42 



NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, B.C.. 



57. Negretti and Zambra's Patent Self-Registering 

 Maximum Thermometer, for recording the Temperature 

 of Mines, Thermal or Boiling Springs, Atmospheric or Earth 

 Temperature, &c., &c. 



This Thermometer has its scale divided and figured 

 upon the stem, the REVERSE of an ordinary Thermometer 

 the reading commencing from the end of the tube and not at 

 the bulb. The stem or tube is mounted in and protected by 

 a stout glass shield, the bulb of the Thermometer being 

 uppermost, and all mercury passing the bend or contraction 

 in the tube will by gravity fall to the opposite end, and 

 be detained and measured. The whole instrument is 

 conveniently mounted in a round copper or brass case, with 

 a handle or ring attached to the top for suspending the 

 Thermometer. Fig. 48. 



FIG. 48. 



FIG. 49. 



In use, the Instrument is suspended by the ring 

 attached to the top of the metal mounting, and as it enters a 

 heated atmosphere the mercury in the bulb expands into the 

 tube, passing the bend or contraction* near the bulb ; 

 whatever quantity of mercury passes the bend will remain in the tube, and 

 not recede when the temperature cools ; should thirty or forty degrees of mercury 

 pass, it will of its own weight, fall to the end of the tube ; should it not do so, 

 hold the Thermometer in an oblique position, the bulb end being lowest so that 

 the mercury in the tube may very gradually descend until it touches any 

 mercury at the bend,f if now the bulb end be raised the mercury will again 

 descend carrying with it any small particles that have passed the bend- 

 When the mercury has all been collected at the end of tube, read off in degrees 

 on the thermometer scale its indication, and that will be the Maximum 

 Temperature. 



To re-set the Thermometer hold it bulb downwards, and swing it back- 

 wards and forwards, to force back the excess of mercury, beyond the present 

 temperature, into the bulb. This precaution should always be observed 

 before commencing to take an observation. 



Price, in Strong Metal Mountings. 1 10 



57*. In our Section, " Thermometers for Special Purposes," will be found 

 woodcuts of several other forms of these Instruments, with details as to 

 their construction and use, and of fig. 49, for obtaining the temperature of 

 Springs or Wells or Earth Temperatures, see also No. 46. 



* Sometimes a bend and sometimes a contraction is used to separate the indicating mercurial column, 

 t The tube should not be held upright, or portions of the mercury may pass by the bend into the bulb. 



