April 22, 1886] 



NA TURE 



589 



changes as the ship moves into fresh magnetic latitudes. 

 c c are soft iron rods, intended to represent iron masts. 



Quadrantal deviation of the form generally observed is 

 produced by the soft iron rod e , extending from side to 

 side under the deck D D' like a deck beam, the rods a a 

 also conspiring with c in increasing the quadrantal de- 

 viation. That part of the heeling error caused by the 

 magnetism of the hard iron of a ship is produced by a 

 small vertical magnet in the position of the rod / when 

 removed ; that from soft iron by the vertical soft iron 

 rod k and the horizontal I'od e'. 



The compass C having been disturbed by magnetic 

 forces of the usual type in an iron ship, may now be 

 corrected: m" ti" \s a magnet with its north or marked 

 end, n", towards the stern of the model, and near enough 

 to the compass to correct the deviation on the east and 

 west points : ni' it is a second magnet with its north or 

 marked end, n', towards the port side, correcting the de- 

 viation on the north and south points. Or the whole 

 semicircular deviation may be corrected by one magnet, 

 111 11, placed exactly in the direction of K, n being the 

 marked or north end. The quadrantal deviation is cor- 

 rected by the rods e e. The heeling error caused by e is 

 also nearly corrected by ee, and that caused by the sum 

 of the effects oi k and the vertical magnet under the com- 

 pass by another vertical magnet with the opposite pole 

 uppermost. 



Thus it will be seen that any component part of the 

 whole deviation usually found at the standard compass of 

 an iron ship may be produced in the model and the cor- 

 responding corrector provided. 



The portable model adopted by the Board of Trade 

 has a compass mounted on a ship's deck, as in the figure ; 

 but the deck, which rests on a central metal support, 

 revolves round a pivot in the centre of a fixed board, an 

 arrangement for inclining the model being provided. 



The disturbing magnets and soft iron are arranged 

 thus. For producing the semicircular deviation due to 

 the hard iron of a ship thin magnets are placed as re- 

 quired in any of the grooves cut in the deck radiating 

 from the centre of the compass, so that deviations due to 

 any direction of the ship's head whilst building may be 

 produced. For that part of the semicircular deviation 

 due to soft iron a vertical soft iron bar is fixed in the 

 central longitudinal line of the deck and near the stern. 

 For the quadrantal deviation hollow cylinders of soft iron 

 are placed under the deck similar to the rod e of the 

 figure. For the heeling error due to hard iron a magnet 

 is placed vertically under the compass. 



The correctors are magnets placed on the deck as in'n', 

 in"n" in the figure, and soft iron spheres — on brass 

 brackets which may be turned in azimuth round the com- 

 pass — instead of the rods e e ; z. Flinder's or vertical soft 

 iron bar before the compass ; a vertical magnet under 

 the centre of the compass to correct the heeling error. 



This model is exceedingly well adapted for instruction 

 and examination in the causes of the deviations generally 

 found at standard compass positions in the mercantile 

 navy, and the method of correction adopted in that 

 service. 



There remains now only the model made for the 

 Bureau of Navigation of the United States Navy Depart- 

 ment to be noticed. It consists of a miniature vessel of 

 which the stem, keel, and stern-post are of bronze cast in 

 one piece, with three wooden decks supported by bronze 

 screws. This model, called the Scoresby, is pivoted at 

 the stern by a socket in the floor, with a bronze wheel 

 fitted under the bow, so as to be easily turned round in 

 azimuth. The disturbing magnetic forces are produced 

 by magnets and hollow wrought-iron tubes of soft iron, 

 whilst wrought-iron plates can be attached to the sides of 

 the vessel. 



The Scoresby was designed with the object of 

 proving by experiment the mathematical theory already 



noticed. Experiments were consequently made as to the 

 effects of hammering the plates of the model with the bow 

 in different directions, a magnetic survey being made 

 after the hammering to determine the polarity in different 

 sections, and its degree of permanency or otherwise. The 

 model was next swung both when upright and inclined, 

 for the deviations of the compass produced by a magnet 

 or soft iron tube representing each parameter singly, com- 

 binations being made afterwards as desired. These 

 experimental results proved satisfactorily the correctness 

 of the mathematical theory. 



This general description of the Scoresby will serve 

 to show that the Americans have taken considerable 

 pains in making valuable experiments in proof of theory, 

 and for instruction to the seaman. Before parting with 

 her, however, a quotation from the American profes- 

 sional paper on the subject of the Scoresby seems 

 worthy of a place, as sounding a fresh warning note to 

 those who ruthlessly distribute iron ad libitum and in any 

 form round the position of a ship's standard or guiding 

 compass. 



" Compensation of large deviations by means of mag- 

 nets is at the best but a remedy for an ailment ; better not 

 sow the seeds of the disease." 



The three models just described have been selected as 

 being the most modern specimens of these useful aids to 

 knowledge, but there are others for the instruction of offi- 

 cers in the Royal Navy which have been in use for some 

 years past. It will be gratifying to the many who take 

 interest in maritime affairs to note the increasing anxiety 

 for the spread of a sound knowledge of the principles of 

 the magnetism of iron ships and the deviations of their 

 compasses which the construction of these models 

 manifests. 



NOTES 

 The total number of candidates for election into the Royal 

 Society this jear is sixty-two. Of these the following fifteen 

 have been selected by the Council to be recommended to the 

 Society for election ; the voting will take place on June 4 : — 

 Shelford Bidwell, M.A., W. Colenso, F.L.S., H. B. Dixon, 

 F.C.S., E. R. Festing, Major-Gen. R.E., Prof .\. R. Forsyth, 

 M.A., Prof. A. H. Green, M.A., Prof. Victor Horsley, 

 F.R.C.S., T. R. Lewis, M.B., R. Meldola, F.R.A.S., P. H. 

 Pye-Smith, M.D., H. C. Russell, B.A., Prof W. C. Unwin, 

 B.Sc, R. Warington, F.C.S., Capt. W. J. L. Wharton, 

 F.R.A.S., and H. Wilde. 



The following are the probable arrangements for the Friday 

 evening meetings of the Royal Institution after Easter : — 

 May 7, Mr. Frederick Siemens, "Dissociation"; May 14, 

 Prof John Millar Thomson, F.C.S., "Suspended Crystallisa- 

 tion"; May 21, Sir John Lubbock, Bart., M.P., F.R.S., 

 "The Forms of Seedlings : the Causes to which they are due " ; 

 May 2S, Prof Oliver Lodge, D.Sc, "Electrical Deposition of 

 Dust and Smoke" ; June 4, WaUer H. Gaskell, M.D., F.R.S., 

 "The Sympathetic Nervous System" ; June 11, Prof Dewar, 

 M.A., F.R.S. 



The e.d:\l.oxoi'Ca^ Sidereal Messenger (U.S.) writes in his April 

 number :—" We are glad to learn from private advices that a small 

 observatory will soon be fitted up with the necessary instruments 

 for continuous solar and local magnetic observation, in which 

 daily solar photographs of the sun will form an important part 

 of the work done by the observers. We are not aware that work 

 of this kind is now anywhere systematically undertaken in the 

 United States." 



The Congress of French Societes Savantes will take place as 

 usual at the Sorbonne, and the final ceremony under the chairman- 

 ship of M. Goblet, the present Minister of Public Instruction. It is 



