484 Dr. W. A. Miller on a Self-registering Thermometer [June 17, 



press would work satisfactorily, and that the form of thermometer pro- 

 posed 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 believed 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 experiments 

 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. I. 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 thermometer, 

 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°'/ 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 instru- 

 ment was immediately replaced in the press, which was then closed, and 

 by working the pump the pressure was gradually 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 compres- 

 sion 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 cor- 

 responding depression of temperature was thus occasioned, the press was 

 opened immediately, and the position of the indices of each thermometer 

 was again read carefully ; and the water was found to be at a temperature 

 sensibly lower than before the experiment began, by about o, 6 F. By this 

 means it was proved that the forward movement of the index in the pro- 

 tected thermometers, amounting to 0°*9, was really due to temperature, 



