790 KEPORT— 1903. 



The excitation was kept constant, so that tlie torque was proportional to the 

 current. Thus the extra current required to maintain a given speed after the disc 

 had been fixed to the shaft gave the torque absorbed by the disc. 



There was found to be an angular speed for each disc above which the torque 

 was accurately proportional to about the 2'5th power of the speed. This critical 

 speed appeared to vary inversely as the square of the diameter. Below it the law 

 followed was of a lower decree ; but owing to the multiplication of errors of 

 measurement no definite conclusion as to its exact nature was arrived at. 



As the three discs originally tried gave uncertain results as to the effects of 

 size, a much lai'ger one, nearly 4 feet in diaraetei', was also tried ; and as a result 

 of all the experiments it was concluded that the torque varies as about the 5'5th 

 power of the diameter. 



To give an idea of the amount of power thus absorbed, it may be stated that 

 a disc of 47 inches required ^^ H.P. to keep up a constant speed of SOO revolutions 

 per minute, and that if the above law holds a 9-foot disc would absorb 10 H.P, 

 at the same speed. 



6. On Monophase Induction Hepulsion Motors. 

 By William Gramp, A.M.I.E.E. 



The repulsion motor has in the single-phase system the functions of the direct 

 series motor in the direct current system of electrical distribution, possessing the 

 advantage of a large starting torque. In construction the repulsion resembles the 

 direct current motor, with the field laminated ; the armature-brushes are short- 

 circuited, and the field only is connected to the supply-mains, which constitutes a 

 great advantage over the alternate-current series motor. Two classes of repulsion 

 motors are examined: (1 ) those with deliuite poles, and (li) those without definite 

 poles ; and each, again, may have either («) open-circuited or {b) closed-circuited 

 rotors. Theoretically the repulsion motor is always a special case of the alternate- 

 current transformer. The action is shown by a model which takes into separate 

 account the phase in time, and the position in space of the current or of the field pro- 

 duced thereby. Class 1 have usually smaller starting torque, a lower maximum 

 speed, and a more sparkless commutation than Class 2. The locus of the extremity 

 of the primary current vector plotted for current and power- factor is approximately 

 a narrow semi-ellipse ; the higher the ratio pole-arc : pole-pitch, the more nearly 

 does the curve approach a semicircle, provided that the brushes be moved a.s the 

 load alters. 



Open-circuit motors have their current formula and calculations complicated 

 by the presence of an exponential term, which also renders commutation more 

 difficult and tends to reduce the torque of the motor and to shift the rotor current 

 in phase a little. 



The author has tried practically three dilTerent motors, each of which was 

 repeatedly varied in its details; he finds that in every case by suitable sub- 

 division of the armature-coils the motor may be rendered sparkless. The starting 

 torque may be made very large indeed, one rotor .starting under full load, with at 

 most only one-and-a-half times full-load current. 



Other practical points are: (1) the advantage of working with high air-gap 

 density ; (2) the need for extreme rigidity of the l^earings to a^oid contact between 

 rotor and stator ; (3) the capability of the machine to run well above synchronism. 



7. On the Ventilation of Tnhe llaihvays. 

 By 3. W. Thomas, F.I.C, F.CS. 



The physical conditions essenti.al to good ventilation in tube railways are 

 chietiy dealt with in the paper, and it is calculated that the forces brought into 

 play by the moving trains and the natural heat of the tubes will be ample if properly 

 directed. In tube railways, if B is the centre of three statiou.s, the down train 

 moving from A to B will draw air from the A station into the tube and expel if 



