ELECTRO-TINT 251 



not, however, bo passed more quickly through the four cables than through one cable, 

 for, although the resistance has been reduced to one-fourth, the induction has been 

 quadrupled at the same time, which will exactly counterbalance the smaller resistance. 

 If the cables are merged into one, the case will then be altered, for the surface will at 

 once be brought down to one-half, and therefore there will only be half the amount of 

 induction to retard the rapidity of signalling, whilst the conducting power will remain 

 the same as it was before. As the outer surface of the gutta-percha does not increase 

 so rapidly as its substance, there will be a gain on that head, for if the conductor is 

 -jth of an inch in diameter, and it is coated to the depth of ^th of an inch with gutta- 

 percha, making a total diameter of y^ths of an inch, the united exterior surface of four 

 such cables would be 3'6 square inches, but if the four conductors are merged into one, 

 the exterior surface will be 1'2 square inch, or less than half the exterior surface of the 

 four cables, in the proportion of 4 to 6. 



' The next question which has to be considered is whether the rate of transmission of 

 signals is affected by increasing the number of cells, when a voltaic battery is employed. 

 The author is of opinion that this would be the case. It has already been explained 

 how the wave of electricity rises and falls on connecting and disconnecting a battery 

 from a submarine circuit. The effect of a higher intensity would be to raise the wave 

 to its maximum height more quickly, and as the arrival of the current takes place at 

 the instant when the wave has risen sufficiently high at the further extremity to record 

 itself on the instrument, and not at the time it actually begins to flow, this height 

 would be attained more quickly, and signals also would be obtained sooner. An ex- 

 periment made by the Atlantic Telegraph Compiny seems inadvertently to prove the 

 truth of this reasoning. A Lilliputian battery of seven cells, reduced to the smallest 

 dimensions, having been connected to a cable 600 miles long, the signals occupied ^ths 

 of a second in arriving. This battery was then disconnected, and another joined up 

 in its place, but of twelve cells, and with a much larger extent of surface in each cell, 

 when signals arrived in ^thsof a second. This great difference of speed is almost in 

 regular proportion to the number of cells employed. Had the signals, in the case of 

 the battery of seven cells, occupied ^ths, instead of 



a second in arriving, the 



speed would have been exactly in proportion to the number of cells, one cell taking 

 igths, seven cells occupying ^ths, and twelve cells a little more than ^ths of a second 

 in arriving. When it is remembered that no two cells of batteries differently con- 

 structed will have precisely the same intensity, even supposing these minute differences 

 of time were quite accurately recorded, there would still be reasons sufficient to account 

 for the irregularity. It should be mentioned that this experiment is stated to be given 

 in order to show that increasing the battery surface alone, affects the rate of transmis- 

 sion. No explanation of how it does this is attempted, and the difference in the 

 intensity of the two batteries seems to have been overlooked as a matter of no impor- 

 tance. The author believes the increase of rate to have been chiefly due to the larger 

 number of cells employed in the second part of the experiment, and not so much to the 

 increased surface. He has already explained the conditions under which an increased 

 battery-surface would raise the tension of the current, and so increase the rapidity of 

 signalling. In this experiment the tension of the currents used was so low, and the 

 resistance opposed by the 600 miles of wire so great, that it is probable a very much 

 smaller dynamic quantity was generated through the whole length of the wire than 

 even the Lilliputian battery would generate through a circuit of nominally no resis- 

 tance. If this was the case, increasing the battery surface only, without adding to the 

 series, would have but little effect in increasing the quantity flowing. The experiment, 

 therefore, as a trial of the effect of large battery-surface alone, cannot be considered a 

 fair one. Attention has been drawn to it here, as it may help to throw some light 

 upon the matter under consideration.' 



The following note of a gold-leaf electrometer, and the introduction of an induction 

 coil, promises to give increased sensibility. It is the invention of Mr. Highton, who 

 introduces an induction coil, the especial object of which is to multiply the current at 

 the receiving end of a telegraphic line. This recording instrument is also a novelty, 

 and consists of a strip of gold-leaf, about an inch and a half in length, and weighing 

 Y^jgth parts of a grain, suspended between the two poles of an electrometer. Near the 

 leaf is a magnet which causes the leaf to be deflected, either to the right hand or to the 

 left, according as a positive or negative current is brought into action. The vibra- 

 tions of the leaf are magnified by an ordinary magic-lantern arrangement, and are 

 thrown on a screen, from which they are read off by the operator. 



ELECTRO-TINT. The art of preparing tinted plates by the action of electricity % 

 on copper. One process consists in putting a perfectly clean copper plate into a 

 solution of acetate of lead, and making it one of the terminal poles of a voltaic battery, 

 the other pole being a piece of pure lead dipping into the solution. Tints of the 



