193 Prof. Thomson on the Mechanical Values of 



height, which was fixed to the centre of the plane circular base 

 of a large copper vessel whose height was 0"12 metre and dia- 

 meter 0'68 meti'e. In both cases the tones produced were 

 exactly the same as those corresponding to the same heights 

 of charge when simple tubes alone were used. 



The same experiments were afterwards made with efflux tubes 

 of larger diameter, the apparatus in other respects being unal- 

 tered ; the agreement in tone between tubes of the same dia- 

 meter throughout and tubes fixed to a much larger vessel, was 

 found no longer to exist. This agreement is likewise destroyed 

 when the height of the glass tube, in relation to that of the vessel 

 placed above, is less considerable ; which shows that the number 

 of vibrations does not depend solely upon what takes place at 

 the orifice itself, but that it depends partially, at least, on the 

 motion of the liquid in the tube. This motion must be modified 

 considerably during the passage of a liquid from a vessel of a 

 large to one of a small capacity ; for at the place of transition a 

 contraction takes place which mast nccessai'ily have 'some influ- 

 ence on the velocity of the liquid in the smaller tube, so that the 

 eff'eet will be the same as a diminution of the charge. 



Savart confirmed the above explanation by fixing a glass tube, 

 with an efilux tube 4'65 millims. in diameter, to the copper vessel 

 above described. The total charge was 1"06 metre. When the 

 upper orifice of the glass tube ^\as partially closed by placing a 

 disc at the bottom of the copper vessel, a depression of tone took 

 place ; at first this depression was inconsiderable, but it was much 

 increased when the disc covered half the orifice. This depression 

 was evidently caused by a diminution of the velocity with which 

 the liquid issued from the efflux tube. 



XXVIII. On the MechanicalValues of Distributions ofElectricitij, 

 Magnetism and Galvanism. By Professor W. Thomson*. 



I. Electridy at rest. 



TO electrify an insulated conductor (a Leyden phial, for in- 

 stance, or any mass of metal resting on supports of glass) 

 in the ordinary way by means of an electrical machine, requires 

 the expenditure of work in turning the machine. But inasmuch 

 as part, ob\'iously by far the greater part, of the work done in 

 this operation goes to generate heat by means of friction, and of 

 the small I'csidue some, it may be a considerable proportion, is 

 wasted in generating heat (electrical light being included in the 



* Communicated by the Author; having been read at a meeting of the 

 Glasgow Philosophical Society, Jan. 26, 1853. 



