FLUID METHODS OF SURVEYING BOREHOLES 101 



independent of each other. As soon as valve V2 is opened 

 by way of the coil, hook, and rod the needle is arrested 

 against a stop head e, chamber 1 is full open and chamber 4 

 discharges. A circular scale is etched on the inner wall of 

 chamber 3 for measuring the deflection of the colored sur- 

 face. The whole apparatus is guided by three skids / and 

 these with a base plate strengthen the instrument, guide 

 it into the hole and center it. On reaching the spot to be 

 investigated in the hole, coil d2 is first excited from the sur- 

 face which causes hook c^ to pull up and spring Si opens 

 valve Vi to chamber 3. The colored fluid flows in from 

 chamber 2 and indicates its position on the walls of 3. 

 After about 10 min. coil Ci is similarly operated by excita- 

 tion from bank and so opens valve V2 and lets the fluid flow 

 out into chamber 4. At the same time the needle is 

 arrested. 



Now the apparatus is drawn to bank and the heights 

 of the highest and lowest positions of the color line are 

 easily read. This with the needle data gives the amount 

 and direction of the deviation. Over Nolten's method this 

 method has the advantage of certain reading, not confused 

 by subsequent readings produced by accidental change of 

 direction. Also the line is sharper and as the vessel is not 

 injured by the fluid it can be utilized longer. Furthermore, 

 the needle is not arrested by clockwork but at the direct 

 will of the surface operator and the spherical surface of the 

 glass magnifies the reading; it can be arranged to read to 

 10 min. of arc with precision verniers. Its disadvantages 

 are those of all fluid instruments as stated in the intro- 

 ductory note on this section. 



MacGeorge's Clinograph. — In any discussion dealing 

 with fluid methods of surveying boreholes prominence 

 should be given to the method devised in 1884 by E. F. 

 MacGeorge and tested at Sandhurst and Stawell in Victoria, 

 Australia. This because the method marked a significant 

 advance upon all preceding methods and instituted an 

 epoch of research into the problems attendant on borehole 

 deflection which is still active. The apparatus will be 



