OF ELECTEIC SIGNALS THEOIJGH SUBMAEINE CABLES. 
991 
The dots first entered (Table IV.) appear as an even wavy line ; the lowest point of 
each wave is 10 parts, and the highest point 7^ parts below the dotted line, corre- 
sponding to the true ordinates from the base, viz. 40 and 42^. The top and bottom 
only of the waves are fixed by the observations. 
The second kind of signals are called dashes, because if sent through a short cable or 
air line, they would print a succession of dashes or lines, separated by short spaces 
equal to those separating dots sent at the same speed. To do this the contact with 
earth is made the same as for a dot, but the contact with the battery is made twice as 
long. Examples of the dash will be found in Tables VI. and XIII. 
The effect of combining these two primary signals was tried by sending alternate dots 
and dashes ; the results are entered in the Tables. The effect of one complete cycle of 
operations is shown in the figures annexed to the Tables by that part of the curve drawn 
with a thicker black line. Thus in the second dot and dash curve of Table IV. the dot 
curve begins with the ordinate 53-2 ; the first battery-contact slightly increases the 
current, till the ordinate of the top of the dot curve becomes 55 ’5. The first earth- 
contact diminishes the current, so that the ordinate at the end of the dot or beginning 
of the dash curve is 48’0 ; the next battery-contact, being a long contact, raises the dash 
curve to 61 ’7. The second earth-contact lowers it to 53‘2, when the cycle recommences. 
The numbers in the two last columns of the Tables IV., VI., XIII., and XIV., with 
the figures annexed, are all directly comparable, for they all represent the results reduced 
to a percentage, and are consequently constant for each length, being independent of 
any change in the battery. 
These observations do not give the retardations properly so called, i. e. they do not show 
the time separating the contact made at A from the effect produced at X, but they establish 
several conclusions of greater importance than the knowledge of this retardation. 
It will be seen (Table VI.) that when 66 dots per minute were sent into 1802 knots 
of cable at A, a constant current was received at X, in which no oscillation could be 
seen corresponding to the signals sent*. 
The same phenomenon was observed with 2192 knots in circuit, when more than 
50 dots per minute were sent. The effect produced at X by these rapidly repeated dots 
was almost exactly that which would have been observed if the cable at A had been 
permanently connected with a battery of about 30 cells. In moving the Morse key up 
and down, a little time elapses between the contact with earth and that with the battery, 
during which the cable is really insulated at A. This dost time caused the received 
current to be equal to only 41-6 in one case and 42’9 in the other instead of 50 per 
cent, of the maximum permanent current, as would certainly have been the case if the 
sums of the battery and earth contacts had respectively occupied exactly the half of each 
minute. 
* The immobility of the spot could not be accounted for by the inertia of the mirror and magnet, which, 
when in vibration, moved so rapidly that the oscillations could not be counted. Similar observations made 
with a galvanometer, the needle of which oscillated slowly, would lead to most erroneous results. 
