376 Royal Society : — 



to the ordinary ocean temperature in the same latitude ; together 

 with the variations in all these respects which currents experience 

 in different parts of the year, and in different parts of their course. 

 As the information on these points, which may be expected to follow 

 from the measures adopted by the Board of 'IVade, must necessarily 

 depend in great degree on the intelligence, as well as the interest 

 taken in them by the observers, it is desirable that the instructions 

 to be supplied with the meteorological instruments should contain a 

 brief summary of what is already known in regard to the principal 

 oceanic currents ; accom])anied by charts on which their supposed 

 limits in different seasons, and the variations in those limits which 

 may have been observed in particular years, may be indicated, with 

 notices of the particularities of the temperature of the surface-water 

 by which the presence of the current may be recognized. Forms 

 will also be required for use in such localities, in which the surface 

 temperatures may be recorded at hourly or half-liourly intervals, 

 with the corresponding geographical positions of the ship, as they 

 may be best inferred from observation and reckoning. For sucli 

 localities also it will be necessary that the tables, into which the 

 observations of different ships at different seasons are collected, 

 should have their bounding lines of latitude and longitude brought 

 nearer together than may be required for the ocean at large. 



In looking forward to the results which are likely to be obtained 

 by the contemplated marine observations, it is reasonable that those 

 which may bear jjractically on the interests of navigation should 

 occupy the first jjlace ; but, on the other hand, it would not be 

 easy to over-estimate the advantages to physical geography, of 

 geiieral tables of the surface temperature of the ocean in the dif- 

 ferent months of the year, exhibiting, as they would do, its normal 

 and its abnormal states, the mean temperature of the different 

 parallels, and the deviations therefrom, whether permanent, peri- 

 odical, or occasional. The knowledge which such tables would 

 convey is essentially required for the study of climatology as a 

 science. 



The degree in which climatic variations extending over large 

 portions of the earth's surface may be influenced by the variable 

 phenomena of oceanic currents in different years, may perhaps be 

 illustrated by circumstances of known occurrence in the vicinity 

 of our own coasts. The admirable researches of Major Ilennell 

 have shown that in ordinary years, the warm water of the great 

 current known by the name of the Gulf-stream is not found to the 

 cast of the meridian of the Azores ; the sea being of ordinary ocean 

 temperature for its latitude at all seasons and in every direction, in 

 the great space comprised between the Azores, and the coasts of 

 Europe and North Africa : but Major Rennell has also shown that 

 on two occasions, viz. in 1776 and in 1821-1822, the warm water by 

 which the Gulf-stream is characterised throughout its whole course 

 {being several deyrees above the ordinary ocean temperature in the 

 same latitude), was found to extend across this great expanse of 

 ocean, and in 177G (in particular) was traced (by Dr. Franklin) 



