476 TRANSACTIONS OP SECTION G. 



The repeated running of the heavily laden tramcar wheel over the rail does 

 thus gradually compress the surface of the crown of the rail. Of this stress 

 transversely the material relieves itself partially by the detrusion at the edges 

 of the rail, where it forms a lip on the outeide or on the groove side, or on both. 

 This lip remains on the outside of the rail, but is worn off on the inside by 

 the wheel flange. In the longitudinal direction the stresses arising from the 

 compression of the surface material are not thus relieved. Areas of maximum 

 compression are thus originated round points separated by distances which are 

 determined mainly by the relation between compression resistance and elastic 

 tensile strength of the material rolled, but in part by the relative hardness of 

 the roller and rail and by the mechanical conditions which affect the area of the 

 rail and roll contact. The heavily laden tramcar wheel presses into the surface of 

 the rail, and as it rolls along presses before it a wave of compression the trans- 

 lation of which involves the destructive rupture of the surface or the rise of the 

 wheel over the minute crest of the wave. The result is the formation of an ex- 

 tremely hard surface in patches of various shapes and lengths, and separated by 

 distances depending on several conditions, including the mechanical properties 

 of the rail, its combined hardness and toughness. Where the bright hard 

 patches alternate with an approach to regularity with the dull and rougher 

 surface patches the result is known as corrugation. This character of sur- 

 face may be found on every heavily worked tramway under conditions of such 

 impartial contrariety that it may be ascribed to conditions of origin which are 

 general. 



The remedy appears to be: (1) lighter cars; (2) larger wheels; (3) harder 

 rails ; (4) moderate speeds. 



2. Anschutz Gyro-Compass. By G. K. B. Elphinstone. 



This apparatus is a compass in the true sense of the word; that is to say, it 

 takes up a definite direction on any part of the earth's surface, so that its axle 

 points to the true north and south, or is, in other words, parallel with the 

 meridian. This position is arrived at automatically no matter in what position 

 the compaiss is started. 



The apparatus consists of a rapidly rotating gyrostat enclosed in a casing so 

 suspended that the centre of gravity of the whole system is considerably below 

 the point of suspension, and on that account the system is acted upon by 

 gravity like a pendulum. The action of gravity is such as to keep the axle of 

 the rotating gyro always horizontal. 



When the axle of the gyro is pointing in any direction except parallel to the 

 meridian the gyro-wheel tends to maintain its plane of rotation fixed in space, 

 irrespective of the rotation of the earth, and the rotation of the earth would 

 merely carry round the gyro with its plane of rotation remaining parallel to its 

 original plane. 



Under these, conditions one end of the axle would dip down from the hori- 

 zontal or tangential position on the surface of the globe, and the other end 

 would incline upwards. This tendency, however, is opposed by the force of 

 gravity acting as described above, and there follows a precession turning the 

 axle towards the meridian, this precession continuing until the effect of gravity 

 has caused the axle to become horizontal once more. 



Should this condition be reached after the gyro-axle has crossed the meridian, 

 the further rotation of the earth will cause a reversal of the inclination of the axle 

 from the horizontal or tangential position on the globe, and on that account the 

 precession will be reversed. 



From the above it follows that the axle of the gyrostat would oscillate to 

 and fro across the meridian, the only cause for these oscillations to cease being 

 the friction of the suspension. In order that the system may take up a definite 

 position with good precision this friction has to be very small in amount, and 

 therefore the swinging to and fro would continue for a very long period of time. 

 To get over this difficulty a method of damping these swings without the intro- 

 duction of friction is required. This is obtained by making use of the current 

 of air set in motion by the rapidly revolving wheel. 



