296 



THE DEPTHS OF THE SEA. 



[chap. vii. 



This experiment at once proved the advantage of 

 the encased bulb. It was repeated with other ther-' 

 mometers with the same pressure and for the same 

 period of time, and it was found that while the mean 

 difference of the encased bulbs was only 0°'95, that of 

 the ordinary deep-sea thermometers was, as in No. 57, 

 7°'25. It follows, also, from these experiments, that 

 very nearly all the difference or error is due to pres- 

 sure on the full bulb, and that by encasing that bulb 

 we have a nearly perfect instrument. 



The next series of experiments was made to esta- 

 blish a scale by which observations by the ordinary 

 instruments might be approximately corrected for 

 pressure. The following table gives the errors of 

 six thermometers at different pressures. The 

 ' standard ' is an encased Miller-Oasella, the last 

 a registering minimum thermometer by Casella 

 enclosed in a hermetically sealed glass tube on Sir 

 William Thomson's plan. 



H m 



The mean difference for each 250 fathoms in each 

 thermometer is as follows : — 



