September 26, 1884.] 



SCIENCE. 



315 



by actual experiment that the central part of an iron 

 core was not nearly so powerfully magnetized as the 

 outer part. Professor Rowland called attention to 

 the fact that Professor Thompson's experiments had 

 been made with short straight iron magnets, where 

 the resistance of the air to the magnetic lines of force 

 came in as the most important factor, and therefore 

 had led Professor Thompson into error; but that 

 since in the dynamo the only air-spaces are those 

 between the armature and the pole pieces, it closely 

 resembles a ring magnet, where the magnetic circuit 

 is completed in the iron itself, and therefore, as in the 

 ring magnet, the iron in the centre of the core of 

 the magnets of the dynamo is quite as important as 

 that on the outside. 



Professor Fitzgerald of Dublin showed that the 

 loss due to self-induction in the armature is propor- 

 tional to the linear velocity and length of the coils. 



Professor Silvanus P. Thompson of Bristol called 

 attention to the fact, that, whenever a coil is short-cir- 

 cuited, there is a real loss of energy in heat ; and there- 

 fore it is bad to set two brushes, one a little ahead 

 of the other, to reduce sparking, for this prolongs 

 the time during which the single coils are short-cir- 

 cuited. He also noticed that since self-induction is 

 increased in proportion to the increase in the velocity 

 of the armature, or to the increase in the number of 

 turns of wire which it contains, higher electro-motive 

 force is to be best obtained by strengthening the mag- 

 netic field. The speaker then referred to the great 

 importance of using the best soft iron in the field- 

 magnets, instead of cast iron; stating that an English 

 maker had nearly doubled the capacity of a machine 

 by substituting for its old cast-iron magnets and pole- 

 pieces new ones made of best forged iron. Professor 

 Thompson even went so far as to say, that, in his 

 opinion, it was important that the yrain of the iron 

 should run in the same direction as the lines of mag- 

 netic force. The speaker also objected to the use of 

 large masses of iron in the magnets, on the ground 

 that the great time required for such masses to come 

 to their full degree of magnetization interfered with 

 their government. Professor Elihu Thomson, on 

 the other hand, stated that when the iron masses 

 were small, the extra current from the machine had 

 so high an electro-motive force as to make trouble, 

 and, when the machine was used for arc-lights, even 

 caused a sort of vibration in their intensity. 



Prof. F. E. Nipher of Washington University, St. 

 Louis, opened the discussion of the electrical trans- 

 mission of energy by a discussion of the case of two 

 dynamos, one being used as a generator, and one as 

 a motor. He showed that the performance of such a 

 system could be advantageously studied by a series 

 of three surfaces; in each surface two of the variables 

 being the speeds of the two machines, and the third 

 variable being in the three surfaces respectively, the 

 work supplied to the generator, the work done by 

 the motor, and the efficiency of the system as indi- 

 cated by the ratio of these two quantities of work. 



The question of storage-batteries was discussed at 

 considerable length. Mr. W. H. Preece of London 

 opened by a paper upon the subject, giving his expe- 



rience in the use of cells of the Plante form. He 

 has these cells in his house; using electricity not only 

 for lighting, but in many other ways. The cells are 

 charged for two hours every day by a dynamo ma- 

 chine; but he hopes, when the cells are in a little 

 better condition than now, to have to charge them 

 only once a week. Each cell is made up of twelve 

 sheets of lead about a foot square, and separated by 

 thin sheets of hard rubber punched full of holes; 

 the alternate plates are joined together, thus forming 

 two sets of six plates each. Professor Dewar of 

 Cambridge, England, gave an account of the chemis- 

 try of the storage-cell, which was of very great inter- 

 est. There was considerable general discussion upon 

 the subject of the storage-battery, and there still 

 seems to be much to be cleared up in regard to its 

 action. The chemical actions are by no means 

 simple. 



The subject of long-distance telephony and the 

 difficulties that attend it was introduced by Mr. T. D. 

 Lockwood, who in a long and interesting paper gave 

 the results of a great deal of experience with long 

 telephone lines. Some interesting points were brought 

 out. The noises on telephone-lines arise not only 

 from electro-static and electro-dynamic induction, 

 but also from earth-currents and atmospheric elec- 

 tricity, imperfect contacts, and leakage from other 

 lines. Long lines are, of course, more subject to 

 these troubles than short ones; and lines running 

 north and south are more subject to disturbance than 

 those running east and west. Sometimes one end of 

 a line will be noisy and the other quiet, as between 

 Chicago and Milwaukee, where the Chicago end is 

 very quiet, but the Milwaukee terminal is very noisy. 

 Lines subject to pretty uniform leakage are less noisy 

 than well-insulated ones; perhaps, for this reason, 

 lines near the sea are quieter than those inland. 

 Lines on high or mountainous land are subject to 

 periodic storms, the noises being most intense at cer- 

 tain hours of the day. Lines constructed of wire of 

 high conductivity are less noisy than those of greater 

 resistance. Lines of small wire, thus having less 

 electro-static capacity, are less noisy than lines of 

 large wire. A good method of treating a noisy line 

 is to provide a metallic return-circuit, hung parallel 

 to the first, and similarly to it. Many of the sources 

 of disturbance will thus be gotten rid of. In case of 

 a long air-line, ending in a short underground cable, 

 the person at the end of the cable can make himself 

 heard at the other end of the line, but the man at 

 the end of the long line can not make himself heard. 

 For short lines, less than two miles in length, cables 

 of insulated wire covered with tinfoil, this covering 

 being grounded, are useful, and get rid of some 

 sources of disturbance ; but, on account of the large 

 capacity of such a line, the retardation is very great. 



Professor Fitzgerald, who was expecting to give an 

 abstract of the paper read by Lord Rayleigh before 

 the British association, on the subject of long-dis- 

 tance telephony, had been obliged to leave, so no 

 complete presentation of Lord Rayleigh' s results 

 could be obtained: but Professor Rowland made a 

 brief statement of the nature of the problem, that 



