146 



NATURE 



[August 4, 1910 



subsidence has gone on increasing in the last eighty 

 years, and this serious conclusion has attracted the 

 attention of competent authorities. 



The investigations of the Commission have clearly 

 brought out the following facts : — 



(ij The tower does not rest on a mass of masonry 

 extending over the whole area of the circular base, as 

 was hitherto supposed, but is supported only by a 

 more limited annulus of masonry corresponding to the 

 cylindrical form of the superstructure. 



{2) The foundations, hitherto supposed to be about 

 8 metres deep, are, on the contrary, much more super- 

 ficial, and hardly sink to 3'6o metres below the level 

 of tlie ground. 



(3) A spring of water rises at the junction of the 

 foundations with the surrounding permeable earth, 

 causing serious damage to the foundations them- 



selves. A tank excavated near the tower in 1839 for 

 th; purpose of maintaining the surrounding basin dry 

 and preserving the base in good condition was made 

 verv deep, and much below the level of the actual 

 edge, thus collecting other waters, which were pumped 

 out 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 the 

 first to the seventh tier, 86'5 mm. per metre of height. 

 The slope, as now determined by optical appliances by 

 Prof. Pizzetti, and directly by the plumb-line by the 

 engineers, Drs. Cuppari and Bernieri, is — again from 

 the first to the seventh tier — 92 mm. per metre. The 

 slope has therefore increased 5A mm. per metre, and 

 there 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 3'265 metres, exceeding that found by 

 the English observers in 1829 by nearly 20 centimetres. 



The Commission has not been able to decide 

 whether the increase in the leaning took place gradu- 

 ally or at intervals as the result of different causes. 

 One such cause might be the excavation of the tank 

 and the ill-advised pumping operations already men- 

 tioned ; another miglit be sought in the effects of the 

 earthquake of 1S46, which was fairly violent at Pisa, 

 and, as asserted by Leopoldo Pilla in his account 

 of the times, caused the tower to oscillate in an alarm- 

 ing way. "Those people who had the opportunity of 

 observing it during the shock," writes the great 

 geologist, '■ assure me that its swaying was a terrible 

 sight." 



In spite of these serious conclusions, the Commis- 

 sion is nevertheless unanimously of opinion that the 

 famous tower of Pisa still possesses good stability, 

 and that the present condition of the same is not 

 such as to give rise to excessive apprehension for the 

 future. 



A. Battelli. 



RECENT BOOKS ON BOTANY.' 

 (i)]\,TR. SCOTT ELLIOT has attempted an ambi- 

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 origin of the fern sporophyte, the reduction of the 

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 of individuality is applicable to plants. Unfortunately, 

 Mr. Elliot does not discuss the question, though he 

 brieflv refers to it again on p. 152. It is to be ex- 

 pected that some inaccuracies should creep into a book 

 of this nature. A desire for brevity is probably 

 responsible for the statement on p. 109 that the 



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