354 



once their changing positions with the changing seasons. Twelve 

 other small maps of subnormal lines show, in like manner, for each 

 month, the difference between the actual mean temperature for that 

 month, and the normal temperature (that due to the latitude) at all 

 places situated along each abnormal line. These, with other subsi- 

 diary maps, present to us at once, and with the greatest perspicuity, 

 the principal results of these laborious investigations. 



These maps are accompanied by a considerable quantity of letter- 

 press, containing not only descriptive details, but also a very able 

 discussion of some of the principal results obtained, and of the 

 general conclusions deducible from them; more especially as regards 

 the causes of the abnormal temperatures which characterise the 

 northern hemisphere. The influence of oceanic currents, on the 

 temperature of the regions in w^hich they prevail, was very inade- 

 quately appreciated before the publication of these researches. Of 

 these currents, the most important, and infinitely the most interesting 

 to ourselves, is that so well known as the Gulf-stream. Its immense 

 influence in moderating the winter cold along the shores of western 

 Europe is shown by the singularly abnormal position of the winter 

 isothermals in that region; and not only is this fact of great interest 

 in itself, and of first-rate importance in meteorology, but it has also 

 enabled the geologist to form a far more accurate estimate than 

 otherwise it would have been possible to have done, of the probable 

 climatal influences of particular configurations of land and sea, and 

 thus to overcome, not by arbitrary hypothesis, but by logical 

 deduction, some of the greatest apparent anomalies in speculative 

 geology. The former existence of glaciers in our own islands need 

 no longer be regarded as a mystery, for it is now demonstrable that 

 they would be the highly probable, if not the absolutely necessary 

 consequences of any configuration of land and sea which should 

 divert the Gulf- stream from its present course ; and the geologist 

 has no difiiculty in conceiving such a configuration, not merely as a 

 possible, but as one which probably did exist during the glacial period. 

 I mention this as an instance of the diffusive influence of a great 

 step in one science, on the progress of other sciences more or less 

 directly associated with it. A further and very important conclusion 

 has been deduced by Professor Dove from the monthly isothermals, 

 I mean the fact that the mean temperature of the surface of the 

 globe, as a whole, is higher when the sun is in the northern, than 

 in the southern signs. The explanation is, that the northern hemi- 

 sphere has more land than sea at the surface, and the southern much 

 more sea than land, and that from the different action of the sun's 

 rays on the solid and fluid surfaces, it follow^s that the hot summer 

 of the northern hemisphere added to the mild winter of the southern, 

 gives a mean of general temperature several degrees of Fahrenheit 

 higher than the cool summer of the southern, together with the 

 cold winter of the northern hemisphere. 



It will, I doubt not, be generally felt by all who are acquainted 

 with these researches, that Professor Dove has well merited the 

 honour which the Council has conferred upon him in this award of 

 the Copley Medal. 



