ELEMENTARY THEORY OF MAGNETISM. 



II 



magnet pole diverge very greatly indeed as shown in Fig. 126, 

 that is to say, the magnetic field in the neighborhood of a pointed 

 pole is non-uniform to a high degree, and such a magnet pole has 

 a strong attraction for small particles of magnetic material. 

 Surgeons make use of a pointed magnet in removing particles of 



Fig. 12a. 



iron or steel from the eye. If it is desired to separate magnetic 

 particles from non-magnetic particles in a finely crushed ore, a 

 pointed magnet pole must be used to attract the magnetic 

 particles. 



12. Gauss's method for measuring the horizontal com- 

 ponent H' of the earth's magnetic field. From about 1860 to 

 1880 the measurement of the intensity of the horizontal com- 

 ponent of the earth's magnetic field, H r , by the method of 

 Gauss was of fundamental importance, because the tangent 

 galvanometer was then extensively used for measuring electric 

 current, and to measure an electric current by the tangent 

 galvanometer, the value of H' must be known. The tangent 

 galvanometer has, however, been superseded by the electro- 

 dynamometer (see description of Weber's form of electrodyna- 

 mometer in Art. 22) for the fundamental measurement of electric 

 current, and therefore Gauss's method is now important only in 

 the making of magnetic surveys. The method is however of very 



