Electrical Wave or Current through a Metallic Circuit. 287 



majrnet. The local battery was therefore increased or de- 

 creased in power until the armature time, as recorded by the 

 two circuits, was identical in value; — the pen being so adjusted 

 that the primary dot was always followed by the second, or 

 vibrating dot, which was distinctly recorded by the pen in 

 every record made. 



These difficulties being thus overcome, the pens were ad- 

 justed to produce radiating dots, the disc being quiescent. It 

 was subsequently found that this adjustment was imperfect to 

 eleven thousandths of a second of time on the greatest circum- 

 ference recorded. The absolute space was laid off on all the 

 remaining circumferences, and, being accurately measured, 

 gives the required correction. 



All the arrangements having been perfected, the local con- 

 nexions were placed in the care of Mr. Henry Twitchell, 

 while it was assisted in the distant connexions by Mr. Stager, 

 of the O'Rielly Telegraph Office, Cincinnati. 



The evening was fair and calm, warm for the season. Mr. 

 Stager reported the line in admirable working order. The 

 receiving magnet was adjusted to its minimum working pass, 

 and the long and short circuit batteries were pronounced equal 

 in strength, by the equality of the recorded armature times. 



At 9^1 58™ the pens fell together on the metal plate, the va- 

 riable pen being operated on by the long circuit. I watched 

 the disc to see that the records were perfectly made. The 

 dots came down in the most beautiful manner, and the record 

 was engraved on the metal with exquisite delicacy. At the 

 close of the first circumference of dots, occupying exactly sixty 

 seconds, notice was given to change; and, at the word, the 

 long circuit was thrown off, and the local short circuit took 

 its place. This change was so skilfully accomplished by Mr. 

 Stager, that not a second was lost. 



In this way five complete circumferences were recorded, — 

 three with the long, and two with the short circuit. The ear 

 could sometimes with difficulty recognize the change from 

 long to short ; but after many trials it was found that this 

 organ could not with certainty be relied on. The conversion 

 of time into space on the disc gave us, however, the opportu- 

 nity of bringing a high magnifying power to bear upon the 

 reading of the delicate records. 



Mr. Twitchell has completed all the measures with the in- 

 strument contrived by me for measuring small angular spaces. 

 It can be read down to the thousandth of a second of time. 

 The disc performed in the most admirable manner during the 

 entire experiment, the records radiating from its centre, and 

 demonstrating the uniformity of its motion. 



I present the measures of circumferences Nos. 1 and 2, to 



