182 



Jlolbom and Day — Gas Thermometer at 



equipped with a bulb of Jena glass 59 111 between 250° and 

 500° in a nitre bath. These observations were designed partly 

 to verify the earlier observations below 500°, with which the 

 element T 2 was connected only indirectly by comparison with 

 Tj ; and partly to enable us to compare the absolute values 

 obtained from observations in the nitre bath and in the elec- 

 trically heated air bath. 



This nitre bath was considerably smaller than the one used 

 for the earlier observations and was heated electrically, whereby 

 we were enabled to secure constant temperatures more quickly 

 and more exactly. A wrought iron cylinder 12 e,n in diameter, 

 such as is used for the transportation of mercury, was cut off 

 at a height of 27 cm and fitted with a cover 2 cm thick, which 

 carried a turbine driven by an electric motor for stirring. 

 The heating coil was of bare constantan wire l-5 mm in diameter 

 wound in two parallel coils upon the cylinder, the insulation 

 being provided by a layer of asbestos board, and held in place 

 by smearing with clay. The whole was enclosed in a larger 

 fire-clay jacket and the space between closed in with asbestos 

 wool, giving a layer of air a centimeter or more thick about 

 the coil. This bath can be used up to 700°. 



4- Natural size. 



For temperatures below 300° where insulating liquids may 

 be used for the baths, an arrangement which did us exceed- 

 ingly good service certainly deserves mention in passing. A 



