366 



SCIENCE. 



[Vol. XIII. No. 327 



difficulties which had seemed inherent to that type of apparatus. 

 The Tesia motor is now controlled by the Westinghouse Electric 

 Company, and that powerful organization has been exerting all of 

 its energies to make the machine a success, but apparently to no 

 great effect. 



There comes from Europe, however, the account of a new motor, 

 which, if we are to believe the figures given, accomplishes all that 

 the Tesla motor promised ; and while the latter required a special 

 distributing system, using at least three wires to bring current to 

 the motor, the new machine can be used in connection with the 

 ordinary alternating system employed for incandescent lighting, 

 and only two wires are necessary for the connections. 



Messrs. Ganz & Co. of Buda-Pesth have been engaged for four 

 years in experiments on various forms and types of alternating- 

 current motors. Their most recent production gives results such 

 that they feel confident that the performance of continuous-current 

 motors will be attained. The machine in question gave, at 730 

 revolutions, 30.7 horse-power, or 22,700 watts of work, while the 

 apparent energy consumed was 29,800 watts, and the real energy 

 27,700 watts, thus giving an efficiency of 80.9 per cent. The ratio 

 between the real and apparent energy consumed was .92, or nearly 

 unity, and this is a very important point. Ordinarily the ratio is 

 less than one-half, the difference of phase between the current and 

 electro-motive force being considerable ; so that a great deal of 

 current flows through the motor, which does little more than heat 

 it, the machine running first as a motor, then as a dynamo, the 

 difference between the work done on and by it being small, while 

 the current might have a considerable value. The figures given 

 above were obtained from a model, which was not constructed to 

 give the greatest possible efficiency or output, but which was de- 

 signed for purposes of study. When properly made machines are 

 turned out, the efficiency should not be less, according to the de- 

 signers, than 90 per cent. 



It is a pity that no description of the machine, nor more accurate 

 •experimental data, is available. One can hardly see why such very 

 meagre results should be sent out by the makers. If any thing is 

 given, it should be enough to enable people to judge for themselves 

 the merits of the invention ; but the firm of Ganz & Co. is one of 

 great respectability, and there seems to be now some hope that a 

 successful alternating-current motor has been discovered. 



Relation between Density of Acid and Capacity in 

 Secondary Batteries. — M. Heim, at the Electro-technical 

 Institute at Hanover, has experimented on the capacity of storage- 

 ■cells with different strengths of acid. Two types of cells were 

 used, — the Tudor and the Julien. These had a normal capacity 

 -of about 50 ampere hours ; and, for a first experiment, acid of a 

 strength of from 15 to 20 per cent was used, and the cells were 

 charged and discharged three times, there being an interval of a 

 day allowed between the charge and discharge. The next step 

 was to fill the cells with acid of a strength of, say, 9 or 10 per cent, 

 and again determine the capacity, there being always a number of 

 discharges for each strength of acid, the discharge always lasting 

 ■until the electro-motive force had fallen 10 per cent from its origi- 

 nal value. The results obtained are, that the capacity increases 

 •rapidly with an increase of from 10 to 14 per cent in the strength of 

 the acid ; that it reaches a maximum at a strength of 16 per cent; 

 then decreases slowly at first, and afterwards rapidly, as the density 

 of the solution increases. M. Heim also made experiments to find 

 •out the strength of solution at which the support-plate begins to be 

 attacked. He found that strengths even as low as 20 to 25 per 

 ■cent were too concentrated, and, as the result of his work, recom- 

 mends a density of 16 per cent (1.108). This is not so high as that 

 ordinarily employed, the usual density varying from 1.150 to 1.200. 



A New Arc-Lamp. — A new type of arc-lamp has been intro- 

 duced into England from France by the Planet Electrical Engi- 

 neering Company. The upper carbon is fed by means of an elec- 

 tric motor which drives a worm and a train of gearing. The field- 

 ■magnets of the motor are in series with the arc, the armature being 

 connected as a shunt to the field-magnets. The difference of po- 

 tential at the two brushes of the motor is two volts. When the 

 lamp is burning steadily, the motor is at rest ; but, when the re- 

 sistance of the arc increases, a solenoid core pulls down a lever. 



making contact to the armature, which immediately commences to 

 revolve. Should the arc be made too short, the solenoid reverses 

 the connections, and the armature revolves in the opposite direc- 

 tion. The advantage of the arrangement is, that there is plenty of 

 power to overcome the friction of the slide, and that, with the ex- 

 ception of the solenoid, there are no fine adjustments. 



