FIGURE 6. I 3 



GEOTHERMAL GRADIENT RECORDER 



tive end up. The photocell is connected as shown here; two wires 

 lead down into a suitable electrolytic solution which makes it a 

 silver voltammeter . You may remember that the silver voitam- 

 meter is used to determine the standard units of current. By 

 weighing on a standard analytical balance in the laboratory the 

 amount of silver plated out, we can determine directly the 

 amount of light that this instrument received over the period it was 

 used. This is a simple instrument. It can be replaced in the field 

 by SCUBA divers. The accuracy is very high. In fact, they are 

 hard to calibrate with conventional D'Arsonval meters because 

 they are based on the national current standard. 



The GEOTHERMAL GRADIENT RECORDER (fig. 6.13) is 

 listed in one of the handouts which you have. (It is a very early 

 model of I-q, a Sea Floor Geothernnal Probe. See appendix E. ) 

 This is a pressure-protected instrument. The strip chart re- 

 corder is in the center with the servosystem to the left. The am- 

 plifier, which is located toward the front just above the batteries, 

 is a modified hearing aid amplifier. The instrument is highly sensi- 

 tive, being accurate to less than a thousandth of a degree. The 

 temperature range across the chart may be adjusted. It may be 

 as great as half a degree Centigrade full scale. A socket is provided 



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