24 



MR J. Y. BUCHANAN ON THE 



twenty-four hours' sojourn in the laboratory equalised their temperature and brought 

 it to agree sensibly with that of the air of the laboratory and that of the hydrometer, 

 which was always kept in the laboratory. By working according to this system, 

 the specific gravities of the waters obtained from different depths at the same station 

 were determined at the same time and at the same temperature, and their relative 

 specific gravities at a common temperature were thus given directly by experiment. 

 This is an important advantage, and it is often overlooked. 



A subjective precaution, but one of great importance for assuring accuracy of 

 observation, was adopted at the beginning of the voyage and was never departed 

 from. Before beginning to make hydrometric observations on the samples of water, 

 or to carry out any other operation, such as the boiling out of the gases or the deter- 

 mination of the carbonic acid, / locked the door of the laboratory, and it ivas not 

 unlocked until the operation was finished. Consequently none of my colleagues, or 

 anyone else in the ship, ever witnessed the determination of the specific gravity of 

 the water, or any other of the operations carried on in the laboratory, at any time 

 from the beginning to the end of the voyage. I found that exactness of observation 

 was promoted by freedom from disturbance. 



Table VIII.* 



Giving Duplicate Observations of the same Sample of Water with the same 

 Hydrom,eter differently weighted. 





Density observed with 







Density ob 



served with 





No. of 

 Saiiijile. 







DilTereiice. 

 OOIV-OOV. 



No. of 

 Sample. 







Difference. 

 OOIV-OOV. 













00 IV. 



oov. 







OOIV. 



OOV. 





120 



1-02412 



1-02411 



+ 1 



274 



1-02416 



1-02412 



-1-4 



127 



1-02414 



1-02409 



+ 5 



826 



1-02411 



1-02411 







135 



1-02406 



1-02413 



-7 



829 



1-02411 



1-02408 



+ 3 



139 



1-02407 



102414 



-7 



830 



1-02400 



1-02405 



-5 



181 



1-02428 



1-02427 



+ 1 



831 



1-02421 



1-02418 



+ 3 



After the Challenger Expedition I used in all my deep-sea work hydrometers with 

 sets of weights designed for making multiple observations in each water. The principal 

 stepping-stone between the Challenger hydrometer and that used in the investigations 

 of this memoir was one in which the observations were made in triplicate, the difference 

 between successive added weights being 0'25 or 0*3 gram. One reading was made near 

 the middle of the stem, and the other two were made near the middle of the lower and 

 the upper halves of the stem respectively. 



A very complete and important set of observations on this scheme was made in 

 1885, on a voyage from Southampton to Buenos Ayres, and then from Valparaiso 

 following the west coast of South America to Panama, and thence along the west coast 



* "Report on the Specific Gravity of Ocean Water," Physics and Chemistry, vol. i., Part II., Table VIII. 



