7° 



The National Geographic Magazine 



able to predict to the mariner, with a 

 reasonable degree of probability, all 

 necessary meteorological data for any 

 period of the year. 



For convenience, we will only con- 

 sider the Pilot Chart of the North At- 

 lantic, the principal references to which 

 will also apply to the chart for the North 

 Pacific. 



A short resume of the manner in which 

 information is collected for this chart, 

 followed by a general description of the 

 subject-matter, will give the best idea 

 of its use and value. The data col- 

 lected by Maury from 1844 to 1861 were, 

 generally speaking, taken from the log 

 books of vessels for individual 5° squares 

 on the world's water surface, and in the 

 majority of cases gave information for 

 each hour of the day in whatever part 

 of the world any observing vessel hap- 

 pened to be. 



About twenty years ago it was 

 deemed advisable to alter this system of 

 collecting information, and the ob- 

 servers of the office were furnished with 

 a blank observation book, in which the 

 data required were to be taken by all 

 observers only once a day and at the 

 same instant of time — Greenwich mean 

 noon. The observations thus recorded 

 give the direction and force of the winds 

 the reading of the barometer and ther- 

 mometers, the temperature of the water, 

 the character and percentage of cloud, 

 visible, and the character of the sea. 

 Immediately upon the arrival in port of 

 a vessel taking such observations, these 

 weather reports are sent either by mail 

 or through the United States consul to 

 the Hydrographic Office, where the in- 

 formation mentioned above is plotted 

 on a synoptic chart. This chart is di- 

 vided into squares of 5 degrees of lati- 

 tude and 5 degrees of longitude, and 

 each element of information previously 

 mentioned, except clouds and the state 

 of the sea, is indicated in its respective 

 square by a particular symbol. Through 

 inability to get the information quickly 



(as very frequently the record of a sail- 

 ing vessel does not get to the Hydro- 

 graphic Office until a long time after the 

 observations were taken) , it requires 

 many months before all the records for 

 any one year for each individual square 

 can be collected and plotted. A sepa- 

 rate synoptic chart is used for each day 

 in the year. Eventually each element 

 is averaged for each month of each year 

 during which the observations have been 

 taken, and a mean of each month of all 

 the years is transferred to the pilot 

 charts proper. 



EXPLANATION OF NORTH ATLANTIC 

 PILOT CHART FOR FEBRUARY, 1903 



All the possibilities and recommen- 

 dations for the coming month relating 

 to winds, calms, fog, gales, weather 

 forecast, barometric and thermometric- 

 data, and steamer and sailing-vesseL 

 routes are noted in blue. All mat- 

 ter noted in red relates to what has- 

 actually occurred in the past, and is va- 

 riable in character and not possible of 

 prediction with any degree of certainty. 

 For instance, the fed lines, of which 

 there are so many on the accompanying 

 chart,* represent the paths of the centers 

 of storms which have actually occurred 

 during the last five years. Derelicts and 

 wrecks, drifting buoys, icebergs, and 

 field ice which have been actually seen 

 and reported during the preceding month 

 are noted in red, the positions indicat- 

 ing to the mariner the region in which 

 they are likely to be found. 



This chart thus becomes a continuous 

 warning to seamen for the month on 

 the first day of which it is issued, and 

 is of practical economic benefit, in that 

 it operates to shorten ocean travel and 

 to lessen dangers to life and property. 

 The information given is considered so 

 important that the agents of many of 

 our great transatlantic liners telegraph 



*The chart is issued as a Supplement to 

 this number of the National Geographic 

 Magazine. 



