SCIENTIFIC SUMMARY. 
131 
consists of varnished straight iron wires O'Oo inch diameter. The outer 
diameter of the coil is about 8 inches. The primary coil consists of two 
parallel insulated copper wires OT inch thick, and may be connected 
either as one wire of the total length, or as a double wire of half the 
length. The primary coil is surrounded by a cylinder of ebonite, which 
is thicker at its ends than at its middle, to resist the greater tension of the 
electricity at those parts. The secondary coil consists of 11,762 yards, or 
6 '83 statute miles, of insulated copper wire, of 0'006 inch diameter, and is 
wound upon the ebonite cylinder in 299,198 turns ; its total weight is 64 
pounds. The great power of the coil depends largely upon the arrange- 
ment of the secondary wire, which is as follows : — The space outside the 
ebonite cylinder is divided into 150 narrow and deep grooves, by means of 
thin, flat, annular discs of ebonite, which fit closely upon the cylinder ; 
the fine wire was wound into each of these adjacent spaces alternately in 
opposite directions, until they were all filled, connecting each section of 
wire at the bottom of the groove with its neighbouring section on one side, 
and at the top of the groove with its other neighbouring section on the other 
side, and so on throughout the entire series, so as to form one continuous 
wire. This separation of the secondary coil into numerous sections by a 
powerfully insulating material greatly increases the resisting power of the 
insulation; the plan also of winding each alternate section in opposite 
directions is also of great value in a similar aspect. The condenser con- 
sists of several discs of paper glued together, and covered with tin-foil, the 
surface of the two tin-foil coatings being equal to sixteen square feet each ; 
the condenser of this apparatus does not much affect the length of the spark, 
but is important to prevent the mercury of the break contact from being 
violently thrown about. Owing to the peculiar construction of this coil, 
greater effects are obtained with seven miles of secondary wire than had 
been previously obtained, in some other coils, with fifty miles; the leading 
principle of its construction appears to have been, to proportion the 
amount of resistance to the amount of tension in all its parts. 
Mr. Siemens also exhibited a new telegraphic instrument remarkable 
for rapid transmission of messages through long circuits : it is worked by 
means of magneto-electric currents, and each signal requires two currents; 
one positive and one negative, to produce it ; the code of signals is that 
known as “ Morse’s alphabet.” Eighty words per minute were transmitted 
through a resistance equal to 3,000 statute miles of underground wire. It 
is said that a speed of 400 letters per minute may.be accomplished, day 
and night continuously, by means of this instrument. 
M. Becquerell has exhibited to the French Academy of Sciences 
specimens of metals obtained by electrolysis, accompanied by a memoir 
describing the methods he adopted to obtain fine specimens of cobalt, 
nickel, silver, gold, and platinum. The plan he adopts is to decompose 
concentrated solutions of the respective metals by currents of very feeble 
intensity, thus avoiding tumultuous deposits, and enabling the molecules 
to group themselves regularly and firmly ; the intensity of the currents 
he employs varies with the density of the respective solutions. 
Mr. Gore has described, in the Pi’oceedings of the Royal Society, “ two 
additional kinds of electro-deposited antimony possessing the property of 
K 2 
