256 JAKOB SCHETELIG. 



ing. The hydrometer is loaded with weights until it floats in 

 the liquid; and at the same time the temperature of the Hquid 

 is determined. If now the absolute weight and volume, and the 

 coefficient of thermal expansion of the hydrometer and weights 

 he known, the specific gravity of the liquid at the temperature 

 observed, can be determined with theoretically absolute accuracy. 

 For further particulars, the reader is referred to Prof. Nansen's 

 paper. 



The shape of the hydrometer of total immersion will be 

 seen from PI. 23, figs. 1 and 2. 



The appliances necessary for making the determinations, in 

 addition to the hydromerter itself, are: 



A glass cylinder, proportioned to the size of the 

 hydrometer; 



Stirrer for this ; 



A water-bath, suitable for the cylinder, provided 

 with stirrer. The bath may be dispensed with, if a 

 Dewar's cylinder is used; 



Two or three small thermometers, as sensitive as 

 possible, divided into tenths of a degree Centigrade; 



A lens for reading the thermometers; 



A set of spiral weights of platinum or platinum- 

 iridium (PL 23, fig. 4); 



A couple of spirals of platinum or platinum-iridium 

 were (PI. 23, fig. 3), with two arms upon which to hang 

 the weights; and 



A good pair of tweezers with ivory points for the 

 weights. See moreover PI. 23. 



Two hydrometers of total immersion, from Küchler at 

 Ilmenau, made of Jena Glass No. 16'" were used for the daily 



