bf the Place of Ob^ervatio77. 4ih 



v.eather did not continue sufficiently long for this purpose; 

 nor has an opportunity offered since the pe'iod at which 

 these ohservations were made to repeat ihcni. The sets 

 were four in number; two were taken on the 25th of Oc- 

 t()!)er, and the r<:'inainiiig; two on the 97th. The sun's and 

 moon's altitude were taken from an artificial horizon, and 

 the time at each observation noticed from a common iiori- 

 zontal walch showing seconds : great accuracy was not 

 regarded in taking the moon's altitude, nor indeed of the 

 sun's, except that set from whence the time was to be 

 computed, for a small error in the observed altitude cannot 

 materially afit-ct the correction to be applied in reducing 

 ihe apparent to the true distance : great care however 

 should be observed in noticing the moitient when the di- 

 stance is completed, as, whatever error is committed here, 

 will appear in the longitude, that being deduced by a com- 

 parison of the time at Greenwich, given by the observed 

 distance compared with the distance deduced from the 

 Nautical Almanac, and the lime inferred from the sun's 

 otxerved altitude. 



The method which t should advise would be, fir*t, to 

 take a sinclc observation of the altitude of the moon's en- 

 lightened limb, then one of the sun's lower limb*, and when 

 these have been completed, take with the greatest care five 

 distances at least ot the proper limbs of the sun and moon. 

 ^'V^hen these are finished, take another altitude of the sun, 

 then one of the moon ; these four altitudes of the sun and 

 uioon will be sufficient fur cleannij:: the distance: and if 

 thty are taken at nearly equal intervals of time before and 

 after the time at distance, it will be only necessary to take 

 a mean of each two corresponding altitudes, which \vill 

 very nearly correspond to the apparent altitudes when the 

 distance was taken ; but a set of observations of the alti- 

 tude of the proper liiTib of the sun should now be taken, 

 and the time noted down with the greatest care. These 

 observations should not be less than tive, because from 

 tliem the apparent time at distance is to be inferred by a 

 com|)aris()n with the watch. From this method of proceed- 

 ing little difficulty occurs, or additional trouble to the usual 

 nuthod by three separate observers ; and 1 am induced to 

 think that it possesses many advantages over that method 

 in point of accuracy, for in the latter case the whole is com-i 



• 1 liii applies equally to a Kar wjien that U ii«cd instead of the 3un,and i» 

 to be ku uiideritoud iu all caiu« licre rclcrrcd to. 



plclcd 



