CHAPTER IX 



GYROSCOPIC COMPASS METHODS OF SURVEYING 



BOREHOLES 



Introductory Note. — The gyroscope being uninfluenced 

 by local attraction is well suited to the survey of boreholes. 

 The physicist, Foucault, whose pendulum researches are 

 well known, instituted in the middle of last century the law 

 that a spinning wheel with three directions of freedom, i.e., 

 one which is free to move in all three dimensions, is unin- 

 fluenced by the force of gravity and 

 is suited to indicate the rotation of 

 the earth. In order to have a freely 

 moving wheel it must have Cardan 

 suspension. In order that the action 

 of gravitation be removed the three 

 axes must all meet in the center of 

 gravity of the system (Fig. 143). 

 Such a gyroscope is called an azimuth 

 gyroscope and then if no external 

 force acts on it — whether at rest or 

 rotating — it keeps its position in 

 space unchanged. The term ''azi- 

 muth gyroscope" is not happily 

 chosen because the magnetic compass 

 also has an azimuth, only this is not optional but zero 

 (meridian) . 



Foucault has also shown that a gyroscope which is com- 

 pelled to move in a horizontal plane endeavors to adjust 

 itself to the north-south line. Such an arrangement is 

 called a gyroscopic compass or gyrocompass. In England 

 and France experiments have been undertaken since well 

 into last century, with the purpose of utilizing the gyroscope 

 as a compass. In Germany experiments have been under- 



204 



Fig, 



14 3 . — Wheatstone's 

 gyroscope. 



