300 THE VOYAGE OF H.M.S. CHALLENGER. 



I. MEMORANDUM on the METEOEOLOGICAL OBSERVATIONS made during 

 the Voyage of H.M.S. Challenger, 1872-76, prepared by Staff- 

 Commander T. H. TIZARD, R.N., under the direction of Captain F. J. 

 EVANS, C.B., F.R.S., Hydrographer. 



The following Tables give in detail the meteorological observations taken on board 

 H.M.S. Challenger throughout the voyage, the instruments (with their necessary correc- 

 tions) having been furnished by the Meteorological Department of the Board of Trade. 



The observations were uniformly made at two-hourly intervals by the officer of 

 the watch, excepting at the hours of 6 A.M. and 6 P.M., when the instruments were 

 recorded by the Staff- Commander. 



From the 21st December 1873 to the 17th March 1874, the ship being then in the 

 southern part of the Indian Ocean, and for some days in the immediate neighbourhood of 

 the Antarctic Circle, hourly observations were made. 



BAROMETER. The barometer was suspended on the main deck, just outside the 

 captain's cabin, the cistern being 9i feet above the level of the sea. The same instrument 

 was used throughout the voyage. It was compared with the standard at Kew Observa- 

 tory before leaving, and on the return of the ship to England ; (also with the standard 

 instruments in the observatories at the Cape of Good Hope and at Sydney, N.S.W.) 

 its error remained constant throughout the voyage. 



The original readings have been corrected for this instrumental error and for 

 capillarity. They have been further reduced to a temperature of 32 Fahr. and sea-level. 

 No correction has been made for errors of observation. It appeared to us to be better 

 to leave such errors to be dealt with by meteorologists, and thus to avoid the risk, in 

 attempting to harmonise them, of losing an element by which the general value of the 

 record might be estimated. 



WIND. In accordance with the general custom on board ship the compass direction 

 of the wind was recorded at the time of observation : in the following tables its direction 

 has been referred to the true meridian. 



In describing the force of the wind and state of the weather the notation, as follows, 

 proposed by the late Admiral Sir Francis Beaufort, and now generally adopted, has 

 been employed. 



