TRANSACTIONS OF SECTION G. 779 



rapidly die away if once started. If however b be negative, even though very 

 small, the oscillations continually increase in amplitude, and the motion is un- 

 stable. In the case of a synchronous motor, having its field-magnets, armature 

 conductors, and armature so perfectly laminated that no appreciable Foucault 

 currents flow therein, and in which the field current is kept constant, b is negative, 

 and the motion is unstable. In most actual cases, however, this element in b is 

 very small, and is in practice overpowered by true viscous terms, such as arise 

 from Foucault currents in the armature conductors and in tlie substance of the pole- 

 pieces. AVhere motors or converters are used on long transmission lines, however, 

 it may become important, and the motion may be unstable from this cause, giving 

 rise to serious hunting, even with turbine-driven generators. 



The eflfect of damping coils or amortisseurs on the free oscillations is considered 

 and explained. In the case of coils surrounding the pole-pieces, the induced 

 currents set up by the varying armature reaction add a term to b whose sign 

 depends on the load. At light loads it may be negative, and in that case these 

 coils may act as additional causes of unstability. This effect, also, is of com- 

 paratively small importance in ordinary cases, but may become important in 

 motors on long transmission lines. 



The other kind of damping coils, consisting of copper grids let into the face of 

 the pole-pieces, always give rise to true viscous forces, and consequently tend to 

 make the motion stable. Moreover, their effect is much more powerful than is 

 that of coils surrounding the pole-pieces, and by their use it is generally possible 

 to make b positive. 



The effect of damping coils on the forced oscillations can be inferred from the 

 observed rate of damping of the free oscillations, and is generally insignificant. 



7. On Electrical Propulsion as the General Means of Transioort. 

 By James N. Shoolbred, B.A., M.Iiut.C.E. 



The tendency of the last few years has been, in England and elsewhere, to 

 introduce electric-tractive power — on tramways, on railways, on road-carriages, 

 on canals, in automobiles, and in other ways. But these various groups have each 

 been acting independently of the others — isolated, and in some cases actuated, 

 thereto, by motives of jealousy, or of hostility, due to the dread of conflicting 

 commercial interests. 



Besides the above proposed applications for electrical traction, there have 

 sprung up in various directions what may be termed ' universal providers of 

 electricity,' under the head of electrical power schemes, &c. ; to acquire a right, 

 nay, even a practical monopoly, over very large areas, to provide a supply of 

 electricity for, within certain limits, all purposes, whether for locomotion, or for 

 stationary purposes. 



It is only reasonable to suppose that, if instead of a number of conflicting 

 interests, the various parties could be made to combine and fuse together the several 

 portions of their common work, so as to avoid a repetition, and antagonistic, in 

 some cases, of some portions thereof, there might then arise mutual benefit, as well 

 as economy, not merely to the operators themselves, but also to the community at 

 large. One difiiculty lies in the conflicting interests and in the jealousy amongst 

 the various classes of operators. But another danger to the public, more especially, 

 lies in the monopoly which virtually might thereby be aflbrded to the operators. 



An attempt has been recently made by the Liverpool Corporation, the Mersey 

 Docks and Harbour Board, and the South Lancashire Electric Tramways to give 

 expression to this tendency for co-operation among the various workers ; and 

 there are indications in Yorkshire and elsewhere of similar tendencies coming 

 into operation. 



Although the result, so far, of the attempt above referred to has been rather 

 to accentuate than otherwise the difficulties which beset a united imdertaking of 

 suQh a character, yet the benefits which would ultimately accrue to the public 



