AUXILIARY REGISTRATIONS IN BOREHOLE SURVEYS 35 



flask has a screw top and suspending device. Its base is a 

 pointed lead end. 



After the flask has hung a long time at the spot being 

 measured, it is rapidly taken out and the temperature of 



Shaft ,d Freezing Pipe 



Lead d» '"Vacuu^ 



Fig. 14. — The Mommertz low temperature borehole thermometer. 



the solution read. This gives the temperature at the said 

 spot after due allowance for the fluid being used. The 

 time needed for the apparatus to assume the temperature 

 of its surroundings is decided by trial for each case. 

 The results are more or less approximate 

 but useful. 



b. Measuring Increase of Temper- 

 atures. — There are many kinds of maxi- 

 mum and minimum thermometers in 

 use. A favorite type of maximum ther- 

 mometer is that in which the capillary 

 is left open and ground off into a fine 

 point with a reservoir surrounding it for 

 the overflow. This overflow can be 

 measured in various ways against known 

 bath temperatures. The Hallock^ type 

 has a secondary capillary for measuring 

 the separated mercury. 



A well-known type of maximum and 

 minimum thermometer is that of Six 

 (Fig. 15) in which the liquid is alcohol 

 in the tube A at the end B of which is a thread of mercury 

 BC, the remaining part of the thread and part of the bulb B 

 being again alcohol. The former end of the thread is for 

 minimum and the latter for maximum readings. There are 

 two indexes, one of glass the other of iron or both of glass 



1 Johnson and Adams, Econ. Geol., Vol. 11, pp. 741-762, 1916. 



Fig. 15.— The Six 

 maximum and mini- 

 mum thermometer. 