Quartz as an Insulator. — At a recent meeting of the Lon- 

 don Physical Society, Mr. C. V. Boys read a paper on the above 

 subject, which is not without some practical interest. It will be 

 remembered that Mr. Boys some time ago succeeded in obtaining 

 extremely fine and strong fibres of quartz by shooting an arrow to 

 which was attached a piece of quartz softened by heat. These 

 fibres may be used instead of silk for delicate suspensions in elec- 

 trical instruments. In making these fibres, Mr. Boys observed 

 that if they were very fine, and broke between the bow and the 

 target, the extremities assumed the form of a screw about half an 

 inch in diameter and eight or ten inches long. If any body were 

 brought near this screw, the end of it would shoot out toward it, 

 retreating again when the body was removed. It hardly seemed 

 possible to account for this in any other manner than by suppos- 

 ing the fibre to be electrified. If this were the case, it would show 

 that quartz was an exceptionally good insulator, since ordinarily the 

 exceedingly minute charge on the extremely slender fibre would be 

 dissipated almost as soon as it was formed. Carrying his experi- 

 ments further, Mr. Boys found, that while, even under any circum- 

 stances, quartz is a better insulator than glass, under ordinary at- 

 mospheric conditions there is no comparison between them. To 

 show these insulating properties, a gold-leaf electroscope was 

 made, the leaves being suspended by a quartz hook. In order to 

 make the conditions as unfavorable as possible, a dish of water 

 was placed in the case. After five hours, the deflection of the 

 charged leaves had only decreased about a quarter. If glass had 

 been substituted for the quartz, the leaves would have been com- 

 pletely discharged in considerably less than a minute. As quartz 

 can be easily softened, and can be readily worked when soft, it 

 should be of great value for electrostatic instruments, where there 

 is always great trouble from leakage. Mr. Boys stated that even 

 when quartz was dipped in ammonia, or boiled in potash, it only 

 required washing to completely restore its insulating properties, 

 and, even when it is raised to a red heat, these properties are re- 

 covered on cooling. Some quartz which was kept in fused potash 

 for a considerable time lost its insulating properties to some extent ; 

 but, even after this treatment, it was better than glass. 



HEALTH MATTERS. 



Ventilation. — The Sanitary News gives the following advice 

 in reference to the admission of air to rooms : " Air should be in- 

 troduced and removed at those parts of the room where it would 

 not cause a sensible draught. Air flowing against the body at, or 

 even somewhat above, the temperature of the air of the room, will 

 cause an inconvenient draught, from the fact, that, as it removes 

 the moisture of the body, it causes evaporation or a sensation of 

 cold. Air should never, as a rule, be introduced at or close to the 

 floor-level. The opening would be liable to be fouled with sweep- 

 ings and dirt. The air, unless very much above the temperature of 

 the air of the room, would produce a sensation of cold to the feet. 

 It may be regarded as an axiom in ventilating and warming, that 

 the feet should be kept warm and the head cool. The orifices at 

 which air is admitted should be above the level of the heads of the 

 persons occupying the room. The current of inflowing air should 

 be directed toward the ceiling, and should either be as much sub- 

 divided as possible by means of numerous orifices, or be admitted 

 through conical openings with the smaller opening toward the outer 

 air and the larger openings toward the room, by which means the 

 air of the entering current is very rapidly dispersed. Air admitted 

 near the ceiling very soon ceases to exist as a distinct current, and 

 will be found at a very short distance from the inlet to have min- 

 gled with the general mass of the air, and to have attained the tem- 

 perature of the room, partly ovving to the longer mass of air in the 

 room with which the inflowing current mingles, partly to the action 

 of gravity in cases where the inflowing air is colder than the air in 

 the room." 



