l-iG Dr Pearson, On a new kind of self-acting weir. [Feb. 25 



the windlass, if the water be nearly level, will be about 25 lbs. ; 

 if there be a fall of about 2 ft., as will possibly be the case, if there 

 be much stream and a large proportion of the valves are already 

 raised, it may be doubled, but not much more. The tension on 

 the chain in the first case will be about 84 lbs. and increase pro- 

 portionately as the water rises. 



I am much indebted to W. M. Fawcett, Esq., for permitting the 

 sketches given in the annexed plate, and also those exhibited to 

 the Society, to be drawn in his office. But much more perfect 

 plans including the dimensions and all other details, will be found 

 in the volumes to which I have already referred, viz. : 

 ^heAnnales des Fonts et Chaassees, 1839, Memoires, vol. 2, p. 238, 

 „ ■ „ „ 1861, „_ p. 209, (for 



the mathematical investigation.) 

 „ „ „ 1866, Memoires, p. 172, 



1873, „ p. 198. 



I may add that though the technical terms employed are a 

 little puzzling to one not a professional engineer, I have found no 

 difficulty, with the aid of M. Littrd's Dictionary, in interpreting 

 them satisfactorily. 



"With the exception of a few remarks made by Major Trench, 

 R.E., M.P., in the last Parliament, I think in the year 1873, in a 

 debate on some proposed improvements in the Shannon, I do not 

 recollect having seen any reference in any English publication to 

 the system described in this paper : nor does it seem to have been 

 discussed, where it might most naturally have been expected, 

 in the Proceedings of the Institution of Civil Engineers. It is 

 right to mention this, in presenting a communication on a subject 

 with which I cannot claim to have a technical acquaintance. 



P.S. Juli/ 18. — On examining the weir at Port a I'Anglais in 

 June, I observed that the chevalets hinge within the hausses, or 

 valves ; and are actually beneath them, so that there is nothing 

 intervening between each pair. Otherwise, I think my description 

 is quite exact in all important details. 



(2) " On a manuscript Table of Napierian Log. Sines, d&c." 



Dr Pearson also exhibited to the Society a MS. volume, 

 belonging to Emmanuel College, containing Tables of Natural 

 and Logarithmic Sines, &c., &c. It is incomplete, and from 

 the name written at the beginning, seems to have belonged 

 originally to Mr Thomas Leigh (or Lee), a well-known schoolmaster 

 at Bishop Stortford, during the latter part of the seventeenth cen- 

 turyS A complete specimen of the tables, viz., 5**. 0' to 5°. 5' and 



1 Mr Lee seems to have graduated as B. A. at Oxford, in 1641 ; but in 1646 lie in- 

 corporated at Emmanuel, became a Fellow and took his M.A. degree. In 1663 he 



