VII. FRICTION. 12" 



549. Attwood's Machine with water clock attached. 



The Council of the Yorkshire College of Science, Leeds. 



The time is measured by a water clock, the orifice of which can be opened by 

 means of a lever moving under the influence of an electro-magnet. The weights 

 are supported by a thread grasped by a pair of iron pincers, which are kept shut 

 by a spring, but can be opened by means of another electro-magnet included in 

 the same circuit as that attached to the water clock, so that the water begins 

 to flow and the weights to fall simultaneously. Another metal piece can be 

 screwed on to the instrument. One of the binding screws with which it is 

 furnished is insulated from it by a plate of ebonite pierced with a shut metallic 

 rod in connexion with the binding screw, and on which rests one extremity 

 of a lever in electric communication with the rest of the piece. This 

 piece being included in the circuit the current cannot pass when the lever is 

 raised, and the water clock is stopped as soon as this is effected by the falling 

 weight. 



549a. Attwood's Machine, with friction rollers and electro- 

 magnetical release. Ferdinand Ernecke, Berlin. 



549b. Attwood's Machine, with pendulum attached. 



Rohrbeck and Luhme, Berlin. 



VII. FRICTION. 



55O. Apparatus for determining the Friction between 

 Water and Air. 



Professor Viktor von Lang, Vienna University. 



The above consists of a heavy stand with one fixed and three movable 

 arms. The fixed arm bears a short glass tube, from which a continuous 

 stream of water is made to flow. A crosspiece of four glass tubes is united, 

 air-tight, by its longest arm to the water-delivering tube ; the opposite arm is 

 directed downwards, and closed by a caoutchouc mouthpiece passing over 

 the " aspirating tube." This latter is supported by the two lowest arms of 

 the stand, the remaining fourth arm securing the crosspiece. The stream of 

 water passing through the " aspirating tube " moves the air, the quantity 

 of which is determined by the motion of a soap lamina in the " measuring 

 tube." This tube is joined to one of the horizontal arms of the crosspiece, 

 the fourth arm bearing a water manometer. 



550a. Machine for the Examination and Measurement 

 of the Sliding Friction caused by the Motion and the Variable 

 Velocity on Bails. Constructed by _Herr Jung, at the Uni- 

 versity of Giessen. 



This machine includes : 



a. A board, with hooks for attaching a scale by means of a 



cord running on a roller, for the purpose of measuring 

 the friction. 



b. Two pairs of iron and brass rails, to be fixed to this board. 



c. Three pairs of wooden rollers. 



