190 Prof. G. Luvini's Experiments and Observations 



tance cannot be supposed entirely independent of the position of 

 the sun. 



The truth will lie within the results of the calculation on these 

 three assumptions. We see, then, that a large percentage of 

 those comets which approach the sun in hyperbolic orbits will 

 have orbits with excentricities greater than 1'02. Now out of 

 the large number of comets whose orbits have been carefully cal- 

 culated not one has an excentricity greater than 1*02 ; and we 

 are therefore led to the conclusion that though several known 

 comets are probably moving in hyperbolic orbits, yet by far 

 the greater number of those comets whose orbits are undistin- 

 guishable from parabolas are moving in elliptic orbits of very 

 great length. 



Roundhay Vicarage, 

 August 2, 1870, 



[To be continued.] 



XXIII. Experiments and Observations on the Adhesion between 

 Solids and Liquids. By Giovanni LuviNi, Professor of 

 Physics in the Royal Military Academy of Turin*. 



M PLATEAU, in the Eighth Series of his Theoretical and 

 • Experimental Researches on Liquidst, describes the 

 results of a very beautiful experiment from which he deduces 

 some important consequences. In a cylindrical glass vessel, 11. 

 centims. in diameter, he arranged a magnetic needle in the form 

 of a rhomb 10 centims. in length, 7 millims. in width, and 0*3 

 millim. in thickness, turning in a horizontal plane on an axis 

 coincident with that of the vessel. The needle being moved 90° 

 out of its position of equilibrium and left to itself, returned back 

 with a velocity depending on its length, on the magnetic inten- 

 sity of the earth and of the needle, and on the passive resistance 

 that the needle had to encounter during its return motion. M. 

 Plateau arranges the experiment in such a manner as to be able 

 to measure with great precision the time occupied by the needle, 

 after it has been turned out of its plane, in traversing the first 

 85° towards its position of equilibrium. A liquid is poured into 

 the vessel to such a height as to reach to the under surface of 

 the needle, so that this may rest upon the liquid while the upper 

 surface is exposed to the air. Under these conditions we have 

 to determine the time occupied by the needle in traversing the 

 first 85° upon the surface of the liquid. In another form of the 



* Translated by Charles Tomlinson, F.R.S., from the Proceedings of the 

 Royal Academy of Sciences of Turin of the lUth of June, 1870. 



t Transactions of the Academy of Sciences of Brussels. Presented to 

 the Academy July 4, 1868. 



