March 15, 1889.] 



SCIENCE. 



195 



months. The advantages of the Faure type are the ease of man- 

 ufacture, and the capacity, which is greater than that of the Plante 

 type. The disadvantages are in the rapid depreciation and the 

 Hmited discharge-rate. 



In the Macrseon battery the attempt is made to take advantage 

 of the good points, avoiding the troubles. This is done in the fol- 

 lowing way. The negative plate is made according to the Faure 

 process, as distinguished from the Plante. A framework of lead 

 is filled in with active material obtained by fusion. The cross- 

 bars making up the frame are thinner than the finished plate, so 

 nothing but the active material is exposed to the liquid. The neg- 

 ative plates are permanently connected to the metallic box, which 

 takes the place of the glass or rubber bo.xes now generally used. 



The positive plates are made according to the Plante plan : the 

 active material is obtained from the support itself by the chemical 

 action of the current. But instead of the forming process taking 

 months to accomplish, as in the original Plante process, it is ac- 

 complished in a few hours, the result of the special electrolyte used 

 in the Macrason battery. The form of the positive plate is also an 

 important question. In this cell it is made of corrugated strips of 



Portable Type for Railroad Purposes. 



lead, fastened at the top to the crossbar of a lead frame, while at 

 the bottom they have a freedom of movement which prevents 

 "buckling" when the strips expand on discharge. These positive 

 plates are fixed to the metallic top of the box. When the cover is 

 in place, the top of the cell is positive, and the bottom is negative, 

 with an insulation between them. The closing of the cell avoids 

 the occurrence of acid fumes, and the evaporation of the acid. 



The following tables give some data as to the performance of 

 the cells : — 



Stationary or " Central Station " Type. 



ELECTRICAL NEWS. 

 The Velocity of Light. 



According to the electro-magnetic theory of light, which recent 

 investigations, mathematical and physical, have rendered so prob- 

 able, the velocity of light is equal to the quantity v, the ratio of the 

 electro-static and electro-magnetic units of electro-motive force. 

 Sir William Thomson has been engaged for some time on a series 

 of measuring-instruments which will, by electro-static force, 

 measure potentials from 40 to 50,000 volts. The method of cali- 

 bration allows a determination of v to be made. The easiest way 

 to get known potentials up to 200 or 300 volts is by sending a 

 measured current through a known resistance, the difference of 

 potential at the terminals of the latter being CR, the product of 

 two easily measured quantities. This is the plan Sir William' 

 adopts for the calibration of instruments giving the lower readings, 

 and the accuracy is within at least one-twentieth per cent. By 

 the aid of condensers, these potentials are multiplied up to 2,000 01 

 3,000 with an accuracy of one-fifth per cent ; and, by the aid of an' 

 intermediary electrometer, this is raised to 10,000 volts, with about 

 the same limit of accuracy. This last measure, based on the- 

 original electro-magnetic determination with the resistance and 

 current may now be compared with the electro-static measurement 

 of the same potential made by an electro-static balance. Sir Wil- 

 liam has not been able to make sure of the accuracy of this last in- 

 strument to within more than one-half per cent, but within this 

 limit the comparison of the two methods gives a ratio withm one- 

 half per cent of 300,000 kilometres per second. The velocity of 

 light is known to be within one-fourth per cent of this value, — a 

 most satisfactory agreement, speaking well for the accuracy of the 

 new instruments. 



The series of ammeters that Sir William lately developed will be 

 of great practical benefit to electricians ; their great range, accuracy, 

 and permanence making them almost invaluable for certain classes 

 of work. The series of volt-meters on which he is working will be 

 of equal value, and we look forward to the time when they will 

 have passed through the experimental stage. 



Absolute Resistance of Mercury. — In a recent number of 

 Wiedemann's Anna!e7i, F. Kohlrausch publishes a redetermination, 

 which he has carried out with elaborate precautions, of the absolute 

 resistance of mercury. The method employed was Weber's method 

 of the damping of a magnet in a coil, with some slight modification 

 of Dorn. The result arrived at is, that the resistance of a cubic 

 centimetre of mercury at o^'C. is 94,060 centimetre seconds. In 

 order to compare this with the B.A. unit, Mr. Glazebrook has com- 

 pared one of the author's mercury standards with the B.A. unit 

 in the Cavendish Laboratory, and finds, that, according to Kohl- 

 rausch's determination, one B.A. is equal to 0.9S66 of an ohm. 

 This would give a length of between 106.2 and 106.3 fo"" the 

 column of mercury of one square centimetre in section, having a 

 resistance of one ohm. 



Electric Locomotives for Mines. — In this country the 

 only applications of electricity to traction in mining, with which we 

 are acquainted, is in Lykens, Penn. In this, current is conveyed tcs- 



