44 



NATURE 



TMarch II, 1920 



The Marine r's Compass. 



M 



ORE than 300 years ago William Barlow, ; 

 writing of the compasses of his day, said j 

 that, though the compass needle was "the most 

 admirable and useful instrument of the whole 

 world," yet nothing was more "bungerly and 

 absurdly contrived." How little advance was 

 made in the succeeding two centuries can be 

 gathered from Peter Barlow's remark to the Lords 

 of the Admiralty in 1820 that "the compasses in 

 the British Navy were mere lumber, and ought to 

 be destroyed." It was Barlow himself who made 

 the Hrst notable improvements in compasses during 

 the nineteenth century, and his work was the 

 prelude to the important investigations of Airy, 

 Archibald Smith, Kelvin, and others. The prac- 

 tice of " swinging ship "—that is, turning a ship 

 slowly round and noting the deviations of the 

 compass in different positions by taken bearings- 

 was introduced in 1810 by Matthew Flinders, who 

 also invented the use of the " FHnders bar," a rod 

 of soft iron placed near the compass to correct 

 for changes in the magnetism of the ship due to 

 the vertical component of the earth's magnetism. 



The gradual increase in the employment of 

 wrought-iron fittings in wooden ships; the use of 

 iron cables instead of hempen ; the placing aboard 

 of ponderous iron boilers and engines; and, lastly, 

 the construction of the vessel itself of iron, each 

 in its turn added difficulties to the problems 

 involved. Barlow, in his attempts in 18.19 to find 

 a remedy for the large deviation due to the extend- 

 ing use of iron in ships, made the first experi- 

 mental investigation of the phenomena of induced 

 magnetism. From his inquiry he was able to give 

 a simple means of correcting ships' compasses by 

 fixing soft iron discs in suitable places near the 

 compass, and he afterwards introduced a type of 

 compass having four or five parallel straight strips 

 of magnetised steel fixed under a card, which 

 remained the standard pattern until Kelvin brought 

 out his famous patent in 1876. 



The mathematical investigations of Poisson an' 

 of Airy about 1838 led to the introduction of 

 methods of correction by the use of permanent 

 magnets, and also of the well-known soft iron 

 spheres. Many of Airy's experiments were made 

 In the iron vessel Rainbow off the old Woolwich 

 Dockyard. 



The story of Kelvin's share in the improvement 

 of the compass has often been told. Asked in 1871, 

 by his friend Norman Macleod, to write an article 



for the newly founded magazine, Good Words, 

 Kelvin chose as a topic the mariner's compass. 

 The first part of his article appeared in 1874,^ and 

 the second not until five years later. "When 1 

 tried," he said, "to write on the mariner's com- 

 pass, I found I did not know nearly enough about 

 it. So I had to learn my subject. I have been 

 learning it these five years." The Admiralty 

 standard compass, adopted in 1842, and in use 

 when Kelvin took up the matter, had a card 7^ in. 

 in diameter, and under it four needles, each of 

 which was a long, straight bar of flat clock spring 

 placed on edge. The card and the needles weighed 

 about 1600 grains, and had a period of vibration 

 of 19 sec. So considerable was the friction 

 that the binnacle was often kicked by the sailors 

 to make the card move. Kelvin's "gossamer 

 structure " of eight small needles weighed about 

 170 grains, and had a period of about 40 sec. 

 The cold reception Kelvin received from the then 

 Hydrographer to the Navy, and Airy's remark 

 on the compass, "It won't do," remind one of the 

 reply made to Berthon in 1835 : "The screw was 

 a pretty toy which never would and never could 

 propel a ship." 



The ultimate adoption of the Kelvin compass 

 was largely due to Lord Fisher, who had one on 

 board the Inflexible at the bombardment of Alex- 

 andria in 1882. Torpedo craft, however, continued 

 to be supplied with a form of compass in which 

 'the whole card floats in liquid, and improvements 

 made in this type led to its being adopted as 

 the standard compass about 1906. Since this has 

 come the invention of, first, the Anschutz, then the 

 Sperry, and, now, the Brown gyro-compasses, the 

 introduction of which has taken place during the 

 last ten years. As remarked by Mr. S. G. Brown 

 in the Royal Institution discourse reproduced below, 

 the gyro-compass is a necessity in a submarine, 

 while in largef vessels it has the great advantages 

 that it can be placed below the water-line more 

 or less immune from gunfire, and lends itself to 

 utilisation with fire-control apparatus and the tor- 

 pedo director. 



All the work on compasses for the Navy is 

 to-day carried out at the new Admiralty compass 

 observatory at Ditton Park, near Slough, where 

 the work of the five departments — the gyro- 

 compass branch, magnetic compass branch, optical 

 branch, experimental branch, and air cQmpass 

 branch — is superintended by the director, Capt. 

 F. O. Crcagh-Osborne. 



The Gyrostatic Compass. 



By S. G. Brown, F.R.S.^ 



The subject of this lecture is the gyrostatic 

 •compass, often called the gyro-compass. An 

 •engineer of my acquaintance was asked if he under- 



l Discourse delivered at the Royal Institution on Friday, January 30. 



NO. 2628, VOL. 105] 



stood what a gvro-compass was, and he replied, " Of 

 course I do; it is a magnetic compass mounted upon 

 a gyroscope." Now the gyro-compass has nothing 

 to do with magnetism or the magnetic compass. The 



