466 



Notices respecting New Booh. 



for the eleventh year, and compare the calculated times of high water 

 with the observed times, they will not be affected with any constant 

 error, but if we calculate for the tivenlij-fiist year the calculated times 

 will have a constant error of 10 minutes. Similar remarks apply to 

 the heights, that is, to the constant D. If the channel becomes 

 deeper, the tide-wave travels with greater velocity, and the high 

 water happens sooner. Thus again an indication arises which may 

 hereafter be useful to the geologist." — lb. p. vi. 



" The practice which at present obtains of referring the heights 

 of buildings and mountains to the level of the sea or to high or loio 

 water mark, seems objectionable. The heights of spring or neap 

 tides, although not subject to so much uncertainty, are also quanti- 

 ties too vague to be used with propriety as standards of reference." 

 —p. 24. 



"The establishment of London («'. e, the interval between moon's 

 transit F at 0*^ 0" and the time of high water) appears now to be very 

 different from what it was in the time of Flamsteed. It seems to 

 have fluctuated more than ten minutes even since the commence- 

 ment of this century. At the London Docks, in 1807, itwas2''0"9'"; 

 in 1818, 1^57-0"'; 'in 1835, 2''4-4"\— See Phil. Trans. 1837, p. 136, 

 and the accompanying plate. These numbers were obtained by Mr. 

 E. Russell, and the corrections requisite in order that they might 

 refer to the same parallax and declinations were carefully applied. 



" This perplexing fluctuation presents an insuperable obstacle to 

 extreme accuracy in tide predictions, until it can be explained. It 

 is probably owing to changes in the bed of the river, the drainage of 

 the banks, &c., which it is impossible to embrace in any mathema- 

 tical formula. Perhaps the manner of taking the observations may 

 have varied slightly. 



"I am indebted to Mr. Yates for notice of a very ancient tide 

 table which exists in a MS. in the British Museum. It is in the 

 Codex Cottonianus, Julius DVII., Avhich appears to have been M'rit- 

 ten in the 13th century, and to have belonged to St. Alban's Abbey, 

 It contains calendar and other astronomical or geographical matters, 

 some of which are the productions of John Wallingford, who died 

 Abbot of St. Albans, a.d. 1213. At p. 45 b. is a table on one leaf, 

 showing the time of high water at London Bridge, ' flod at london 

 brigge', thus : 



^tas 



Lunse. 



N. B. The numbers increase by 

 a constant difference of forty- eight 

 minutes. The first column gives 

 the moon's age in days. 



