FLUID METHODS OF SURVEYING BOREHOLES 113 



in connection with the supply current from the surface. 

 The wire n is fastened to a pin. In the normal position 

 the mercury presses the needle against the compass 

 ring. The south pole of the needle is insulated, thus a 

 current through n and hi must pass through the north pole. 

 As soon as the dip is fixed, a pressure of air is blown on to the 

 surface of the mercury, freeing the needle. When the 

 pressure is taken off the needle settles. Now n and hi are 

 connected to the galvanometer and battery and the direction 

 of dip determined by noting that the deflection of the galva- 

 nometer is inversely proportional to the deflection of the 

 north pole, which information is provided by the opposite 

 points e and /. The demerits of the device lie in the steel 

 casing and air pressure interfering with the needle; still 

 the method is the forerunner of several continuous register- 

 ing devices using the same principle. Variations, to the 

 benefit of the device, will immediately suggest themselves, 

 such as non-metallic casings and insulating the pin to the 

 core of an electromagnet. 



The Kiruna Method. — This is an electrolytic precipita- 

 tion method devised by the Swedish Diamond Drilling 

 Company with the assistance of the Jernkontoret — the 

 Swedish Iron and Steel Society — and is named after the 

 famous South Sweden iron field where it was first employed. 

 Prof. Walfrid Petersson of the Royal Mining School, Stock- 

 holm, completed the analysis of the method. 



As previously discussed, the elliptic outline of a fluid in 

 an inclined container determines the dip angle, and the 

 major axis of it the direction of this dip. If two such 

 containers are rigidly connected a distance apart, the form 

 of the resulting ellipses and their major axes will fully 

 decide the dip in amount and direction. Certain terms 

 are necessary to a mathematical comprehension of the 

 principles involved, thus:^ 



1 Peteksson, W., Metoder for Matning av Avvikelser i DjupborrhS,!, Jern- 

 kontorets Annaler, pp. 224-262, 1922; also Eng. Min. Jour. Press, Vol. 117, 

 No. 17, Apr. 26, 1924. 



