3 62 



NA TURE 



[August 14, 1884 



age they weigh from eight to twelve pounds, and in the 

 fifth year from twelve to fifteen pounds. From that age 

 upwards the weight increases rapidly. 



The results of the artificial hatching in the Weser are 

 exceedingly promising. Thus the salmon fisheries at 

 Hameln have been doubled in consequence during the 

 last ten years, the tax at present paid to this town 

 alone by the salmon fisheries being more than a thousand 

 pounds. 



In Norway, too, efforts have been made in the same 

 direction during the last few years. Thus in 1883 the 

 Storthing granted a sum of money for this purpose, and 

 with this amount the Chief Inspector of Fisheries, Herr A. 

 Landmark, has effected the marking of several hundreds 

 of salmon and trout, chiefly on the west coast of Norway, 

 during last autumn and winter. The marking here is 

 effected by means of a tiny bit of platinum, 7 mm. long, 

 and 4 mm. broad, being thus about the size of the nail on 

 the little finger, which is attached by a very fine platinum 

 wire to the fat fin of the big fish and the tail of the smaller 

 ones. The piece has a number stamped on it, which cor- 

 responds with one in a " log " giving all the particulars 

 as to the date the fish was marked, its weight, size, &c. 



In order to encourage fishermen to be 011 the look-out 

 for these marked fish, the inspector offers a reward of two 

 shillings and sixpence for each mark forwarded to him, if 

 accompanied with precise information as to the spot and 

 date when it was taken, the length and breadth of the 

 fish, and its weight. 



As these researches will tend greatly to ascertain the 

 habits and migrations of Salmonidee, the result will be 

 watched with interest. 



THE TRINITY HOUSE EXPERIMENTS ON 

 LIGHTHOUSE ILLUMINANTS 



THE great advances made during the past few years 

 in the science of illumination have rendered it de- 

 sirable, or rather absolutely necessary, that experiments 

 should be undertaken with a view to the determination of 

 the advantages and disadvantages attending the use of 

 different illuminants in lighthouses. With this view the 

 Corporation of Trinity House have commenced a series 

 of experiments at the South Foreland. 



There are at present on the South Foreland two light- 

 houses, known as the high light and low light, and both 

 of these are illuminated by electricity. Near these, three 

 experimental lighthouses have been erected for use with 

 the electric light, with gas and with oil respectively. The 

 electric apparatus consists of three arc lamps and three 

 magneto-electric machines made by Baron de Meritens. 

 The lamps are placed one above the other in the tower. 

 The carbons being used are l; compound carbons," made 

 up of many small rods of carbon of square section, coated 

 with copper, and Siemens's " core-carbons," made of 

 gas-carbon, with a central rod of graphite. When worked 

 up to their full power, each lamp is estimated to be 

 capable of giving a light equal to 30,000 candles. 



The second tower is fitted up with Mr. Wigham's gas- 

 burners. To supply the burners a small gasworks, fitted 

 with retorts, purifiers, and a gasholder capable of holding 

 about 5000 cubic feet, have been erected near bv. The 

 tower contains four burners, one above the other, each 

 burner consisting of concentric rings of jets. The total 

 number of jets on each burner is 10S, making a total on 

 the four burners of 432 jets ; but the outer rings maybe 

 removed when less light is required : so that each burner 

 may be used with 28, 48, '>8, 88, or 108 jets. A talc chim- 

 ney above the flame produces the necessary draught ; no 

 glass or talc is placed over the most luminous portion of 

 the flame. 



The intensity of the light when all the jets on all four 

 burners are used is stated by the inventor to be equal t<> 



1 2,000 candles. The third tower is for the present devoted 

 to the oil and gas-burners invented by Sir James 

 Douglass. The oil is supplied from a tank to the burners 

 under a slight pressure. One oil-burner has six con- 

 centric wicks, and has a power of 720 candles ; a second 

 has seven wicks and a power of 1000 candles. There 

 are three burners in the tower, placed one above the 

 other. Each tower is provided with lenses both for 

 revolving and for fixed lights. The highest power of the 

 gas tower is a quadriform light, of the other towers a 

 triform light. Besides the illuminants already mentioned, 

 there are gas-burners from the Sugg and from the 

 Siemens Companies, which will be tested in the light- 

 house towers. 



For observing the lights and testing them, a line ot 



Local Map for Observ 



observation has been measured out in the direction of 

 Deal, and three huts have been erected at a distance of 

 \ mile, \\ mile, and i\ miles respectively from the 

 towers. These huts are fitted up as photometric observa- 

 tories. The lights are focussed on one of the huts, and 

 they are then measured in all conditions of weather by 

 means of the pentane unit of light devised by Mr. Vernon 

 Harcourt. When the weather is too thick' to allow of 

 direct comparison with the unit, the lights are compared 

 one with another by means of a polariscope-photometer, 

 in which the ordinary image of one light is brought to 

 equality by means of a Nicol prism with the extraordinary 

 image of another light. In ordinary weather a ray from 

 the lighthouse tower enters a hole in a shutter and falls 



