176 SEC. 5. MOLECULAR PHYSICS, 



VI. MISCELLANEOUS. 



680. Apparatus, serving to illustrate the Mechanical 

 Effect of the Expansion of Liquids. T. A. Snyders, Delft. 



Consisting of gun-barrels closed by a lead plate 3 millimetres thick, which 

 is retained by a perforated screw-plug. The expansion of the liquid causes 

 a cylinder of lead to be forced out through the aperture of the plug. 



681. Apparatus, constructed by Leschot and Thury, to 

 suppress Friction by the interposition of a stratum of air. 



Geneva Association for the Construction of Scientific In- 

 struments. 



The apparatus is composed of two plates, superposed, and perfectly 

 adjusted, between which is introduced air or gas under pressure. The air, 

 spreading from the centre between the two plates, exerts upon these a total 

 pressure measured by its elastic force multiplied by the extent of the surfaces 

 brought into apparent contact. When this pressure equals or exceeds the 

 weight of the plate acted upon, it supports the plate, and the friction is re- 

 duced to its smallest limits. 



683. Two Apparatus for measuring the Transpira- 

 tion of Air at different Temperatures. 



Dr. 0. E. Meyer, University of Breslau. 

 (Described in "Poggend Ann., 1873," vol. 148, p. 203.) 



634. Apparatus to illustrate to a large audience the fact 

 that the pressure exerted by a curved liquid film increases 

 with the curvature. The Yorkshire College of Science. 



The apparatus consists of a glass tube communicating with two others, 

 each of which is furnished with a stop-cock. Bubbles of different diameters 

 are blown at the ends of the tubes, one stop-cock being closed while the other 

 is open, and then communication with the outer air being cut off, and the 

 cocks both opened, the smaller bubble is seen to diminish and the larger one 

 to increase, thus proving that the air inside the smaller bubble was the more 

 compressed. The tubes are bent, so as to bring their extremities close 

 together, and the experiment can be shown to a large audience by throwing a 

 magnified image of the bubbles on a screen. 



685. Apparatus for demonstrating Leidenfrost's phe- 

 nomenon of drops. Dr. J. Hoogewerff, Rotterdam. 



This apparatus was constructed by Mr. Kellenbach, curator of the Batavian 

 Society, Rotterdam, and belonging to the academy of plastic arts and tech- 

 nical sciences at Rotterdam. The apparatus is used as follows : a Grove 

 pile is connected with the instrument, a galvanometer being placed on the 

 conducting wire, and the copper tray or platinum capsule into which the 

 drops of water have been put, are heated by means of a gas lamp. Every 

 time Leidenfrost'B experiment is repeated, no current is indicated by the gal- 

 vanometer, contact having been interrupted by the layer of steam ; when on 

 the contrary the water, the surface of which is in contact with the copper 

 wire, comes into immediate contact again with the metallic surface of the 

 tray or capsule, the galvanometer distinctly indicates the current. 



