June 30, iyi^7] 



NA TURE 



203 



l^et achieved by gas, oil, or electricity, and visible not 

 iPonly on the horizon, but across half the midnight sky. 

 ' Phonic signals as auxiliary to luminous signals have 

 engaged the attention of our lighthouse authorities from 

 dates previous to 1837, aird almost continuously from 

 1848 to 1875. The early instruments were the bell, the 



Sgun, and the gong, with sometimes an explosive such as 

 a rocket. Between 1848 and 1850, Mr. G. Wells pro- 

 duced his patent "fog screamer" (by atmospheric pres- 

 sure), which, however, did not meet the approval of the 

 Trinity House, who, in 1853, considered that a good- 

 sized bell struck sharply by machinery surpassed any 

 mode yet tried. During the next ten years experiments 

 on fog-signals were carried on in France, and in 1864 

 there was an important investigation by the Government 

 of the United States. In 1872 a Committee of the Trinity 

 House visited that country and Canada, and tested the 

 merits of the new sound instruments in use, chiefly the 

 Daboll horn actuated by air, and the siren actuated by 

 steam. The Canadian and American steam-whistles and 

 the New York siren, together with air-whistles, air- 

 trumpets, and some guns, were next employed in the most 

 complete scientific and practical inquiry ever held into the 

 laws that regulate the passage of sound through the 

 atmosphere, and into the mechanical agents most suitable 

 to be adopted. The experiments were conducted by the 

 Trinity House at the South Foreland in 1873-74, under 

 the superintendence of Dr. Tyndall, who was able to 

 demonstrate that fog or heavy rain is permeable by sound 

 to a degree never before understood, and that optical 

 transparency might be combined, even as cause and 

 effect, with acoustical opacity or turbidity, and vice versa. 

 These results attracted much attention, and although 

 Prof. Tyndall's inductions as to homogeneity or non- 

 homogeneity of the atmosphere have been to some extent 

 questioned, the large body of facts on which they rest 

 has been still further enlarged and confirmed. It follows 

 that a fog dense enough to quench all light may permit 

 sound to be transmitted with unimpaired distinctness ; 

 and where the sound, either by alternations of pitch or of 

 interval, is made a substitute for the characteristics of a 

 light-signal, a very valuable secondary set of signals is 

 realized. Of the instruments tried at the South Foreland 

 the siren was found to be the most effective in almost all 

 circumstances. This instrument was the work of Mr. 

 Brown, of New York, to whom a simple and powerful 

 form of caloric engine is also due. It consists of a trumpet 

 about 17 feet long, increasing from 5 to 27 inches in dia- 

 meter, having two disks in it, one fixed and one rotating, 

 ■with radial slits in them. The rotation is from 2000 to 

 2500 times in a minute, steam at from 70 to 80 lbs. pres- 

 sure bei ng supplied. A note of varying pitch and intensity, 

 audible at distances from 3 to 10 miles is thus generated. 

 The siren in another form was improved by Dove and by 

 Helmholtz, and previously by Cagniard de la Tour, who 

 gave it this name, presumably on the hictis a non lucendo 

 principle It is now employed at many first-class land 

 lighthouses where space exists for the needful stqam or 

 caloric motor. Truly for the help not the harm of the 

 mariner, in the words of the poet, " Siren (issuctos effudit 

 in aquorc cantus.'' It is possible that the recent disaster 

 off Dieppe might have been averted if the Victoria, 

 moving doubtfully through the fog, could have heard the 

 steam-trumpet on Cap d'Ailly, which seems to have been 

 disabled at the critical time.' Both the range of the siren 

 and the facilities for working it have of late been enhanced 

 by the methods of Mr. Charles Ingrey, who, by employing 

 air compressed by engines of 40 horse- power, the air- 

 pressure being 80 lbs. per square inch, has, in the case of 

 the Ailsa Craig establishment, produced from two sirens 

 a sound audible, it is said, at a distance of 20 miles in 

 calm weather. One of these instruments gives single 

 blasts of 5 seconds duration, the other a high, low, and 

 high note in series, each of 2 seconds, with intervals of 



2 seconds between them, followed by 170 seconds of 

 silence. This is the phonic analogue of a single-flashing 

 and of a group-flashing light respectively. The com- 

 pressed air is conveyed from a considerable distance to 

 the siren-house, and Mr. Ingrey is confident that he could 

 work the instrument from an engine placed 10 miles 

 away. After the South Foreland experiments of 1874, 

 the Trinity House proceeded to improve the gun as a 

 sound-signalling agent. It now ranks as second to the 

 siren alone. Gun-cotton is proved to be a more effective 

 charge than powder, and it has been supplied with the 

 gun to a few lightships ; but the siren is for principal 

 stations, and the gong, or bell, or an explosive mixture, 

 for others. 



The details so far given, though necessarily incomplete, 

 illustrate the notable progress in lighthouse design and 

 construction attained in this country since the accession 

 of our Queen, and not less do they show the increasing 

 number of the lights established on our shores. . Along 

 with France and the United States — and due honour 

 must be accorded to the eminent men representing them 

 — Great Britain has proceeded steadily in the path of 

 investigation and experiment. And here the labours of 

 the celebrated Royal Commission of 1859-60 on lights, 

 buoys, and beacons should not be overlooked. This 

 Commission collected from all maritime countries and 

 from the leading authorities in official life, in engineering 

 and nautical science, in mathematics and physics, a vast 

 body of evidence which to the careful student will not 

 prove the riidis iiidigestaque moles it at first sight 

 appears. Some of the recommendations of the Com- 

 mission have been fully carried into effect during the last 

 quarter of a century, e.g. the proper adjustment of optical 

 agents to the flame and to the sea horizon, the develop- 

 ment of lamps and burners, the provision of reflectors, 

 testing of foci, &c. The conclusions also of the Com- 

 missioners on the complicated and anomalous system of 

 lighthouse government formulated by the Merchant Ship- 

 ping Act of 1S54 have never been impugned ; and the 

 expediency of a central Lighthouse Board as suggested 

 by them, and as indeed had been suggested by the Par- 

 liamentary Committee of 1834, has become more and 

 more evident down to the present day. 



But while Great Britain has, in common with France 

 and the United States, pursued this path of inquiry and 

 reform, she has distanced these countries altogether in 

 the results of research and the realisation of improvement. 

 The splendid gift of the dioptric system was made to the 

 world by the genius of Fresnel, yet little has been added 

 to it by his countrymen. The most solid and important 

 additions and applications are the work of Scottish and 

 English engineers, whether in the optics or the mechanics 

 of lighthouses, whether in oil, gas, or electricity. And 

 the gift of Fresnel has thus been returned enhanced three- 

 fold to France and to the world. How it has been 

 i-eceived is apparent by this one indication : the yearly 

 statistics of our Admiralty comprise forty lighthouse 

 notices issued to mariners in 1862, and 311 issued in 

 1886, the subjects of these notices being mainly new 

 lights, and the new lights being mainly on the most 

 modern lenticular system. 



Note. — Since the above was written the small circle of 

 men associated with lighthouse illumination has been 

 broken by the death of its most distinguished member, 

 Thomas Stevenson, who, during the whole of the half 

 century under review, did more than any other to multiply 

 for engineers the resources of his science, and to diminish 

 for all the world the manifold perils of the sea. 



The extraordinary power of the electric light has been 

 referred to in connexion with the apparatus of I sola del 

 Tino. In a recent communication to the Siandard from 

 " C P. S." from Via Reggio, further testimony is given to 

 this power in clear weather, but a far more important and 



