INSTRUCTIONS TO MARINE METEOROLOGICAL OBSERVERS 55 



Direction of sioell 



[Direction /row which swell is moving] 



Period of swells. — Observations of length and height of the swell 

 are not so valuable as the period. The number of swells that pass 

 a given point in one minute may be taken as the period. On ship- 

 board this may be calculated by watching the rise and fall of a 

 patch of foam and noting the time interval. 



In so doing, rise and fall due to the true swell, and not the smaller 

 waves, should be noted. A series of such observations will give a 

 good approximation of the time interval in seconds or the period 

 expressed in number of swells in a minute. 



Observations of swell period, especially in connection with tropical 

 storms, will be appreciated. They should be written in the "Daily 

 Journal" or under "Kemarks." The entries should show clearly 

 wdiether they give the average interval in seconds or the number of 

 waves per minute. 



GALE, STORM, AND FOG REPORTS v 



Gales and storms. — A summary of every gale encountered should 

 be entered in the spaces provided on the form. Gale, or storm, re- 

 ports are desired for winds reaching force 8, Beaufort scale, except 

 that in tropical seas reports for wdnds of force 6 or higher are re- 

 quested. Special accounts of storms may be prepared on a separate 

 sheet and attached to the form. The report should especially include 

 shifts of wind, lowest barometer, highest wind force, and also the 

 time and ship's position and course when each occurred. Reports of 

 this character are very useful in determining the intensity of the 

 storm and the exact course of the center, and particularly valuable 

 for storms of tropical origin. 



Fof/s. — The local date and hour of entering and emerging from 

 fog should be given in the Fog Report, together with other special 

 information, as indicated by the headings. Under the heading "Gen- 

 eral character of fog" should be entered a word, or words, to indicate 

 character, whether dry, wet, light, dense, low, spotted, or in banks. 

 In case no fog is observed during the period covered by the report, a 

 statement should be made to that effect. Negative information is 

 sometimes of much value. 



SUPPLEMENTAL DATA FOR RADIO MESSAGES 



All observations sent by radio contain the four Universal groups, 

 the symbols for which are — 



YQLLL lllGG DDFww PPVTT 



