THE SMITHSONIAN INSTITUTION. 353 



strong enougli by which to read fine print at the distance of {i a metre. 

 Comparing this exceedingly small effect with the brilliant illumina- 

 tion produced by oG sine and carbon, or sine and plntinwni elements, 

 it is difficult to comprehend how Mr. Weekes can cherish the hope 

 that such batteries may become advantageous means of illumination. 

 The plates of Mr. Weekes, it is true, were placed in rather dry 

 ground; if placed in moister ground they would have yielded a 

 stronger current ; but it could never be as strong as if the plates 

 were immersed directly in water. By moistening the sand with a so- 

 lution of sal-ammoniac the strength of the current will still nex^er ap- 

 proach that which tlie same plates would produce if placed in the 

 vsolution v»athout tlie sand. Buried plates can be used profitably 

 only when very weak currents are desired ; but such currents can l^ 

 obtained quite constant for a long time by using very dilate acid. 

 Buried plates, however, have the disadvanttige of being less accessi- 

 ble than those of other batteries. 



§ 16, Smee's battery. — This battery was greatly praised in many 

 quarters ; it was represented to produce very strong currents, and to 

 be far more constant than other batteries with one liquid. No meas- 

 urements in support of this opinion were made, and I have not 

 found it anywhere confirmed. 



The copper of Wollastoa's battery is substituted in Sraee's by pla- 

 tinum or silver, covered by a rough surface of platinum (platinraoor.) 

 This coating of platinum is produced by immersing the perfectly clean 

 plate in a solution of chloride of platinum and potassium in contact 

 with the negative pole of a rather weak battery, the positive pole of 

 wliich dips at the same time into the solution. The platinum de- 

 [X)sites on the plate at the negative ])o]e. If the positive pole be also 

 a plate of platinum, it will be attacked by the chlorine, and the solu- 

 tion will be kept saturated. 



The two surfaces of Sraee's platiniz;ed plate are placed at about one 

 line distance from the zinc plates. The width of the zinc plates is to 

 be only about three-quarters that of the platinized plate. What is 

 to be expected to be gained by this I cannot see. It is not the case in 

 the Smee element with which 1 experimented, the negative plate of 

 which was platinized silver. 



I found this battery less constant than Wollaston's, and the varia- 

 tions of the needle were far greater. With the same liquid, Smee's 

 battery gave the following results, obtained exactly as those already 

 described in section 15. 



Kind of wire Deflection, 



inserted. 



30^^' Soonfallsto 



28 



Copper 12.5 



28.5 



After a few vibrations — 



25. 



Copper 12 



25 



23 



