12 THE AIR 



that very high temperatures are the rule, even within 

 the tropics ; while low temperatures prevail only in 

 the vicinity of the Arctic and of the Antarctic regions. 

 The borders of an ocean, in which the prevailing wind 

 is off-shore, in the tropics frequently show a lowered 

 air temperature, on account of the cold upwelling 

 water drawn up from the depths by the blowing away 

 of the warm surface water. On the other hand, the 

 borders of an ocean, in which the prevailing wind is on- 

 shore, often has a higher air temperature on account of 

 the warm surface water driven in from lower latitudes. 

 What may be termed " normal conditions of tem- 

 perature " are considerably deranged by local causes 

 in different parts of the globe — as, for instance, off 

 Cape Guardafui, on the East Coast of Africa, where 

 the changing of the monsoons substitutes an on-shore 

 for an off-shore wind, giving rise to upwelling of cold 

 water and banking up of warm water alternately. 

 Other instances are found off the Cape of Good Hope, 

 the Banks of Newfoundland and the Falkland Islands, 

 where ocean currents of different temperature meet, 

 and the same area is occupied at different times by 

 water of varying origin and temperature, which reacts 

 on the air. 



Instruments. 



It may be remarked that, as a rule, there is not 

 much choice in the placing of meteorological instru- 

 ments on board ship ; this follows from the structure 

 of the vessel and the exigencies of her special service. 

 Besides, the instruments must be placed in the handiest 

 position for observers, who may have to consult them 

 without quitting their posts or otherwise interrupting 

 the duty of the moment ; hence the routine observations 

 made on board ship, useful as they are, leave a good 





