No. (4.)
To his Excellency Signor Bianchini, Minister of the Interior, &c., Kingdom of Naples.
Mon Signore,
It is an object of high importance to the advancement of terrestrial physics, to determine with rigid accuracy, the extent of elevation or of depression, which large tracts of land are thought to undergo, when, as in the kingdom of Naples, exposed to volcanic influences from beneath. Nowhere in Europe, do circumstances so favourable for such observation, and so precious to science, exist, as around Naples and especially at the Temple of Serapis, already the subject of much investigation in this respect. Unfortunately, however, nearly all determinations of level hitherto attempted in this region, are comparatively valueless, because the only fixed datum possible, as that whereby changes of level in the land should be determined, has been the assumed mean level of the tide, in the Bay of Naples. But from the very small rise and fall of the tides here, and the great perturbations to which they are liable from changes of direction and force of wind, &c., such affords no certain fixed datum whatever, from which to measure changes of level.
To establish, therefore, in their stead, a fixed datum, which should become the standard to which hereafter all scientific levels could be referred, (and to which, also, all levels of public works might be referred, if thought proper by Government,) would be a work, at once worthy of his Majesty the King, highly promotive of European science, and valuable hereafter, even for civil purposes, within the kingdom of Naples.
