ADDRESS OF THE PRESIDENT OF THE BRITISH ASSOCIATION". 



1832.] 



chemists now living have undertaken extensive and laborious, 

 though isolated researches ujjon the combining quantities of some 

 of the most important elements. But much more than has been 

 already performed still remains undone. Such a subject, it is 

 believed, might be highly proper for consideration by the Chemical 

 Section ; to whose notice it would be introduced by the distin- 

 guished chemist, Dr. Andrews, who presides over that Section, — 

 and than whom no one could be named as more competent to 

 estimate the importance of such a revision, or to judge more truly 

 of the qualifications that would be required for its execution. 



The theory of Heat has made great advances within the last 

 ten years. Mr. Joule has by his experiments confirmed and 

 illustrated the views demonstrated about the end of the last cen- 

 tury by Davy and Rumford regarding the nature of heat, which 

 are now beginning to find general acceptance. He has deter- 

 mined with much accuracy the numerical relation between 

 quantities of heat and mechanical work. He has pointed out 

 the true principles upon which the mechanical value of any 

 chemical change is to be estimated, and by very careful experi- 

 ments he has arrived at numerous expressions for the mechanical 

 equivalents in some of the most important cases of chemical action 

 in galvanic batteries, and in combustion. These researches appear 

 to be laying the ground-woi'k for the ultimate formation of a 

 Mechanical Theory of Chemistry, by ascertaining experimentally 

 the mechanical equivalents expressed in absolute motive force of 

 the thermic, electric, and magnetic forces. 



In connexion with the subject of heat, I would advert to the 

 experiments in which Mr. Hojskins is engaged for investigating 

 the possible influence of high pressure on the temperature at 

 which substances in a state of fusion solidify — an inquiry which 

 was shown by Mr. Hopkins, in a report recently presented to the 

 British Association, to have an important bearing on the questions 

 of the original and present state of the interior of the earth. It 

 is well known that the temperature of the earth increases as we 

 descend, and it has been calculated that at the rate at which the 

 increase takes place in such depths as are accessible to us, the 

 heat at a depth of 80 or 100 miles would be such as to fuse most 

 of the materials which form the solid crust of the globe. On the 

 hypothesis of original fluidity, and assuming that the rate of 

 increase known to us by observation continues farther down, and 

 is not counterbalanced by a considerable increase in the 

 temperature of fusion occasioned by pressure, the present state 

 of the earth would be that of a solid crust of 80 or 100 

 miles in thickness enveloping a fluid nucleus. Mr. Hopkins 

 considers this state to be inconsistent with the observed amount 

 of the precession of the equinoxes, and infers that if the temper- 

 ature of fusion be not increased considerably by pressure, the 

 hypothesis of internal high temperature being due to primitive 

 heat cannot be corre;t; whilst, on the other hand, if the temper- 

 ature of fusion be considerably heightened by pressure, he con- 

 siders the conclusion to be unavoidable, that the earth must be 

 solid at the centre. 



Mr. Hopkins is assisted in these experiments, which are carried 

 on at Manchester, by the well-known engineering knowledge of 

 Mr. Fairbairn, and the equally well-known experimental skill of 

 Mr. Joule The principal difficulties attending the experiments 

 with substances of low temperatures of fusion have been over- 

 come, and strong hopes are entertained of success with substances 

 of more difficult fusibility. The pressures employed are from 

 three to four tons to eight and ten tons on the square inch. The 

 latter is probably equal to the pressure at several miles beneath 

 the earth's surface. 



From Heat the transition is eas}', and by many may be deemed 

 natural, to Terrestrial Magnetism, — a science which perhaps 



83 



more than any other has profited by the impulse and systematic 

 direction communicated to it by the British Association, and 

 which perhaps more than any other required such external aid. 



We recognize in terrestrial magnetism the existence of a power 

 present everywhere at the surface of our globe, and producing 

 everywhere eflects indicative of a systematic action ; but of the 

 nature of this powei-, the character of its laws, and its economy 

 in creation, we have as yet scarcely any knowledge. The appa- 

 rent complexity of the phenomena at their first aspect may 

 reasonably be ascribed to our ignorance of their laws, which we 

 shall doubtless find, as we advance in knowledge, to possess the 

 same remarkable character of simplicity which calls forth our 

 admiration in the laws of molecular attraction. It has been 

 frequently surmised, — and the anticipation is, I believe, a strictly 

 philosophical one, — that a power whicli, so far as we have the 

 means of judging, prevails everywhere in our own planet, may 

 also prevail in other bodies of our system, and might become 

 sensible to us — in the case of the sun and moon particularly — by 

 small perturbing influences measurable b}' our instruments, and 

 indicating their respective sources by their periods and their epochs. 

 As yet we kuow of neither argument nor fact to invalidate this 

 anticipation ; but, on the contrary, much to invest it with a high 

 degree of pi'obability. Be this, however, as it may, we have in 

 our own planet an exemplification of the phenomena which 

 magnetism presents in one of the bodies of our system, on a 

 scale of sufficient magnitude, and otherwise convenient for our 

 study. Accordingly, the first object to which the British Asso- 

 ciation gave its attention was, to obtain a correct knowledge of 

 the direction and amount of the magnetic force generallj" over 

 the whole surface of the globe corresponding to a definite epoch. 

 It has been customary to represent the results of magnetic obser- 

 vations by three S3'stems of Lines, usually called isogonic, isoclinal, 

 and isodynamie lines. (Lines of equal horizontal direction, of 

 equal vertical direction, and of equal force.) In the maps of 

 these lines existing in 1838, large spaces of the earth's surface 

 were either blank, or the lines passing across them were very 

 imperfectly supported by observations. In the more frequented 

 parts, where obser\'ations were more numerous, the discrepancies 

 of their dates impaired their suitability for combination ; for the 

 position and configuration of the magnetic lines have been found 

 to undergo a continual process of systematic change, with the 

 causes of which we are as 3-et wholly unacquainted, but which 

 has obtained the name of secular change, to distinguish it from 

 periodical vaiiations of known and limited duration. Amongst 

 the most marked deficiencies in these maps, were the greater part 

 of the extra-tropical portion of the southern hemisphere, — the 

 British possessions in North America, and British India; — mag- 

 netic surveys of these were expressly recommended, and the 

 practicabihty and advantage of making the observations on board 

 ship, and of thus extending them over the surface of the ocean, 

 were pointed out. It is most pleasing to recall to recollection, 

 and gratifying to acknowledge from this chair, the favourable 

 manner in which the recommendations of the British Association 

 were received by Her Majesty's Government and by the East 

 India Company, and how promptly and effectually they ha\e 

 been carried out. The blanks in the southern hemisphere have 

 been filled up by maritime Expeditions appointed expressly for 

 the purpose. Magnetic surveys have been completed of British 

 North America at the ex-pense of our own Government, — and of 

 the Indian Archipelago at that of the East India Company, — 

 and India itself is now in progress ; whilst owing to the zeal of 

 our naval officei-s, contributions have flowed in from almost every 

 accessible part of the ocean. The co-ordination and mutual 

 connexion of so large a mass of materials is necessarily a work 

 of time, but is progressing steadilj' towards completion, and when 

 presented in one connected view, will fonn the groundwork on 

 which will securely rest a " general theory of ten-estrial magnet- 



