Magnetic Observations on the Galilee 95 



b. Roll. This column records the average full angle through which the ship rolled, from 



side to side; it is double the recorded clinometer-readings. 



c. Sea. The state of the sea is indicated by the following symbols: 



B. — Broken or irregular sea. H. — Heavy sea. R. — Rough sea. 



C. — Chopping, short or cross sea. L. — Long, roUing sea. >S'. — Smooth sea. 



G. — Ground swell. M. — Moderate sea, or swell. T. — Tide rips. 



When different observers record the state of the sea independently, it frequently 

 happens that their estimates or designations vary. In many of these cases one 

 particular letter was selected, after a careful consideration of all the symbols 

 given by the various observers, supplemented by the recorded ship's roll, and by 

 other notes. 



d. Weather. The symbols denoting the state of weather at the time are those in general use : 

 b. — Clear, blue sky. I. — Lightning. s. — Snow. 



c. — Clouds. m. — Misty. /. — Thunder. 



d. — Drizzling or hght rain. o. — Overcast u. — Ugly appearances, threatening weather. 



/, — Fog or foggy weather. p. — Passing showeis. v.— Variable weather. 



g. — Gloomy, dark, stormy. q. — Squally. w. — Wet or heavy dew. 



h. — Hail. r. — Rain. z. — Hazy weather. 



Weights. — The figures given in the column marked "Wt." are the weights assigned 

 the results on the following scale, which expresses, in a general way, the conditions as to sea, 

 weather, instruments and experience under which the observations were made: 1 denotes 

 severe or adverse conditions; 2, medium conditions; and 3, favorable conditions. 



The application of variation corrections to the observed results on account of the 

 numerous variations of the Earth's magnetism, e. g., diurnal variation, secular variation, 

 magnetic perturbations, etc., is deferred to the volume in which all the magnetic data, 

 obtained both on land and sea, will be summarized and reduced to a common epoch. 

 (That volume. No. V, can not appear until some time after the completion of the present 

 cruise of the Carnegie in 1917. Whether it will be worth while, in the case of the ocean 

 data, to apply any other corrections than those on account of secular change will there 

 receive consideration.)^ To avoid undue delay in the promulgation of the accumulated 

 data, and in view of the inaccuracies of the magnetic charts at present in use, it is con- 

 sidered best to publish the observed results as obtained with no corrections applied, except 

 the reductions to the magnetic standards of the Department, as fully explained in the 

 section on this subject. However, since for the magnetic elements tabulated the precise 

 data and local mean time of each observation are given, the reader is supplied with the 

 required information in case, for some purpose of his own, he desires to reduce the observed 

 values to some mean time. 



Local Magnetic Disturbance. — As in Volumes I and II, the asterisk (*) is used through- 

 out to indicate a station where local magnetic disturbance is known to exist. 



Combining Weights Assigned to Different Instruments and Methods. 

 The tabulated values of the magnetic elements are usually the weighted means of two or 

 more results, obtained by means of two different instruments, or by two different methods. 

 To obtain the weighted value of the declination, the results of 



Compass RIA (prism) was given a weight 1 l^j-uise I 

 RIA (alidade) was given a weight 1 J 

 RIB (prism) was given a weight 1 1 q^.^^^^ jj 

 RIB (alidade) was given a weight 1 j 

 R3C (prism) was given a weight 2 1 

 R3C (alidade) was given a weight 2 q^.^^^^ jjj 

 D2 (prism) was given a weight 1 

 D2 (alidade) was given a weight 1 j 



'Volume IV is to contain the magnetic-survey results 1914-1917 and reports on special researches. 



