1920] The Gyrostatic Compass 19 



WEEKLY EVENING MEETING, 



Friday, January 30, 1920. 



Sir James Crichtox-Browne, J.P. M.D. LL.D. F.R.s.. 



Treasurer and Vice-President, in the Chair. 



Sidney G. Brown, F.R.S. M.I.E.E. M.R.I. 



The Gyrostatic Compass. 



This lecture is on the Gyrostatic Compass, called in short the Gyro- 

 Coinpas>. 



An engineer of my acquaintance was asked if he understood what 

 a Gyro-Compass was, and he replied, " Of course I do ; it is a magnetic 

 compass mounted upon a gyroscope." 



Xow that is not correct, because the Gyro-Compass has nothing 

 to do with magnetism or the magnetic compass. The only thing 

 that these two instruments have in common is to point towards the 

 north and south poles of the earth. 



I am, therefore, anxious that this should be clearly understood, 

 because in a recent lecture I gave at Bournemouth on this very 

 subject, one of the audience asked me after the lecture how I 

 shielded the Gyro-Compass from outside magnetic influence. I 

 pointed out to him, as I had endeavoured to do during the lecture, 

 that the Gyro-Compass had nothing to do with magnetism, and, 

 therefore, did not require shielding. He then asked me what worked 

 the compass. I said it received its directive action from the rotation 

 of the earth ; this I fear was too much, for after looking at me re- 

 proachfully he moved away. 



I, therefore, want you to get firmly fixed in your minds, that the 

 magnetic compass and the Gyro-Compass are two absolutely different 

 instruments operated by entirely different laws, although they are for 

 the same purpose. 



I have often been asked why a Gyro-Compass is needed when 

 the magnetic compass is already available, and I therefore feel it 

 necessary to say a few words on the magnetic or mariner's compass 

 before attempting to explain the Gyro-Compass. 



The mariner's compass consists of a magnetic needle, or of several 

 magnetic needles fixed side by side, and balanced upon a sharp point. 



A card divided into 32 (points of the compass) is attached to the 

 needle, and swings round with it, so that the point marked X on the 

 card alwavs points to the north. 



C 1' 



