TEMPERATURE OF THE SEA, ETC. 633 



Comparing the sea in different parts, the proportion between 

 chlorine and sulphuric acid — 



In the Atlantic is - - - 10,000 to 1,188 



In the sea between the Faroe Isles, 



Iceland, and Greenland- - 10,000 to 1,193 



In the German Ocean - - 10,000 to 1,191 



In Davis Strait - - - 10,000 to 1,220 



In the Kattegat - - - 10,000 to 1,240 



The proportion of sulphuric acid increases near shores. 



4. Surface Temperature of Sea-Water. 



The mean monthly values from hourly observations in Van 

 Eensselaer Harbour, at a depth of 4 feet were : — 



1853, September, 29°- 1, October 28° -8. 

 From November to March, 28° '7. 



1854, April, 28° -8, May, 28° '9. 

 „ June, 30°- 3, July, 32° -3. 



„ August, 31° -8, September, 31°- 3, October, 30° -9. 

 After November 1854 the readings remained constant at 29° "0. 



5. Measuring the Specific Gravity of Sea Water. (Die 

 zweite deutsche Nordpolarfahrt, vol. ii. p. 667.) 



A very complete series of determinations of the specific gravity 

 of sea-water at the surface and at various depths was made by 

 Dr. Borgen with a very delicate glass hydrometer. A full account 

 of the results is given in the excellent record of M. Koldewey's 

 Expedition to East Greenland. The instruments w^ere tested at 

 Gottingen by Professor Kohlrausch before the Expedition sailed. 

 In working out the results the temperatu.re -\-\5>° C., or 59° F., 

 was taken as the standard temperature, and the tables of Dr. Gerlach 

 on the specific gravities of salt solutions of different strengths and 

 temperatures (Freiberg, 1859) were employed. For other tem- 

 peratures than +15° C., a correction was required for the change 

 of volume of the glass. 



As these tables will be useful for working out the results of 

 any observations which may be made on the specific gravity of 

 sea-water, and will at once give the relative strength of the salt- 

 water when its temperature is known ; the portion of them which 

 may be required is added to the Manual, and also the table of 

 corrections for the change of volume of glass for different tem- 

 peratures. 



To make an observation, the reading of the hydrometer must 

 be taken and also the temperature of the water ; multiplying the 

 observed reading of the hydrometer by the correction for the 

 observed temperature, and substracting the result from the reading 

 of the hydrometer, we get the specific gravity at 15° C. ; on 

 referring to the table of strengths of solution the per-centage of 

 salt in the sea is obtained. 



