178 ANNUAL RECORD OF SCIENCE AND INDUbTRY. 



by Duliamel and philosopliers generally. Gripon finds the 

 explanation of the phenomenon in the resistance of the air, 

 and his observations were made on cords vibratino^ in water, 

 alcohol, oils, and other fluids. He makes the nodal part of the 

 vibrating cord very prettily visible by connecting the cord 

 with the negative end of a galvanic battery, the positive end 

 being a platinum point, movable in the water in a direction 

 parallel to the diflerent parts of the vibrating cord. The 

 cord is thus covered with attached bubbles of hydrogen gas, 

 and these are detached from it only at the points where the 

 vibrations are decided, while the nodal points are marked by 

 the remaining attached bubbles of gas. The distances be- 

 tween the nodal points indicate the pitch of the vibrating 

 cords. Gripon finds that the ratio of the distances for the 

 same cord or spring, when vibrating in the air or in a fluid, 

 varies with the motion of the cord, its density, the density 

 of the liquid, and its viscosity ; and it is the same for oil, 

 which is lighter than water, and for gum-water, which is 

 denser. It is greater for oil than for a mixture of oil and 

 alcohol, liaving the same density. It is greater for Avater 

 and sulphuric acid than in sulphide of carbon, of the same 

 density. A very curious and striking experiment is pointed 

 out by Gripon as a result of this investigation, and one that 

 will probably be hereafter often repeated in the physical 

 lecture-room. It is known that if we put some olive-oil in a 

 proper mixture of alcohol and water, the oil takes a spherical 

 form, and floats in equilibrium in the interior of the mass. 

 Now pass through the centre of such a sphere a fine thread 

 of copper, fixed to the diapason, and when the latter is made 

 to vibrate we shall see the globe of oil revolve about its 

 axis, and flatten by reason of its rotation, provided that the 

 globule is not at a nodal point. Thus the cord is seen to have 

 such a movement that each of its points describes a small 

 elliptical or circular curve. The flattening of the sphere re- 

 alizes the well-known experiment of Plateau. The experi- 

 ment is more difficult with spheres of sulphide of carbon float- 

 ing in a mixture of water and sulphuric acid, because the sul- 

 phide does not adhere to the copper thread, and thus escapes 

 the vibration. Mem. Soc. Lille, 1872, 241. 



