REPORT ON THE PRESSURE ERRORS OF THE THERMOMETERS. 5 



say, approximately, somewhere about six tons weight per square inch. This external 

 shell is nearly filled with alcohol The main difference between this and the first invented 

 form of protected thermometer, which (so far as I know) was introduced by Sir William 



Thomson, 1 is simply that the bulb only is protected, the stem being exposed, and there- 

 fore the effects produced directly by compression are due solely to the stem of the 



1 " The Effect of Pressure in Lowering the Freezing-point of Water experimentally demonstrated," by Professor W. 

 Thomson (Pne. R.SJ1., February I860). See also the paper by Parrot (1833) quoted below. In this a protected 

 thermometer was undoubtedly employed ; but the protecting sheath was part of the wall of the compression apparatus 

 and was not attached to the thermometer itself. From a reference in this paper I was led to consult Lear's observations 

 on deep-sea temperatures. He appears to have measured these temperatures by bringing to the surface, with great 

 care, a considerable quantity of water from each depth. There was a thermometer in the collecting apparatus, with a 

 bulb of extra thickness ; but no recording index was employed, so as to show what was its indication under pr 



