injector, the steam for inducing 

 the air-current being super-heated in a coil placed 

 in the chimney. The apparatus is termed a transformer, 

 because it transforms the kinetic energy of a small current of 

 steam at high pressure into that of a large current of air at low 

 pressure : a description which conveys the whole scheme of the 

 invention, although the working out of the details requires some 

 attention. With the transformer Mr. Sennett has carried out 

 some experiments. He worked it firstly by steam, and secondly 

 by compressed air, and he found that the volume of air required 

 for combustion was very much less in the former case than in 

 the latter. In explanation, or rather in illustration, of this fact 

 the author quotes several interesting facts. Mr. H. Brereton 

 Baker investigated the phenomena which accompany the burn- 

 ing of carbon and phosphorus in oxygen. Finely powdered 

 charcoal was carefully dried and sealed up in a hard glass 

 tube containing oxygen saturated wiih water. The tubes were 

 placed in a flame, and the carbon burnt with brijht scintillating 

 flashes. When the oxygen was dry no combustion took 

 place in the tube, though the latter was heated to bright red ; a 

 result which came clearly as a surprise to many of the members 

 of non-chemical Section G. Mr. Baker has said that the results 

 obtained clearly show that the burning of carbon is much 

 retarded by drying the oxygen. With regard to the presence of 

 moisture and the behaviour of carbonic oxide gas in oxygen the 

 effect is even more remarkable. The author quotes Prof. H. 

 B. Dixon, who says : " That if the mixture of the two gases be 

 very carefully dried it is no longer explosive, and a platinum 

 wire may be heated to redness in it without causing explosion ; 

 oxidation of the carbon monoxide to dioxide then taking place 

 gradually, and only in the immediate neighbourhood (at the 

 surface) of the glowing wire. A burning jet of carbonic oxide 

 may even be extinguished by plunging it into a jar containing 

 dried oxygen." We will quote one more interesting fact in 

 I connection with this subject. Sir Lowthian Bell has noticed 

 I that the gases at the throat of blast furnaces, which are of a 

 temperature of about 250 to 300 Cent., are not inflammable 

 I in atmospheric air. Any small quantity which escapes does so 

 I without undergoing combustion. But the moment a tuyere com- 

 mences to leak the gas takes fire ; just as a small quantity of 

 hydrogen in the eudiometric researches produced explosion in a 

 mixture not previously influenced by the electric spark. The 

 author does not attempt to decide whether the acceleration or 

 retardation of the union of oxygen with the evolved hydro-carbon 

 gases is due to the presence of aqueous vapour or of the 

 hydrogen. Section G may fairly look to Sections A or B for 

 enlightenment upon that point. 



We have given so much space to what we think the most inter- 

 esting part of Mr. Sennett's paper that we may, perhaps, be doing 

 him the injustice of suggesting that other points do not receive 

 attention. This, however, is not the case, for he does not lose 

 sight of the leading canons of furnace practice, such as proper 

 admixture of the gases, adequate space for combustion, keeping 

 the gases from contact with the heating surface (from this point 

 of view the cooling surface) of the boiler, and other matters, 

 of a similar nature. The result of the whole arrangement is that 

 smoke is undoubtedly prevented from issuing from the funnel. 

 In the boiler referred to a very dirty coai was burned, the 

 result being a particularly pungent smoke, which was sometimes 

 carried down among the spectators by an eddying wind. When 

 the transformer was put in operation this smoke entirely disap- 

 peared. Upon the apparatus being put out of action the sable 

 cloud was again to be seen rolling forth from the chimney-top. 

 These operations were repeated several times, the fire being 

 constantly supplied with green fuel, so as to keep it in its 

 smokiest condition. 



Following Mr. Sennett's paper a contribution on the same 

 subject was read by Colonel E. Duller. The author of this 

 paper deals with the domestic fire, to which, of course, the 

 greater part of the smoke of civilization is to be attributed, but he 

 does not aim at the prevention of smoke, but simply to itsarresta- 

 tion before its gets into the air. In order to effect this object 

 he proposes to wash the chimney gases with a spray, and thus 

 precipitate all soot. He also claims to arrest the greater part 

 of the sulphurous acid, which is of even greater importance. 

 Every dweller in towns and cities will wish Colonel Duller well 



