EVENING DISCOURSES. 421 



aiid the curve drawn during the lecture by one of the repeaters showed how very 

 effective the damping is. 



The gyro case and bottle system is supported on knife edges (on the level of 

 the centre of gravity) on a vertical ring which is supported below on a friction- 

 less mounting (the oil pump), and above carries the compass card. The whole is 

 carried on gymbals and an outer row of springs to take up shock. 



A second air jet is employed to work the repeaters. It acts upon a pair of 

 contact-making vanes, and these contacts, through the agency of ' the controller ' 

 which is fixed on the switchboard, work the repeaters and a step-by-step motor 

 which forces round a follow-up ring to keep the contact-making vanes always 

 opposite the air jet. When the compass is fixed to a rolling table which imitates 

 the rolling of a ship it is interesting to see that the motion of the oil in the larcrer 

 bottles 16 a quarter period behind the roll, whereas the pendulous motion 

 synchronises with the roll. This is the reason why there is no quadrantal error 



The idea of a gyro-compass is old, but Anschiitz deserves great credit for 

 first carrying out the idea. He knew that the directive action of tRe earth 

 was exceedingly feeble, and he had amazing courage in placing the instrument on 

 a rolling, pitching, plunging ship. One of the Brown compaeses on a flagship 

 in stormy weather in the North Sea about a year ago was subjected to particularly 

 accurate observation, and it was found never to depart more than one degree 

 from the true direction. 



The reader of this abstract is under the disadvantage that he cannot see 

 the experiments or lantern slides, or the whole compass or its parts, and at two 

 places short explanations by the abstractor have been given instead of the longer 

 popular illustrated explanations of the lecturer. 



1919. ^ J 



