Figure B-25. Stratoeumnlus not formed by spreading 

 out of cumulus. 



Figure B-26. Cumulus and stratocumulus. 



of the streaks of foam which are formed. Do not 



use the Beaufort'fi Force nu7n'ber8 when record- 

 ing lo-ind speed on the A-Sheet. 



B-7 Temperature of the Air. — The air tem- 

 perature should be read from the dry bulb of a 

 sling psychrometer and recorded on the A-Sheet 

 to the nearest tenth degree. The wet-bulb read- 

 ing of the sling psychrometer should be read and 



Table B-3. Wind force descriptive scale and velocity 

 from WMO Code 1100 



Beaufort Mean Velocity 

 Number Descriptive Term In Knots 



Calm Less than 1. 



1 Light air 1 to 3. 



2 Light breeze 4 to 6. 



3 Gentle breeze 7 to 10. 



4 Moderate breeze 11 to 16. 



5 Fresh breeze 17 to 21. 



6 Strong breeze 22 to 27. 



7 Near gale 28 to 33. 



8 Gale 34 to 40. 



9 Strong gale 41 to 47. 



10 Storm 48to55. 



11 Violent storm 56 to 63. 



12 Hurricane 64 and over. 



Figure B-27. Measuring wind speed and direction 

 with Wind Measuring Set (AN-PMQ-5A) . 



recorded to the same degree of accuracy. It Is 

 important that the temperature of the dry-bulb 

 and also the wet-bulb temperature be measured 

 by a sling psychrometer since this method is 

 more accurate than that of stationary thermom- 

 eters. Furthermore, the formula employed for 

 determining the i-elative humidity from the 

 readings of a psychrometer is not applicable to 

 the readings of a stationary wet-bulb thennom- 

 eter. If a sling psychrometer is not available, 

 the free-air temperature should be read from 

 an ordinary thermometer exposed to the free 

 air on the windward side of the ship under 

 conditions that eliminate as completely as 

 possible the effects of extraneous sources of heat. 

 The mercury bulb of the wet-bulb ther- 

 mometer in the sling psychrometer is covered 

 with a muslin wick. The wick must be wet with 

 fi'esh water before each observation. The wick 

 must be kept clean and free of salt. 



B-8 Barometric Pressure. — Atmospheric 

 pressure usually is measured aboard ship with a 

 precision aneroid barometer. Barometric pres- 

 sure should be recorded on the A-Slieet in inches 

 of mercury or millibars after applying the cor- 

 rection to the barometer reading. The correction 

 tag for the barometer usually is posted in a 

 convenient place near the barometer. Be sure to 

 indicate the units of measurement. 



B-8 



