802 REPORT — 1895. 



Immediately below it, within the box, is a white screen capable of adjustment at 

 different angles and two small electric lamps of different candle-power, either or 

 both of whicli can be used. A portable secondary battery is used to supply them 

 with current. The illumination of the hinged screen inside the box varies 

 approximately as the cosine of the angle of incidence of the light from the electric 

 lamps upon 'it. A handle with a pointer moving over a graduated scale is 

 connected to the screen with a system of levers, and the inclination is so adjusted 

 that the illumination of the screen is equal to that of the perforated diaphragm, 

 the perforations seeming to disappear when this balance is affected. The illumi- 

 nation can then be read off on the scale in units of the illumination due to one 

 standard candle at one foot distance. The object of the levers 13 to give an open 

 and convenient scale. The scale is graduated by experiment, and does not depend 

 upon the cosine law. The colour difHculty, where arc light or daylight is to be 

 measured, is reduced by the use of a yellow-tinted diaphragm and a blue-tinted 

 screen, the tints being "selected so that the readings are the same as the mean of a 

 large number of measurements made with white screens. By means of a 

 graduated quadrant and a gnomon the angle and the cosine of the angle of 

 incidence of the light from a lamp may be measured, and rules are given for 

 deducing the height of the lamp and the slant height, and hence the candle-power 

 of the lamp. 



3. On Storage Batteries. By H. A. Earle. 



The author traced the history of storage batteries from the time when Gautherot, 

 in 1801, obtained secondary currents from silver and platinum plates which had 

 been used in a voltameter to decompose a saline solution. Hitter, in 1808, was the 

 first to make a secondary battery, in which he employed plates of gold separated 

 by cloth or paper, moistened with a saline solution; and though he employed 

 various metals, including lead, the secondary currents he obtauied were only of 

 short duration, and the batteries of only scientific interest. It would naturally be 

 presumed that he would have noticed' increased effects when using lead, but we 

 find that lie used salt water and not an acid solution, and on this account chloride 

 of lead was formed, which is scarcely soluble and is a bad conductor. 



De la Rive in 18:30 obtained secondary currents from platinum plates in a 

 voltameter filled with water, and he closely 'approached the elements of our present 

 storage cells when, among his many experiments, he used in a primary battery a 

 platinum plate covered with a film of peroxide of lead, and a zinc plate immersed 

 in an acid solution. 



The first powerful storage battery was introduced by Plante in 1800, but the 

 method employed for its formation was too long and costly for practical purposes. 

 Faure, in 1881, reduced this long process of formation by applying lead oxide in 

 the form of a paste to the surfaces of the plates, but the adhesion was msufScient, 

 and the life of the cells was too short to give them commercial value. Swan 

 realised that the active material required a better mechanical support, and introduced 

 a plate of grid form, the interstices serving to retain the material ; and thisirame, 

 combined with the Faure pasting, was the origin of the plates largely used in this 

 country and elsewhere. 



The monopoly that existed for the manufacture of this plate caused other 

 makers to turn their thoughts to the plain lead plates, and such great advances 

 have been made both in their manufacture and method of formation, that it is 

 rapidly replacing the pasted form. 



A type that differs greatlv from the solid lead plate, but which is not pasted, 

 is the chloride plate, in which the material to become active is a mixture of 

 chloride of lead and chloride of zinc cast into small tablets, which are fraff ^d by 

 casting antimonious lead around them under high pressure. The sulbequent 

 elimination of the chloride and zinc leaves a porous structure of pure lead of a 

 crystalline nature, of good conductivity, and with a large surface exposed to the 

 electrolyte, the result being a large capacity for a given weight, and for the space 

 occupied. 



