Thermometer adapted to Deep-sea Soundings. 397 



in a strong wrought-iron cylinder tilled with water, and submitted 

 to hydraulic pressure, which could be raised gradually till it reached 

 three tons upon the square inch ; and the amount of pressure could 

 be read as the experiment proceeded, upon a gauge attached to the 

 apparatus. 



Some preliminary trials made upon the 5th of May showed that 

 the press would work satisfactorily, and that the form of thermo- 

 meter proposed would answer the purpose. 



These preliminary trials showed that, even in the thermometers 

 with protected bulbs, a forward movement of the index of from o, 5 

 to 1°F. occurred during each experiment. This, however, I be- 

 lieved was caused, not by any compression of the bulb, but by a real 

 rise of temperature, due to the heat developed by the compression of 

 the water in the cavity of the press. 



This surmise was shown to be correct by some additional experi- 

 ments made last week to determine the point. On this occasion 

 the following thermometers were employed : — 



No. 9645. A mercurial maximum thermometer, on Prof. Phillips's 

 plan, enclosed in a strong outer tube containing a little spirit of wine, 

 and hermetically sealed. 



No. 2. A Six's thermometer, with the bulb protected, as proposed 

 by myself, with an outer tube. 



No. 5. A Six's thermometer, with a long recurved cylindrical bulb, 

 also protected in a similar manner. 



No. 1. Six's thermometer, with cylindrical bulb of extra thickness, 

 not protected. 



No. 3. Six's thermometer, with spherical bulb, extra thick glass, 

 not protected. 



No. 6. Admiralty instrument, Six's thermometer, ebonite scale, 

 bulb not protected. 



No. 9651. An ordinary Phillips's maximum mercurial thermo- 

 meter, spherical bulb, not protected. 



The hydraulic press was exposed in an open yard, and had been 

 filled with water several hours before. A maximum thermometer, 

 introduced into a wrought-iron. tube filled with water, open at one 

 end to the outer air, closed at the other, where it passed into the 

 water contained in the press, registered 46 0, 7 at the commencement, 

 and 47° at the end of the experiment. Temperature of the external 

 air 49° F. 



In commencing the experiment, the seven thermometers under trial 

 were introduced into the water in the cavity of the press, and after 

 a lapse of ten minutes the indices of each were set, carefully read, 

 and each instrument was immediately replaced in the press, which 

 was then closed, and by working the pump the pressure was gra- 

 dually raised to 2^ tons upon the inch. It was maintained at this 

 point for forty minutes, in order to allow time for the slight elevation 

 of temperature caused by the compression of the water to equalize 

 itself with that of the body of the apparatus. At the end of the forty 

 minutes the pressure was rapidly relaxed. A corresponding depres- 

 sion of temperature was thus occasioned, the press was opened im- 



