Oscillatory Discharges. 2 



secured to the spindle A', where in the ordinary manner 

 the mirror S' is fixed. The spindles are kept in position 

 by the screws W, V'V'. These screws are pierced through 

 their whole length, and they carry sapphire pillows, also 

 pierced in order to allow of an abundant oiling, which has 

 to be made all the time the turbine is working. 



At the beginning we availed ourselves of a much over- 

 heated jet of aqueous vapour to start the apparatus, but later 

 on we found it more convenient and suitable to make use of 

 a jet of air compressed to 6 atm., taken from a large 

 reservoir. 



The regularity of speed of the turbine depends very much 

 on the oiling of the spindles, which should be continuous but 

 not excessive. The rotation of the axis becomes in fact very 

 irregular by lack of oil, the friction being then too great, as 

 well as by an excess of it, as in this case some oil will enter 

 between the moving disk and the distribution box. 



It is, moreover, absolutely necessary that the air injected 

 into the turbine should not carry any oil -drops on to the 

 pump, nor dust particles of any considerable size, as the 

 turning and the fixed parts are distant from one another only 

 t 2 q of a millimetre. To ensure this the air was admitted 

 through a large recipient fitted with a long filter formed by 

 several sheets of straight metallic nets. 



To ascertain the velocity of rotation a small and light 

 aluminium disk, to whose edge a short hair was attached, 

 was fixed on the axis A of the turbine. Next to this disk a 

 rotating brass cylinder covered with smoked paper was 

 disposed, the hair making a mark on the paper at each turn of 

 the axis of the turbine. 



The time interval corresponding to the interval between 

 two marks made by the hair, and hence the number of turns 

 effected per second by the rotating axis, was deduced in the 

 usual manner from a comparison with the oscillation curve 

 of an electromagnetic tuning-fork (whose period of oscillation 

 was accurately known), recorded on the same cylinder. 



A conveniently regulated clockwork was fitted with a 

 contrivance enabling the cylinder to effect one turn only, 

 with suitable velocity, so that the cylinder, after a small 

 fraction of a turn (say about £), reached a fairly constant 

 speed. 



Fig. 2 (p. 10) represents a general view of the turbine, the 

 rotating cylinder, and the tuning-fork. 



Two solid iron rods, fastened on the turbine columns, 

 carried a small frame with the photographic plate, whose 

 dimensions were 3x 12 cm. 



