VI. MISCELLANEOUS. 149 



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

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

 spreading from the centre between the two plates, bears upon these a pressure 

 measured by its elastic force and by the extent of the surfaces brought into 

 apparent contact. When this pressure equals or exceeds the weight of the 

 plates acted upon, this is upheld in the air, where it becomes subject to extra- 

 ordinary mobility. Having no longer any weight, the friction which is pro- 

 portioned to weight is annulled, and the resistance no longer depends on that 

 property scarcely yet studied, the viscidity of the air. 



682. Rotation Apparatus for determining the effect 



of Atmospheric Resistance on bodies of different shapes, 

 particularly on projectiles. Constructed by Theodor Baumann, 

 junior, Mechanical Engineer, Berlin. 



Professor Dr. E. E. Kummer, Berlin. 



(See " Abhandl. der Konigl. Akademieder Wissenschaften in Berlin, 

 1875 "; " Uber die Wirkung des Luftwiderstandes." by E. E. Kummer. 



683. Two Apparatuses 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.) 



684. Apparatus to illustrate to a large audience the fact 

 that the pressure exerted by a curved liquid film increases 

 with the curvature. 



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 at 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's 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. 



686. Apparatus for determining the Tension of the Vapours 



of different liquids at the boiling point. Prof. W. F. Barrett, 



