22 ADMIRALTY INSTRUCTIONS. 



assisting to provide authentic data, collected from 

 all parts of the world, and ready for the use of 

 future labourers, whenever some accidental dis- 

 covery, or the direction of some powerful mind, 

 should happily rescue that science from its present 

 neglected state. But those hours of entry greatly 

 interfere with the employments of such officers as 

 are capable of registering those instruments with 

 the precision and delicacy which alone can render 

 meteorologic data useful, and their future utility is 

 at present so uncertain, that it does not appear 

 necessary that you should do more than record, twice 

 a day, the height of the former, as well as the 

 extremes of the thermometer, unless, from some 

 unforeseen cause, you should be long detained in 

 any one port, when a system of these observations 

 might then be advantageously undertaken. There 

 are, however, some occasional observations, which 

 cannot fail of being extensively useful in future 

 investigations : 



" 1. During the approach of the periodic changes 

 of wind and weather, — and then the hygrometer, 

 also, should find a place in the journal. 



" 2. The mean temperature of the sea at the 

 equator, or, perhaps, under a vertical sun. These 

 observations should be repeated whenever the ship 

 is in either of those situations, as well in the Atlantic 

 as in the Pacific ; they should be made far away 

 from the influence of the land, and at certain con- 

 stant depths, — suppose fifty and ten fathoms, — and 



