FLUID METHODS OF SURVEYING BOREHOLES 111 



with the immersion body or to pull it out of the fluid. This 

 is done by automatic switching for the drive ii 12- The 

 material of the body immersed may be altered to suit the 

 fluid being used, and this latter may be etching or coloring. 

 With colored fluid the curves can be indicated direct on to 

 paper. 



On taking a measurement the clockwork is adjusted so 

 that the needle is clamped about 10 min. after entry 

 into the hole. After this arrest, the body is immersed 

 in the fluid for about 2 min. and is then raised out of it 

 automatically. Since the motions can be easily fixed 

 beforehand aboveground, one is informed as to how much 

 time is required for effecting complete marking. 



The apparatus has the advantage of great simplicity in 

 construction and manipulation. Even if the measurements 

 are restricted to a definite time and the apparatus must 

 be let down anew for each reading, there is the advantage 

 that after once adjusting the mechanism everything is 

 automatically controlled without special attention on the 

 part of the people attending the device. Again to be 

 able to indicate the position of the fluid surface directly 

 on to a paper will, in many cases, be most convenient and 

 of advantage in the evaluation of test results by computation 

 or graphically. The measurements need not be dependent 

 on a time interval for operation; an electromagnet, surface 

 operated, might be used to arrest the spring. The usual 

 demerits of fluid methods, i.e., single readings, capillarity, 

 etc., hold, but the great defect of the method is the lack 

 of a centering device. 



Any method which gives the direction of deviation in 

 the hole is unacceptable if it has no device, as, say, in 

 Erlinghagen's apparatus, to prevent turning of the hole 

 on insertion or extraction, or some other means of showing 

 the direction in situ. 



Macfarlane's Apparatus. — G. C. Macfarlane's apparatus 

 was probably the first that utihzed the electric current 

 and galvanometer which appears such an important feature 

 in subsequent inventions. He measured the electric cur- 



