636 Transactions of the American Institute. 



net, reflects a spot of light on a distant scale, where by its oscilla- 

 tions the spot of light indicates movements of the magnet too small 

 to be seen. The little swinging magnet follows every change in 

 the received current, and every wave, great or small, produces a 

 corresponding oscillation on the spot on the scale. These oscilla- 

 tions, produced in due order, are easily read by a practiced clerk — 

 no one knew how easily. The sending arrangements were designed 

 to produce perfect regularity in these little waves, making them as 

 sharply defined as possible; but just as by a practiced eye hand- 

 writing can be read in which there is no single clearly-formed letter, 

 60 it has been found a clever clerk will instinctively, as it were, disen- 

 tangle the most irregular oscillations of the little spot of light into 

 letters and words they should represent; and from this cause the 

 greater part of the sending gear has been found unnecessary, and 

 yet the bold estimate of eight words per minute has been exceeded. 

 The addition of a single simple little instrument allows four timea 

 the number of words to be sent through the Atlantic that could be 

 sent through the Malta-Alexandria cable, of little more than two- 

 thirds the length. Here, then, is at least as great an advance as in 

 other branches of submai'ine telegraphy. In future long cables the 

 speed may be calculated on this new basis, which' has long been 

 advocated by a few, but which had not received practical confirma- 

 tion till now. The speed at which messages can be sent through a 

 given length of cable is simply proportional to the quantity of 

 copper and gutta-percha used, provided the relative proportions 

 of these materials remain unchanged, as is now practically true in 

 most cases. 



The signaling arrangements connected with the Atlantic cable 

 present this peculiarity, that there is no voltaic circuit. The cur- 

 rent is received at Valentia in a Leyden jar or condenser, which 

 acts as a sort of elastic reservoir. When receiving, it is alternately 

 charged by the cable and discharged back into the cable; while 

 the galvanometer, placed between the condenser and the cable, indi- 

 cates the alternate forward and backward tide in the current. 

 Similarly when Valentia wishes to send signals, it charges the con- 

 denser positively or negatively, by the induction from the battery, 

 and thus causes corresponding movements in the charge of the 

 cable. This arrangement is due, we believe, to Mr. Varley, and 

 prevents, to a great extent, the action of earth currents, which 

 would otherwise be found troublesome with so sensitive an instru- 

 ment as the mirror galvanometer. 



