Imagens das páginas



The institution of a system of corresponding observations, organised, in 1829, by Humboldt and Kupffer for the advancement of the science of terrestrial magnetism, and the example which was set by Gauss in the establishment of fixed observatories on the Continent, was soon followed by the English government, which, at the instigation of the British Association, granted the necessary sums of money for the erection of magnetic stations throughout the British Empire.

The Royal Society, which was deeply interested in the undertaking, imparted, through the able exertions and the ingenuity of Professor H. Lloyd of Dublin and Lieutenant-Colonel Sabine, a character of superiority, to all the established observatories which the magnetic continental stations could not boast of; as, to the arrangements for a strict simultaneity in taking the observations, was joined an exact similarity of instruments and a uniform method of observing.

The superiority of this plan was recognised by the accession of 22 continental observatories to the compact which governed those of Great Britain; and, as a striking and characteristic feature of the advance and results of civilisation, it may be here mentioned that this accession formed a scientific league, in which the governments of Great Britain, France, Austria, Russia, Prussia, Belgium, Spain, Bavaria, the United States, the Pacha of Egypt, the Rajah of Travancore, and the King of Oude were all peaceably united in the common interest of promoting the science of terrestrial magnetism.*

Great Britain numbers in that league twelve magnetic stations, viz. those of Greenwich, Cambridge, Dublin, Kelso (the private one of Sir Thomas Brisbane), Simla, Madras, Singapore, Bombay, Toronto, St. Helena, Cape of Good Hope, and Van Diemen's Land.

The last of these observatories was established in Hobart Town towards the end of 1840, by the intrepid navigator, Sir James Ross, then bound on an expedition to the South Pole. It was fitted up by him with the best instruments for magnetic, astronomical, and meteorological observations; and was left under the direction of Lieutenant Kay of the " Terror," a zealous, accurate, and intelligent observer, and under the protection of Sir John Franklin, then Governor of Van Diemen's Land, a friend and promoter of science, and who, to his valuable services in effecting the prompt erection of the required observatory, joined a readiness to assist the observers with his own experience and his personal co-operation.

The establishment of that observatory with the object of obtaining all the elements which were needed from that part of the world for elucidating the general question of the earth's magnetic force, has rendered the detached, unconnected, and minor observations of occasional observers of little or no value.

Amongst these, the writer classes his own labours, which he had commenced and pursued while sepa

• "Account of the Magnetical Observatory of Dublin, and of the Instruments and Methods of Observation employed there," by the Rev. Humphrey Lloyd, D.D. Dublin, 1842.

[ocr errors]

rated from communication with the scientific world, ignorant of the association that had been formed, and which, although extensive, have, since he has examined and tested them by the standard of the present knowledge, possessed upon the subject, procured for him only the' mortifying consciousness that the time which they took in making, might have been more profitably employed, and the cost of the instruments which they required, more usefully invested.

Independently of the circumstance of their being unconnected, the value of these observations is also greatly impaired by their having been made beyond the precincts of an observatory. Indeed, to any one who has the slightest idea of the nature of the observations alluded to; of the nicety and delicacy of the requisite instruments; of the accuracy with which they require to be mounted and handled; of the minute precautions which are necessary to insure successful results; and on the other hand, of the interference of external circumstances which a pedestrian explorer in the writer's situation has to encounter, such as the carelessness and clumsiness of the men who carry the instruments, the imperceptible dust which floats in the atmosphere, the effects of wind, heat, rain, and moisture, and of local attraction variously disseminated, and of various intensities, and against all of which a tent offers a very insufficient protection; to those familiar with these annoyances, the difficulties in securing good observations will be at once apparent.

The writer, then, anxious not to extend unnecessarily the pages of this volume, will limit himself to the noticing only of that element of Terrestrial Magnetism called declination or variation, and which, made under more favourable circumstances, furnishes a result which may be depended on, and which, if applied to the question of the land surveys conducted ac


cording to the magnetic meridian, may be of some value.





The main object of my visit to New South Wales was to examine its mineralogy.

The excursions undertaken with a view to that object, led me through a very wild and broken country, often difficult of access, rarely permitting a rapid progress, or affording compensation for no slight degree of labour, fatigue, and privation. Indeed, the scarcity of simple minerals was such as might have discouraged the most ardent and persevering mineralogist who ever devoted himself to the science. But, although the scope for extensive mineralogical researches was thus narrowed, the country was soon found to present a vast field for a most exciting and interesting geological investigation. Viewed through the medium of Geology, it at once assumed the aspect of an historical ground, where, in the absence of monuments and records of human generations, nature unfolds annals of wonders; not indeed, that they can be so called, as furnishing new lights thrown upon the origin of things, but as yielding additional evidence that the structure to which they relate is analogous to that of the rest of the globe.

I entered therefore eagerly on a geological examination of New South Wales, as on a terra incognita, without guide or guide-book, as I had not the good

« AnteriorContinuar »