Laws of the Elementary Voltaic Battery. 53 



16. An examination of Ritchie's Law of Surface. 

 Reasoning from some of the foregoing experiments where a dim- 

 inution of action accompanied an increase of the zinc surface, and 

 where also, the increase of power from augmentation of the copper 

 surface, still fell far short of being proportional to the quantity of that 

 metal immersed, we were naturally induced to doubt, whether the 

 law announced by Dr. Ritchie, that the deflexion increases exactly 

 in the ratio in which the surfaces of the two metals are increased, 

 could be true.* 



The slips were of the same kind as before. Both were immersed 

 to equal depths. Intervals of five minutes were allowed between 

 the immersions, to permit the plates to regain their greatest energy. 

 Both 1 inch. 2 inch. 4 inch. 



1st. efl'ect, +200° +300° -400° 



V 60 85 170 



2' 61 82 J 15 



3' 61 82 • 115 



Repeated after an interval of 5 minutes ; beginning with 4 inches, 

 and diminishing to 1 inch. 



• In Vol. I. p. 33 of the Journal of the Royal Institution, Dr. Ritchie describes his 

 experiment and views in regard to this point in the following words. " Take two 

 rectangular slips of copper and zinc, an inch broad and eight or ten inches long, and 

 divide them into square inches by narrow bands of wax or cement. Solder copper 

 wires to their extremities, and fix them into a small frame so that they may always 

 he placed at the same distance from each other. Immerse them in a small vessel 

 of water, containing a small quantity of sulphuric acid, to the first horizontal divis- 

 ion ; turn round the torsion key till the untwisting force of the glass thread, balan- 

 ces the deflecting power of the electric current, and note the number of degrees of 

 torsion. Immerse them to the second division, turn round the torsion key as before, 

 and the degrees of torsion necessary to balance the deflecting force of the current, 

 from two square inches, will be found double of those for one square inch. Repeat 

 the experiment with three, four, &c., square inches, and the degrees of torsion will 

 be found proportional to the surface of the plates immersed. 



" Having thus shewn experimentally the accuracy of the instrument" — &c. 



From the last sentence it would appear that the truth of this law was already ad- 

 mitted, and that the experiments quoted above were made not so much to establish 

 it as to test the accuracy of the galvanometer by it. Now no one who reflects upon 

 the beautiful principle of torsion used in this instrument can doubt the correctness 

 of its indications when employed with the requisite precautions ; we do not think 

 however that in the case above cited, it could be regarded as fufnishing proof of the 

 truth of the law in question, for, as we have proved in our experiments upon first 

 effects, the adequate precautions were overlooked. 



The investigations which follow, go we think to establish, that no such law pre- 

 vails. 



