PHYSICAL EXPERIMENTS. 57 



PLATEAU'S EXPERIMENT. 



With the vertical attachment and a tank, made five or 

 six inches deep and with a plane glass bottom, this 

 beautiful experiment, which so well illustrates cohesion 

 and centrifugal force, may be projected. Fig. 36 shows 



the proper conditions. 

 A wire, zc/, is made to 

 revolve vertically i n 

 the tank, by means of 

 a little pulley driven 

 by a cord about a larg- 

 er one, at /, the whole 

 so made as to rest upon 

 the edge of the tank, 

 36. an d supported by ears, 



as shown. The wire, w, should have a thin disk of tin 

 fastened to it at s, for a surface of adhesion. Now the 

 solution may be one of alcohol and water, so graduated 

 that its specific gravity shall just equal that of the oil 

 used, which can only be done by trial in a test-tube ; 

 or it may be a solution of zinc sulphate, and the sphere 

 may be made of bisulphide of carbon, with a little iodine 

 dissolved in it, which will make it black, as in the for- 

 mer experiment described under the head "Cohesion." 

 Here, also, the solution of zinc sulphate and water will 

 need to be of the same density as the bisulphide of 

 carbon, which will be best found by trial. This fixture 

 must be placed upon the apparatus for vertical projec- 

 tion, and the focus adjusted for the sphere. If the 

 above fixture for producing the rotation be made of 

 stiff wire, it will not interfere much with the distinct- 

 ness of the projection. A full account of this experi- 

 ment, and of all the conditions to be observed, will be 

 found in the Smithsonian Report for 1865, p. 207. 



