for Voltaic Electricity. 



199 



2. The graduated card at the top was enlarged to five inches 

 diameter, and carefully graduated to degrees ; and by an index 

 traversing this card_, the degrees of torsion necessary to bring the 

 deflected needle vertical to the black mark on the lower card was 

 read off easily to a fraction of a degree. 



3. The graduated plate turned on its own axis independently 

 of the axis of the glass thread, rendering the adjustment of the 

 needles easy and perfect. 



4. The needles were considerably increased in size and highly 

 magnetized 



With these alterations the action of the galvanometer was cer- 

 tain and delicate, returning after even a deflection of a thousand 

 degrees, or three times round the card, with certainty to the 

 index mark on the lower card ; and the same experiment repeated 

 corresponding to the fraction of a degree. 



The battery used was my gas-carbon battery, and the follow- 

 ing means were adopted to keep it constant. 



1. The nitric acid cell was filled with the acid of commerce, 

 but the zinc cell only half-filled with dilute sulphuric acid. 



2. The prism of carbon was suspended at its top to a rack- 

 work, by which its immersion to a greater or less depth was 

 regulated ; consequently any required amount of electricity ob- 

 tained. 



With these precautions a constant current of electricity was 

 maintained for hours ; rarely varying, after efi'ecting a torsion of 

 three or four hundred degrees, one degree for hours. By this 

 means also, at all times the same amount of current could be 

 obtained, rendering it easy to recommence the experiments. 



Table I. — Battery power 400. Each wire was No. 20. 



P2 



