in the Ticcnty Years before 1895 75 



or nearly the same temperature, they may be used for giving 

 the specific gravity of the water. If they have not, or if the 

 determination is of especial importance, then a precisely similar 

 series of observations must be made in distilled water of the 

 same temperature, and variations of temperature amounting 

 to 0-3 C. are then inadmissible. 



When the corresponding series of observations has been 

 made in distilled water, and they have had the small stem 

 correction applied so as to give the displacing weight in distilled 

 water at the exact stem divisions observed in the sample 

 water, we have nine pairs of readings, each pair giving the 

 weights of equal volumes of distilled water and of the sample, 

 and therefore each pair giving by their ratio an independent 

 determination of the specific gravity of the sample referred 

 to that of distilled water of the same temperature as unity. The 

 mean of the nine observations gives a result which, according 

 to the doctrine of probabilities, should have a precision three 

 times greater than that of a single observation. Although 

 much may be done to avoid a large range of temperature 

 of observation, there will always be some difference in the 

 temperatures at which the specific gravity of the various 



;>les is observed, and as a similar variation would take 

 place in the unit to which they are referred, we effect a reduction 

 to their value, taking the density of distilled water at 4 

 (as unity). This is obtained by multiplying the figures obtained 

 as above for the specific gravity by the weight of one cubic 

 <>f distilled water at the temperature of observation. 

 This is one of the physical constants which have been deter- 

 mined with the greatest care and presumably with the greatest 

 precision, and therefore, if reductions are to be admissible 



!. this one can be made with tin* least fear of error. The 

 specific gravity multiplied by this weight of unit volume of 

 distilled water of the same temperature gives the density of 

 pie water at that tenijM-r.it HIT. tli.it is, it givo tin- 

 weight of one cubic centimetre of it in grammes. It may 

 also be correctly described as the specific gravity of the water 



be temperature, th.it of di-till.-d \v.itT .it 4C. being 



