Temperatures. Thermometers 151 



at the place of observation, since the thermometer was 

 last set. To set the index, a small magnet is passed 

 along the tube in the direction away from the bulb, 

 and the steel index follows it until the meniscus of the 

 liquid is reached. 



Fig. 49 is an illustration of a portion of the stem of 

 a maximum thermometer. 

 Mercury fills the bulb and 

 part of the stem, and a 

 steel index, provided with Ficy 49 



spring-like ends as shown, 



is contained in the space above the mercury. The 

 steel is not wetted by the liquid, and when the end 

 of the mercury column in contact with the index moves 

 along the tube while the temperature is rising, the index 

 is carried before it. On the retreat of the liquid during 

 a fall of temperature, the index retains its position. 

 The end of the index nearer the top of the mercury 

 column thus registers the maximum temperature re- 

 corded during the period of observation. To reset the 

 instrument, a magnet is used as indicated in the case 

 of the minimum thermometer. The stem of this ther- 

 mometer is also kept in a horizontal position. 



The above thermometers are known as Rutherford's 

 minimum and maximum thermometers. In another 

 fornij both minima and maxima of temperature are 

 registered by the same instrument. Six's thermometer 

 consists of a large bulb containing alcohol to which is 

 attached a long bent tube containing mercury in one 

 bend as shown. Two small indexes, provided with 

 springs, are placed in the alcohol at each end of the 

 mercury column. The remaining portion of the tube 

 and part of the cup at the top contain alcohol. 

 Expansion of the alcohol in the bulb and first part of 



