50 INSTRUCTIONS TO MARINE METEOROLOGICAL OBSERVERS 



rinder Avater. At niglit tlie entire huchet sliould be carried to X\w. 

 nearest deck light (unless tlie observer lias provided himself with 

 a flashlight) ; the thermometer should be read there while its bulb 

 is still in the water. 



7. After every observation, leave the bucket upside down in order 

 that all the water may drain out. 



When the condenser-intake method is employed, the observer will 

 be obliged to secure the reading by telephoning to the engine room. 

 In this case he should make sure that the reading reported to him 

 by the engineer on duty is the temperature of the water flowing 

 through the injection pipe at the time of the meteorological observa- 

 tion and not the last entry made in the engine room log. He should 

 satisfy himself, also, that the engineers are sufficiently interested in 

 the meteorological work to realize the importance of reading the 

 intake thermometer accurately to a fraction of a degree, if possible. 



In the column on Form 1210A, headed ''Temperature of water", 

 the reading obtained must be entered to the nearest whole degree 

 Fahrenheit or half degree Centigrade as a minimum standard of 

 precision. Better still, if circumstances assure the possibility of 

 securing greater accuracy, the reading to the nearest tenth of a 

 degree Fahrenheit or Centigrade should be entered. A common 

 practice has been to read the thermometer to the nearest even-num- 

 bered Fahrenheit degree or nearest whole Centigrade degree. Such 

 readings are practically useless. 



If the severity of the weather is such as to exclude the possibility 

 of making a bucket observation on any particular day, observers in 

 the habit of using the bucket method should leave the space for 

 water temperature blank. A condenser-intake reading should not be 

 recorded as a substitute unless it is so labeled. 



The various problems and difficulties connected with the taking of 

 sea-surface temperatures are outlined in more detail on pages 29 to 

 30. Observers are urgently requested to study those paragraphs in 

 order that they may acquire a full appreciation of the care which 

 must be exercised if the desired standards of accuracy in the making 

 of ocean-temperature measurements are to be attained. 



Temperature of the wet hulh. — The temperature of the so-called 

 "wet-bulb" thermometer is necessary in determining the amount of 

 moisture present in the atmosphere, as previously indicated. Just 

 as in the case of the air temperature, the wet-bulb temperature should 

 be obtained correctly to tlie nearest tenth of a degree Fahrenheit, if 

 possible, and so entered in the column headed "Temperature of wet 

 bulb" on Form 1210A. Such exactness is necessary because the 

 difference between the air and wet-bulb temperatures must be deter- 

 mined as accurately as possible. An error of 1° F. in recording the 

 true depression of the wet bulb results, at ordinary temperatures, in 

 an error of from 5 to 10 percent in the computation of the humidity. 



In the past the wet-bulb temperature has usually been obtained 

 on shipboard from the reading of a stationary thermometer whose 

 bulb is tightly fitted with a piece of muslin, to which one end of a 

 cotton wick is attached. The other end of the wick is allowed to 

 stand in a reservoir of water. This arrangement keeps the muslin 

 moist, with the result that evaporation is continually taking place 

 around the thermometer bulb. 



