1895.] Alternate Current Dynamo-Electric Machines. 89 



if the atomic weight of argon be 40, on subtracting 32, or twice the 

 average difference, the number 8 is obtained, which closely approxi- 

 mates to 3'9 x 2. Which of these views is correct time must decide. 



II. "Alternate Current Dynamo-Electric Machines." By J. 

 HOPKINSON, F.R.S,, and E. WILSON.* Received April 4 ? 

 1895. 



(Abstract.) 



The paper deals experimentally with the currents induced in the 

 coils and in the cores of the magnets of alternate current machines 

 by the varying currents in and the varying positions of the armature. 

 it is shown that such currents exist, and that they have the effect of 

 diminishing to a certain extent the electromotive force of the machine 

 when working on resistances as a generator without a corresponding 

 effect upon the phase of the armature current. It is also shown that 

 preventing variations in the coils of the electromagnet does not, in 

 the machine experimented upon, greatly affect the result, and that 

 the effect of introducing copper plates between the magnets and the 

 armature has not a very great effect upon the electromotive force of 

 the armature, the conclusion being that the conductivity of the iron 

 cores is sufficient to produce the main part of the effect. A method 

 of determining the efficiency of alternate current machines is illus- 

 trated, and the results of the experiments for this determination are 

 utilised to show that in certain cases of relation of phase of current to 

 phase of electromotive force, the effect of the local currents in the 

 iron cores is to increase, instead of to diminish, the electromotive force 

 of the machine. 



III. "Note on the Relations of Sensory Impressions and 

 Sensory Centres to Voluntary Movements." By H. CHARL- 

 TON BASTIAN, M.D., F.R.S. , Professor of Clinical Medicine 

 in University College, London. Received April 5, 1895. 



In a recent communication to the Royal Society by Drs. Mott and 

 Sherrington, entitled "Experiments upon the Influence of Sensory 

 Nerves upon Movement and Nutrition of the Limbs," results of a 

 most important and hitherto unsuspected character were brought 

 forward. In this communication they have shown that " section of 

 the whole series of sensory roots belonging to a limb," either upper 



* The large majority of the experiments herein described were made in the 

 summer of 1893, and a considerable part of the paper was then written. We have 

 to thank Mr. F. Lydall, one of the student demonstrators at King's College at that 

 time, for much assistance. 



