and of certain Liquids on the Surface of Water, 377 



2. The object of his second memoir 4 is (I.) to furnish an 

 additional number of facts by observers of repute bearing on the 

 subject in hand (for which the author is in great measure in- 

 debted to the Royal Society's Catalogue of Scientific Papers), 

 (II.) to meet certain objections that have been advanced against 

 the theory, and (III.) to supply a few more experimental proofs. 



3. In noticing the more remote facts, which are for the most 

 part stated by Professor Van der Mensbrugghe in a very brief 

 form, I must on several occasions enlarge considerably, since my 

 own labours, begun so long ago as 1838, have in some cases 

 anticipated more recent results. Many of my experiments have 

 been already given in the two papers referred to above (see note l ), 

 so that in the present communication I shall endeavour as far as 

 possible to avoid repetition. 



4. And first as to the additional facts, omitting mere guesses, 

 such as that of San Martino 5 , who, in 1793, attributed the mo- 

 tions of camphor to electrical action, we come to Sir H. Davy 6 , 

 who, in 1802, noticed that fragments of acetate of potash (then 

 called acetite) move on the surface of water somewhat after the 

 manner of camphor. The more irregular fragments rotate most 

 quickly, whence it is concluded that the shifting of the centre of 

 gravity had something to do with the phenomena, while the 

 rectilinear movements were attributed to currents descending 

 from the salient points of each fragment and so producing on it 

 unequal pressures. 



5. Carradori, in 1805, noticed 7 that when a large drop of the 

 milky juice of a euphorbiaceous plant is placed on the surface 

 of water in a large vessel, a portion of the drop spreads, while 

 another portion descends in threads which accumulate at the 

 bottom. If, then, the vessel be inclined so as to spill some of the 

 water and so renew the surface, on returning the vessel to its 

 first position the agitation will cause some of the milky filaments 

 to rise to the surface, where they spread like the first portion. 



6. These and a multitude of other phenomena, as noticed in 

 my first Experimental Essay 8 , were attributed by Carradori to a 



* " Sur la Tension superficielle des Liquides considered au point de vue 

 de certains mouvements observes a leur surface/' second me'moire, extrait 

 du tome xxxvii. des Memoires Couronnes &c, publies par l'Acad. Roy. des 

 Sci. de Belgique, 1873. 



5 Nuovo Giorn. Enciclopedico d' Italia, Marzo 1793. 



6 Journal of the Royal Institution, vol. i. p. 314. 



7 " Dell' attrazione di superficie, Mem. II.," Mem. diMatem. et di Fisica 

 delta Soc. Ital. delle Scienze, vol. xii. parte 2 a . Many of Carradori's results 

 and some account of his contest with Prevost are given in the first of the 

 two papers referred to in note l . 



8 Experimental Essays, published in Weale's Series, 1863. Essay I. On 

 the Motions of Camphor on "Water. 



