436 beport — 1878. 



upon the amalgams of the positive metals are increased ; hut in hydrogen, carhonic 

 acid, nitrogen, and coal-gas, the motions are instantly arrested. 



The author concludes that the motions result from an alternate play of deoxi- 

 dation of the mercury underneath the acid by electrolysis, due to the currents of 

 small floating particles of the positive metal, causing the drop to contract, and of 

 oxidation of the surface outside the acid-drop, causing it to re-expand. 



9. Note on Surface Tension. By George Francis FitzGerald. 



Assuming that the contact difference of electric potential at the junction of 

 two dissimilar fluids is due to a tendency towards some chemical combination of 

 the two, it is easy to see that if \ De the electrical charge corresponding to each 

 electro-chemical equivalent, which is the same for all hodies, and if n he the 

 numher of such equivalents in presence of one another per unit of surface, and if 

 ( he the difference of potential of contact, then there is a potential energy per 

 unit of surface = wx« and this must he the superficial tension if it be all due to 

 this cause, as M. Lippman's recent experiments seem to show. Hence 



T = «X<- . . . 



If e he assumed about '1 of a volt, and T = '08 grammes per. centimeter, as it is 

 in the case of water, it is possible to calculate the thickness of the superficial layer 

 which contains molecules which act upon one another, and the result is 



= 7 '8 x 10" 8 of a centimeter, 

 which approximates towards the quantities ohtained by other methods. 



10. New Application of Gas for Lighthouses, illustrated by Models, full-sized 

 Apparatus, S,-c* By J. R. Wigham, M.B.I.A. 



I. The Quadriform Group Flashing Light at Galley Head Lighthouse. 

 The following are the chief points insisted on hy the author : — 

 Importance of the position of Galley Head. Desire of the Commissioners of 



Irish Lights to ohtain the best light there. Principle of Wigham's patent gas- 

 hurner explained. Result, the greatest possible intensity of light, comhined with 

 large volume. Method of increasing the power of burner by 5 steps, according to 

 the state of the weather. Effect of lenticular apparatus upon such flames. Effect 

 upon fogs of such flames. Method of still further increasing their power by doubling, 

 trehling, and quadrupling the number of burners and lenses in each lighthouse. 

 Method of arrangement so as to admit of one light being over another, not only 

 without injury to the upper lights, but so as to give each of them increased illumi- 

 nating power. Burners, lighthouse lens, and model of Galley Head Lighthouse to 

 illustrate the above. A first-order quadriform light, hy permission of the Commis- 

 sioners of Irish Lights, exhibited at Howth Bailey Lighthouse, entrance to Dublin 

 Bay, during the meeting of the British Association. Place of observation — Salt- 

 hill, Kingstown. Importance of flashing great lights in suddenly illuminating fog, 

 so as to arrest the eye of the mariner when the light itself is invisible. 



II. The Comhined Gas and Electric Light for Lighthouses. 

 In this paper the author discussed : — 



Limit as to size of lighthouse lights attained by the quadriform light referred 

 to ahove in Part I. Further intensity desirable. Core light introduced into focus 

 of lenticular apparatus. Various kinds, of cores — magnesium, lime light, &c. Im- 

 provement in the Gramme machine rendered electric light suitable as a core. 

 Jahlachkoff candle available. Effect of the electric core. Cost of same. Power of 

 sudden flashes of electric light upon fog in arresting the attention of the mariner. 

 There was an exhibition of this core light at Howth Bailey, hy permission of the 



* These papers were published in extenso in 'Engineering,' August 23, 1878. 



