468 
Dll. J. H. YIXCENT OX THE DENSITY AND COEFFICIENT 
consideial^le jjressure, since each new layer as it was formed became the vehicle ot 
transference of heat ujDwards from the underlying water. Ice is one of the most con¬ 
tractible of solids l.)y fall of temperature, and thus when the whole of the water was 
frozen, it must have Ijeen considerably denser than it would he at 0° Cf The sides of 
tlie somewhat narrow tube would tend to jDrevent the ice assuming its 2 :)roper density 
as the temperature rose to 0° C. It should be noted that if the mean temjDerature of 
Bunsen’s ice column was 4° or 5'^ below zero, this would suffice for the somewhat high 
value which he oljtained. There is another and more serious objection to Bunsen’s 
method. Any attempt to get ice exactly at 0° C. by surrounding it with an ice 
jacket may result either in the resulting temperature being lower than 0° C., through 
the observer not allowing a sufficiently long time for the ecpialisation of temperature 
or, on the other hand, may result in some of the ice melting. In either case the 
value obtained for the density will be too high. None of these objections apply to 
Plucker. and Geissler’s work. 
Barnes (‘ Physic. Review,’ July, 1901) has recently determined the density of 
natural ice by weighing selected specimens in water. His results give the same 
density for old and new ice. The mean value ol)tained (ex])ressed in grammes per 
cid). centim.) was ’91649. 
Si/no2:>sis of Previous Worlc. 
In order to facilitate reference, the results of previous workers have been set out 
in Table I., which gives the methods adopted, the variety of ice used, and the results 
obtained ])y different observers. 
In Table II. the results for the two kinds of ice are sejDarately set forth. The 
^^■ork of Marchand is omitted altogether from this talJe, as he did not state what 
kind of ice he used. The value of the density obtained for old pond ice by Nichols 
is also not included. The mean result for the density of natural ice at freezing point 
is '9176 gramme per culr centim., while that of artificial ice is '9165 gramme per 
cub. centim. 
If, however, we neglect Dufour’s value, we obtain the result •9162 gramme per 
cub. centim. for artificial ice. 
Only one estimation of the dilatation of natural ice is available. It is •0001125 
for the culucal coefficient of dilatation for 1° C., while three results are available for 
artihcial ice. The mean value is •OOOlOO for the cubical coefficient of dilatation 
for 1° C. 
Only one direct determination of the cubical expansion of artificial ice is to hand. 
This was oljtained by Plucker and Geissler, and is •0001585 for the cubical 
coefficient of dilatation for 1“ G. 
In both Tables I. and II. the cubical coefficient only has been tabulated. In those 
cases in which the linear coefficient was actually determined, the cubical coefficient 
