On Friction and Heat- conduction in rarefied Gases. 53 



Soon after my return I tried an experiment at some Iron-works 

 to make such a cone. A large sheet of iron with a hole in the 

 centre was placed over a pipe proceeding from the blast. A 

 quantity of cinders and ashes were supplied to the pipe, and in a 

 short time a cone was built up. For the purpose of lecture-illus- 

 tration the apparatus about to be described is convenient, and 

 shows very clearly the formation of volcanic cones. It consists 

 of a wooden trough about 18 inches long, with sloping sides ; at 

 the bottom of the trough there is a bladed screw to carry forward 

 the ashes, sawdust, or other material used, to an opening through 

 which air from a powerful bellows is forced upward in a vertical 

 stream. A board 3 or 4 feet square with a hole in the centre is 

 placed over the air-jet, so that on turning the screw the sawdust 

 is carried into the stream of air ; it is then thrown vertically up- 

 ward through the hole in the upper board, and on falling down 

 builds up a cone having many of the peculiarities of a natural 

 one. Thus, the angle of slope is almost identical ; the sorting 

 of materials is similar, the heaviest portions being near the 

 crater, while the finer particles and dust are carried to a great 

 distance. If, while the miniature eruption is going on, the oxy- 

 hydrogen light be directed horizontally on to the cone, it will be 

 seen that the dust is carried to a distance of many feet. Using 

 alternately sawdust of different colours, the structure of the cone 

 is well seen on making a section of it. This is easily done by 

 cutting vertically through the cone with a sheet of cardboard 

 and sweeping off one half of the mound into a tray. If the jet 

 of air be vertical and the air of the room is still, the lip of the 

 crater is horizontal ; but if the apparatus be near the door or 

 where there is a draught, the materials are carried to one side, 

 and the cone is built up much higher on one side than the other. 

 The same thing, of course, will occur if the jet is not vertical ; 

 and as from accidental circumstances the jet frequently changes 

 its direction, a considerable variety of cones is sure to be obtained 

 in a series of experiments. 

 Birmingham, May 15, 1875. 



IX. On Friction and Heat -conduction in rarefied Gases. 

 By A. Kundt and E. Warburg*. 



OUR knowledge of the properties of gaseous bodies has of 

 late years been considerably extended by the consequences 

 deduced from the kinetic molecular theory of these bodies estab- 

 lished by Clausius. The remarkable laws theoretically disco- 



* Translated from the Monatsbericht der Koniglich Preussischen Aka- 

 demie der Wissenschaften, February 1875, pp. 160-173. 



