. Nature . nd-Hansen and Nansens Nor-wegian Sea. Report on Norwegian Fishery, vol. ii , 1909, No. 2, p. 107 ;and Miss Kirstine Smiths Gezeitenstroemern, Havenundersogelser, , No. 13, igio. 146 NATURE [August 4, 1910 subsidence has gone on increasing in the last eightyyears, and this serious conclusion has attracted theattention of competent authorities. The investigations of the Commission have clearlybrought out the following facts :— (ij The tower does not rest on a mass of masonryextending over the whole area of the circular base, aswas hitherto supposed, but is supported only by amo
. Nature . nd-Hansen and Nansens Nor-wegian Sea. Report on Norwegian Fishery, vol. ii , 1909, No. 2, p. 107 ;and Miss Kirstine Smiths Gezeitenstroemern, Havenundersogelser, , No. 13, igio. 146 NATURE [August 4, 1910 subsidence has gone on increasing in the last eightyyears, and this serious conclusion has attracted theattention of competent authorities. The investigations of the Commission have clearlybrought out the following facts :— (ij The tower does not rest on a mass of masonryextending over the whole area of the circular base, aswas hitherto supposed, but is supported only by amore limited annulus of masonry corresponding to thecylindrical form of the superstructure. {2) The foundations, hitherto supposed to be about8 metres deep, are, on the contrary, much more super-ficial, and hardly sink to 36o metres below the levelof tlie ground. (3) A spring of water rises at the junction of thefoundations with the surrounding permeable earth,causing serious damage to the foundations them-. selves. A tank excavated near the tower in 1839 forth; purpose of maintaining the surrounding basin dryand preserving the base in good condition was madeverv deep, and much below the level of the actualedge, thus collecting other waters, which were pumpedout regardless of the safety of the tower. (4) The slope of the tower, according to the measure-ments made in 1829 by Messrs. Cresy and Taylor,which mav be regarded as correct, was, from thefirst to the seventh tier, 865 mm. per metre of slope, as now determined by optical appliances byProf. Pizzetti, and directly by the plumb-line by theengineers, Drs. Cuppari and Bernieri, is—again fromthe first to the seventh tier—92 mm. per metre. Theslope has therefore increased 5A mm. per metre, andthere is thus an external displacement of 2868 metres,and a total deviation of the axis, from the first to the NO. 2127, VOL. 84] seventh tier, of 3265 metres, exceeding that found bythe English observers in 1829 by nearly 20
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