ON THE MEASUREMENT OP THE LUNAR DISTURBANCE OF GRAVITY. 115 



there was a candidate in philosophy and theology named Lorenz Hengler, 

 of Reichenhofen, ' der weder friiher noch spater zu finden ist.' 



At p. 150 of the same volume Professor Safarik contributes a 'Bei- 

 trag zur Geschichte des Horizontalpendels.' He says that the instru- 

 ment takes its origin from Professor Gruithuisen, of Munich, whose 

 name has ' keinen guten Klang ' in the exact sciences. 



This strange person, amongst other eccentricities, proposed to dig a 

 hole quite through the earth, and proposes a catachthonic observatory. 

 Gruithuisen says, in his ' Neuen Analekten fiir Brd- und Himmelskunde ' 

 (Munich, 1832), vol. 1, part i. : ' I believe that the oscillating-balance 

 (Schwung-wage) of a pupil of mine (named Hengeller), when constructed 

 on a large scale, will do the best service.' 



Some of the most interesting observations which have been made 

 are those of M. d'Abbadie. He gave an account of his experiments in a 

 paper, entitled ' fitudes sur la verticale,' ' Association Fran9aise pour 

 I'avancement des Sciences, Congres de Bordeaux, 1872,' p. 159. As this 

 work is not very easily accessible to English readers, and as the paper 

 itself has much interest, we give a somewhat full abstract of it. He has 

 also published two short notes with reference to M. Plantamour's obser- 

 vations (noticed below), in vol. 86, p. 1528 (1878), and vol. 89, p. 1016 

 (1879), of the ' Comptes Rendus.' We shall incorporate the substance of 

 his remarks in these notes in our account of the original paper. 



When at Olinda, in Brazil, in 1837, M. d'Abbadie noticed the varia- 

 tions of a delicate level which took place from day to day. At the end of 

 the two months of his stay there the changes in the E. and W. azimuth 

 had compensated themselves, and the level was in the same condition as 

 at first ; but the change in the meridian was still progressing when he 

 had to leave. 



In 1842, at Gondar, in Ethiopia, and at Saqa, he noticed a similar 

 thing. In 1852 he gave an account to the French Academy (' Comptes 

 Rendus,' May, p. 712) of these observations, as well as of others, by 

 means of levels, which were carried out in a cellar in the old castle of 

 Audaux, Basses Pyrenees. 



Leverrier, he says, speaks of sudden changes taking place in the level 

 of astronomical instruments, apparently without cause. Airy has proved 

 that the azimuth of an instrument may change, and Hough notes, in 

 America, capricious changes of the Nadir. 



Henry has collected a series of levellings and azimuths observed at 

 Greenwich during ten years, and during eight of the same years at Cam- 

 bridge ('Monthly Notices, R.A.S.,' vol. 8, p. 134). The results with 

 respect to these two places present a general agreement, and show that 

 from March to September the western T of the transit instrument falls 

 through 2"-5, whilst it deviates at the same time 2" towards the north. 

 Elhs has made a comparison of curves applying to Greenwich, during 

 eight years, for level and azimuth. He shows that there is a general 

 correspondence with the curves of the external temperature (' Memoirs 

 of the R. Ast. Soc.,' vol. 29, pp. 45-57). 



In the later papers M. d'Abbadie says that M. Bouquet de la Grye 

 has observed similar disturbances of the vertical at Campbell Island, 

 lat. 52° 34' S.. M. Bouquet used a heavy pendulum governing a 

 vertical lever, by which the angle was multiplied.' He found that the 

 1 I do not find a reference to M. Bouquet in the K.S. Catalogue of _ scientific 

 papere. It appears from what M. d'Abbadie says that certain observations have 



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