30 INSTRUCTIONS TO MARINE METEOROLOGICAL OBSERVERS 



the injection pipe where the circulation is locally reduced and where 

 pockets of warmed water can collect, the readings will be higher 

 than the true ocean temperature. However, errors on this score will 

 be avoided if the thermometer is mounted on the centrifugal pump 

 or at some point on the intake pipe between the pump and the ship's 

 side. It has been found by experiment that the best method of 

 installation is to fit the thermometer in a stainless steel tube, the 

 lower end of which is bathed by the incoming sea water. This lower 

 end of the tube should be filled with enough mercury to surround 

 the bulb of the thermometer completely, thus assuring good conduc- 

 tion of heat between the sea water and the bulb. 



The practical disadvantages peculiar to the condenser-intake 

 method can be serious. In the first place, there is the difficulty of 

 finding a place of installation for the thermometer which combines 

 the desirable qualities of proper exposure and accessibility. In the 

 second place, there is the ever-present danger of error of parallax in 

 reading the thermometer. It is not often possible to install the 

 thermometer in a place which affords a suitable exposure and at the 

 same time perndts the eye to be on a level with the top of the fluid 

 without tlie observer assuming an awkward or uncomfortable pos- 

 ture. In the third place, there is the necessity of securing the coop- 

 eration of the engineer on duty at the time that a meteorological 

 observation is made. The engineer should realize that a {greater 

 degree of accuracy is required in obtaining the ocean temperature 

 for the weather report than in noting the approximate tempera- 

 ture of the water circulating tifrough the cooling system. 



The condenser-intake method is the simpler and shorter means of 

 obtaining the water temperature. It is the more certain method and 

 the more accurate, where the required standards of installation 

 and of carefnl observation are met. However, circumstances vary 

 greatly on different ships, and tlie selection of the method to be used 

 should be left to the judgment of tlie individual observer. He should 

 make the choice after a careful consideration of the conditions exist- 

 ing on his shi]:). That method which will consistently give the most 

 satisfactory results should, of course, be employed. 



An entry should be made in the appropriate space on Form 1210A 

 to show which method is used in securing sea-water temperatures. 



PART IV. INSTRUCTIONS FOR TAKING AND RECORDING 

 WEATHER OBSERVATIONS 



For many years, vfind and weather and condition of the sea have 

 been subjects of daily entries in the ship's log, hence the taking of 

 systematic observations for the Weather Bureau does not involve 

 much additional time. However, weather conditions are recorded 

 in somewhat more detail than in the ship's log: moreover, the read- 

 ings of the barometer and thermometer are used in preparing weather 

 majis, hence their errors must be known so that corrections may be 

 applied. The proper methods of installing, reading, and caring for 

 the meteorological instruments are fully described in Part III. 



The observations are recorded on special forms (1210A-Marine) 

 provided by the Weather Bureau. Ships reporting by mail enter 



