86 GEELMUYDEN. ASTRONOMICAL OBSERVATIONS. [NORW. POL. EXP. 



H. Latitude, Local Time, and Longitude. 



The time of observation is given by the hours and minutes of chronometer HohwO and 

 astronomical date. The Greenwich astronomical date and time is obtained by subtraction of the 

 corresponding hours and minutes of the preceding Table, and the local mean time by addition 

 of the numbers in the next column of the present Table, containing the correction of Hw to 

 local mean time. The sum of the numbers of this column and those of the preceding Table 

 will then give the East Longitude in time. 



For the latitudes determined by meridian altitudes of the Sun at sea, the date of local 

 Noon is enclosed in brackets. 



When latitude and local time were determined simultaneously by means of the great Altazi- 

 muth, the latitude is generally given to seconds of arc, the clock correction to seconds of time, 

 and the longitude to minutes of arc or sometimes half minutes. When two pairs of stars were 

 observed, the degree of reliability may be inferred from the concordance of the numbers. For 

 observations with the Sextant or the small Altazimuth, the latitude is generally given to the 

 nearest minute or tenth of a minute. 



When only one of the two elements was determined at a time, as was always the case 

 in summer, the assumed value of the other, as used for the computation, is enclosed in square 

 brackets. In this case there is also added a column of differential coefficients, containing either 



TT r -j-i where dy> is the increment of latitude corresponding to an increment dt of hour angle 



(or clock correction or east longitude). In order to have the change of clock correction, corres- 

 ponding to a given change of latitude, expressed at once in seconds of time, when the change 

 of latitude is given in seconds of arc, the differential coefficient in the last case is given in the 



form A f 

 a<f> 



For the observations taken at sea, these differential coefficients do not always correspond 

 exactly to the coordinates here given, as they have in many cases already been used for the 

 correction of preliminary values. 



When observations of the Sun have been treated in the same manner as observations of 

 two stars, the result will be found between the lines containing the times of observation. 



