VOL. XXXV 



tl.] 



PHILOSOPHICAL TRANSACTIONS. 



east, a fresh gale, by the wooden instrument forwards. The watch, by the 

 mean of the observations, appeared to be about 8*" 45^ too slow ; tlie visible 

 horizon being supposed 3' 30" depressed below the true, by the height of the 

 observer's eye above the surface of the water, aiiiounling to about 8 or 9 feet. 



The following altitudes of the sun were observed Sept. ] , before noon, under 

 sail from Sheerness towards the Spile-Sand, with the tide of ebb, the wind blow- 

 ing hard at north east, by the wooden instrument forward. The second spe- 

 culum being removed by some accident from its due position, so as to increase 

 the angles observed about ]° 3-^', as appeared by the first observations of the 

 afternoon of the same day, made with the same instrument, in the same man- 

 ner, while they continued lying-by near the Spile; which 1° 3i' are added to 

 the errors of the divisions of the instrument in the /th column. While these 

 observations were making, the yacht steered at first chiefly east, sometimes 

 south east, afterwards stood to the north-east, towards the Swin. The time 

 of the watch was regulated by some of the later observations made when they 

 were most eastward, and this was probably the cause why the first altitudes 

 which were taken, while they were more westerly, fall so much short of the 

 computations, the difference decreasing gradually as they advanced towards the 

 east. 



