256 PETTERSSON , OS WATEH AND ICE. 



volume of ice decreases^ in the vicinity of its melting point. 

 As I deem this fact of importance to raeteorology as well as 

 to hj^drography, I have tried to make the behavior of pure 

 ice in the vicinity of zero one of the main objects of ray in- 

 vestigation. 



The preceding exposition is only intended to give a gene- 

 ral view of the development of our knowledge of the proper 

 ties of pure Avater and ice, which Avas to be the first object 

 of my study [see page 253]. 



Regarding the problems II and III, viz. the properties of 

 ice from brackish water and oceanwater, no previous researches 

 have been published, nor has the change of volume etc. of 

 ice formed in the open sea formerly been subject to quantita- 

 tive measurements. 



The volumes of oceanwater. have recently been very care- 

 fully studied by L. F. Ekman, by means of Regnaulfs dila- 

 tometer. Mr H. Tornoe, hydrographer of the Norwegian 

 expedition, has repeated the determinations of Ekman with 

 the Sprengel pycnometer, another equally sensible instru- 

 ment, and obtained almost identical results. - 



I therefore thought it would be superfluous to again test 

 the dilatation of salt water with my own dilatometer and 

 resolved to confine my research to the dilatation of brackisl) 

 water of little saltness, an object of still greater interest for 

 my purpose, such water being formed by the melting of sea- 

 ice. By special permission from professor Ekman, I was 

 ' authorized to insert bis curves [the blue lines in plate 23] of 

 volume of salt water together with my own determinations 

 on pure and brackish water, which are marked in plate 23) 

 with black and red colours. 



1 Nor did Pliicker and Geissler observe anj* similar phenomeiioii. 

 This result is entirely new and is due to the larger scale and the refined 

 methods of measurement adopted in the present series of experiments. 



■^ The numbers given by Ekman [K. V. A:s Handl. 1870] being thns 

 confirmed by Tornoe [Norwegian Nortli- Atlantic Expedition 1876—1878], 1 

 think it superfluous to discuss here the previous determinations by Hub- 

 bard, Thorpe, Räcker, Karsten a. O. 



