30 



Mr. Sidney G. Brown 



[Jan. 30, 



The force with which the compass seeks the north is proportional 

 to the product of the rotation Tone revolution in 24 hours) and the 

 spin of the wheel. The faster we can spin the wheel the more do 

 we obtain directive force. It is for this reason that the wheel is 

 ed at its maximum speed and strength consistent with the rise 

 of temperature. 



Taking the "Brown" Gyro-Compass as an example, the wheel, 

 which is I in. in diameter and 4J lbs. in weight, runs at 15,000 

 revolutions per minute. The maximum directive force of the earth 

 on this wheel — that is, when the spindle is pointing east to west — is 

 only the weight of 30 grains, with a leverage of 1 inch. 



Fig. 6. — Speery Gyro-Compass. 



This small force is continually diminishing in value as the axis 

 approaches the north direction, and vanishes absolutely in that 

 position. 



If the compass were deflected, say 1' from the north, then the 

 force of restoration is only h grain at a leverage of 1 inch. It will 

 therefore he seen how important it is to eliminate as completely as 

 possible any friction on the vertical axis that would tend to oppose 

 the directive action of the earth. 



There are three forms of Gyro-Compass now in use, the Anschutz 

 man), the Sperry (American), and the ' ; Brown " (British). 



In the " Anschutz, "' Fig. 4, the vertical axis is supported by a 



