156 THE VOYAGE OF H.M.S. CHALLENGER. 



the observed latitude being 36° 23' 30" N. At 10.20 a.m. a set of sights was obtained, 

 and as the bearing of the sun at that time made it a matter of importance to know 

 exactly the latitude (an error of one mile of latitude causing an error of one mile in longi- 

 tude), the result given by the observations then taken furnishes a very good test of the 

 accuracy of the deductions. The interval from noon being 1*7 hour, it follows that 

 the position of the ship at the moment, calculated by the known rate of the current 

 from the noon results, will be lat. 36° 20' 48" N., long. 71° 51' 44" W., and the 

 longitude, calculated from the observations, was 71° 53' 45" W. Again, at 8.40 a.m. the 

 position calculated from the noon observation was lat. 36° ] 8' 15" N., long. 71° 57' 6" W., 

 and longitude calculated from the observations at the time was 71° 57' 30" W. 

 Such an accordance between the calculated positions and those obtained by observation 

 will, in all probability, be deemed a sufficient proof, together with the fact of the rate 

 at which it was necessary to steam to keep the sounding line perpendicular, that this 

 estimate of the strength and direction of the Gulf Stream whilst the vessel was in it 

 is a very close approximation to the truth. 



At 5 p.m., these observations being completed, the ship proceeded N.N.W. (N. 30° W. 

 true) at right angles to^ the direction of the stream. At 9.30 p.m. the surface temperature 

 had fallen from 75°'0 to 69 o, 0, and the patent log showed that the vessel had gone 10 miles 

 through the water. At 11 p.m. the surface temperature was 67° "5, but at midnight it 

 had fallen to 56°'5, and continued nearly the same the whole of the next day. 



On the 2nd and 3rd May the weather was so thick with rain and fog that no 

 observations of any of the heavenly bodies could be obtained. On the 4th May the clouds 

 cleared off, and it was possible to ascertain the position of the ship at 6 a.m., which proved 

 to be lat. 39° 5'N., long. 71° 55' W., the position by D.R. at this time being 38° 57' N., 

 71° 57' W., that is allowing for a current of 3^ miles per hour up to 9.30 p.m. on the 1st, 

 at which time the temperature decreased 6°. It will, therefore, be seen that the position 

 by D.R. was 8 miles south of that by observation — a difference due, in all probability, to 

 an error in the leeway allowed from 2 p.m. on the 3rd to 6 A.M. on the 4th, during which 

 time the ship was close hauled ; previously the course had been off the wind. 



Recapitulating, then, it appears that on May 1st, at 6 a.m., the temperature of the 

 surface water rose to 75° - 0, and that at 6.40 a.m., when soundings, &c, were taken, and 

 when the ship had run 5 miles to N.N.W. from 6 A.M., her position by D.R. and observa- 

 tion showed a difference of but 4 miles in longitude ; that by astronomical observation 

 the ship drifted between 6.40 a.m and 4.30 p.m. 3^ miles per hour in a N. 60° E. 

 direction (true), the temperature of the surface water remaining at 75° ; that from 5 p.m. 

 to 9.30 p.m. the ship proceeded in a N. 30° W. direction (true) for 10 miles, the surface 

 temperature still remaining at 75 o, 0, but that immediately afterwards it fell to 69° - 0, and 

 was at midnight 56°"5 ; and that allowing a current of 3^ miles per hour N. 60° E. (true) 

 during the time the surface temperature remained at 75° # 0, the longitude by D.R. agrees 



