Royal Society. 357 



of Atmospheric Electricity." By Alexander Barry, Esq. F.L.S. 

 Communicated by J. G. Children, Esq. Sec.R. S. 



A kite was raised in an atmosphere which appeared favourable to 

 the exhibition of electrical phenomena, from an apparatus firmly 

 fixed in the earth, and insulated by a glass pillar. The string to 

 which it was affixed contained a double gilt thread, and was let out 

 to a length of five hundred yards. It was connected with a platina 

 tube passing about half way down a glass tube full of a solution of 

 sulphate of soda, coloured with syrup of violets, and inverted in a 

 cup containing the same liquid. A similar wire in another tube, also 

 filled with the coloured solution, was placed in communication with 

 the earth, and the fluids in each made to communicate by a bent 

 glass tube passing from one cup to the other. The result of the 

 experiment was, that hydrogen gas and alkali were developed in the 

 first tube, and oxygen gas and acid in the latter. 



The reading of a Paper, entitled, " An Account of Operations 

 carried on for ascertaining the Difference of Level between the River 

 Thames at London Bridge and the Sea : and also for determining the 

 Height above the Level of the Sea, &c. of intermediate points passed 

 over between Sheerness and London Bridge." By John Augustus 

 Lloyd, Esq. F.R.S. ; was commenced. 



Mar. 3. The reading of Mr. Lloyd's Paper was resumed and 

 concluded. 



The author of this paper received directions from the Lords Com- 

 missioners of the Admiralty, in February 1830, at the suggestion 

 of the Royal Society, to survey the river Thames, with a view of 

 ascertaining the difference of level between certain parts of it and 

 the mean level of the sea near Sheerness. Having had experience, 

 while employed in a survey of the Isthmus of Darien, of the great 

 imperfections in the levelling instruments hitherto used, he bestowed 

 great pains in improving the construction of those employed in the 

 present survey ; endeavouring to combine the properties of great 

 steadiness and accuracy of motions in azimuth, with increased deli- 

 cacy in the level, and permanence in the general position of the 

 whole apparatus ; and also to increase the power of the telescope. 

 The author then enters into a full description of the improved in- 

 struments which he employed, accompanied by drawings. 



As soon as he was furnished with the proper means of observing, 

 he commenced his operations at Sheerness in the month of March. 

 The principal object of his commission being to ascertain the heights 

 of different places above the level of the sea, it became necessary, 

 in the first place, to estimate the heights of the tide ; and accord- 

 ingly having obtained permission from the Admiralty to erect a tide 

 guage at the Dock Yard at Sheerness, he selected a corner of the 

 boat basin as the most eligible spot for this purpose : having accom- 

 plished this object, he next directed his attention to the establish- 

 ment of a standard mark, from whence, as from a zero point, the 

 levellings might be reckoned. Considerable difficulty was met with 

 in fixing upon a spot in every respect adapted to this object ; for 

 all the buildings in the immediate vicinity of the tide gauge appeared 



to 



