Velocity of Transmission of Disturbances through Sea-water. 517 



Observation and Calculation of the Density. 



In the " Challenger Report," vol. 1, 'Physics and Chemistry,' 

 p. 70 et seq., is given a table for calculating the density of a sea- 

 water at any temperature when its density at 15*56° C. is known. 

 To get the density of the Berry's Bay water at this temperature six 

 experiments were made on two samples collected at an interval of a 

 month. The water of the Bay is practically Pacific Ocean water, 

 there being to all intents and purposes no fresh water flowing into 

 the Bay. Four of the experiments were made by weighing a piece 

 of glass (English flint), both in doubly vacuum-distilled water and in 

 the sea- water ; and two experiments were made with a specific 

 gravity bottle. Both the glass and the water had been allowed to 

 stand in the balance case for seven hours before weighing ; the ther- 

 mometer used was a standard compared at Kew, the correction being, 

 as it happened, zero, for the temperature observed. The piece of 

 glass was suspended from the arm of the balance by a platinum wire, 

 the length of which was 28 cm. The weight of 1 metre of the wire 

 was 0'1004 gram, and the density was taken as 21. In each weighing 

 in water one half the wire was immersed. The sensitiveness of the 

 balance was such as to give readings of eight scale divisions per 

 milligram. The density of the sea- water is compared with that of 

 pure water by means of the formula 



in which p is the density of the water in which the glass is 

 weighed, 



G = mass of glass, 



g = density of glass, 

 W = apparent weight in air, 

 W'= apparent weight in water, 



a — density of the air during weighing, 



B = density of the brass weights = 8*4, 



P = mass of platinum wire = - 0281 12 gram, 



<p = density of platinum = 21. 

 p on the right-hand side is taken approximately. 



The above formula is got by neglecting 



pB \g p J p 



compared with W — W. 



In the present case this is equivalent to neglecting — 



0*00000815 gram in comparison with 4"93 grams. 



