By a modification of the bridge method, applied with excellent results by Dr Muirhead to submarine work, condensers are substituted for a and b, one being also placed in the circuit between P and Q.
The apparatus consists of a sending battery B, a reversing transmitting key K, a slide of small resistance 5, three condensers C1, C2, C3, an artificial cable AC, the receiving instruments I and G, and one or more resistances R for adjusting the leakage current.
The conductor of the cable is practically insulated, as the condensers in the bridge have a very high resistance; hence no appreciable current ever flows into or out of the line.
After a very short interval of time, the length of which depends on the inductive retardation of the cable, the condensers corresponding to C 1 and C3 at the other end begin to be charged from the cable, and since the charge of C3 passes through the receiving instrument I or G the signal is recorded.
The charging of C3 at the receiving end will take place, no matter what is the absolute potential of the condensers, consequently the incoming signals are not affected by those which are being transmitted from that end.
When the key is released the condensers and cables at once begin to return to zero potential, and if the key is depressed and released several times in rapid succession the cable is divided into sections of varying potential, which travel rapidly towards the receiving end, and indicate their arrival there by producing corresponding fluctuations in the charge of the condenser C3.
A system by which the primary and secondary circuits were " turned " or syntonized by including condensers in the circuits.
In many cases additional condensers or inductance coils are inserted in various places so that the arrangement is somewhat disguised, but by far the larger part of the electric wave wireless telegraphy in 1907 was effected by transmitters having antennae either inductively or directly coupled to a closed condenser circuit containing a spark gap.
The oscillations are controlled either by a key inserted in the primary circuit of the exciting induction coil or transformer, or by a key cutting in and out of the primary condensers or throwing inductance in and out of the closed oscillation circuit.
The impedance of the primary or alternator circuit is so adjusted that when both the chokers are in circuit the current flowing is not sufficient to charge the condensers; but when one choker is short-circuited the impedance is reduced so that the condenser is charged, but the alternating arc is not formed.
Up to that time an induction coil known as a ro-inch coil had sufficed for spark production, but it was evident that much more power would be required to send electric waves across the Atlantic. Transformers were therefore employed taking alternating electric current from an alternator driven by an oil or steam engine, and these high tension transformers were used to charge condensers and set up powerful oscillations in a multiple antenna.
An improvement in this respect has been effected by the insertion of condensers in the cord circuits, coupled with the use of two sets of impedance coils, one set on each.
A cord circuit, similar in many respects, including the method .y.^9 Jr '' of operation, but equipped with condensers and impedance coils, in place of the repeating coil, is shown in fig.
Condensers are always required for underground pumps.
Pp. 98-148 (Breslau, 1905); also see Landolt and Bornstein's Tables of Physical Constants (Berlin, 1894) If we have a number of such condensers we can combine them in " parallel " or in " series."
If all the plates on one side are connected together and also those on the other, the condensers are j oined i n parallel.
If the condensers are so joined that the inner coating of one is connected to the outer coating of the next, they are said to be in series.
These rules provide means for calculating the resultant capacity when any number of condensers are joined up in any way.
On the other hand there are numerous methods by which the capacities of condensers may be compared and a relative measurement made in terms of some standard.
The two condensers to be compared are connected in the branches of a Wheatstone's Bridge and the other two arms R deter- completed with variable resistance boxes.
It depends on the principle that if two condensers of capacity C I and C2 are respectively charged to potentials V I and V2, and then joined in parallel with terminals of opposite charge together, the resulting potential difference of the two condensers will be V, such that V = (C,V 2 -CiV2) /(C1+C2) (16); and hence if V is zero we have C I: C2 = V2 The method is carried out by charging the two condensers to be compared at the two sections of a high resistance joining the ends of a battery which is divided into two parts by a movable contact.'
This contact is shifted until such a point is found by trial that the two condensers charged at the different sections and then joined as above described and tested on a galvanometer show no charge.
A simple method for condenser comparison is to charge the two condensers to the same voltage by a battery and then discharge them successively through a ballistic galvanometer and observe the respective " throws " or deflections of the coil or needle.
He constructed two equal condensers, each consisting of a metal ball enclosed in a hollow metal sphere, and he provided also certain hemispherical shells of shellac, sulphur, glass, resin, &c., which he could so place in one condenser between the ball and enclosing sphere that it formed a condenser with solid dielectric. He then determined the ratio of the capacities of the two condensers, one with air and the other with the solid dielectric. This gave the dielectric constant K of the material.
Soc., 1880, 30, p. 411, showing experiments on residual charge of condensers and a comparison between the behaviour of dielectrics and glass fibres under torsion.
Six condensers yield 52,000 gal.
Count Gramont 5 has been able to obtain spectro scopic evidence of the metalloids in a mineral by employing powerful condensers and heating the electrodes in an oxyhydro gen flame when these (as is often the case) are not sufficiently conducting.
To produce the alkali metal, a calcined mixture of sodium carbonate, coal and chalk was strongly ignited in flat retorts made of boiler-plate; the sodium distilled over into condensers and was preserved under heavy petroleum.
Lothian, May 26 1848 and was educated at University College school, London, passing on to University College, whence he subsequently graduated B.Sc. with honours in chemistry in 1868-9, but before doing so he entered his father's works and there invented a method of testing condensers, afterwards widely accepted.
In other cases, Leyden jars or condensers take the form of sheets of mica or micanite or ebonite partly coated with tin foil or silver leaf on both sides; or a pile of sheets of alternate tin foil and mica may be built up, the tin foil sheets having lugs projecting out first on one side and then on the other.
For the purposes of wireless telegraphy, when large condensers are required, the ordinary Leyden jar occupies too much space in comparison with its electrical capacity, and hence the best form of con denser consists of a number of sheets of crown glass, each partly coated on both sides with tin foil.
It has been found, however, that very efficient condensers can be made with compressed air as dielectric. If a number of metal plates separated by small distance pieces are enclosed in an iron box which is pumped full of air to a pressure, say, of 10o lb.
Condensers of this kind have been employed by R.
Fessenden in wireless telegraphy, and they form a very excellent arrangement for standard condensers with which to compare the capacity of other Leyden jars.
Fessenden, "Compressed Air for Condensers," Electrician, 1905, 55, p. 795; Moscicki, "Construction of High Tension Condensers," L'Eclairage electrique, 1904, 41, p. 14, or Engineering, 1904, p. 865.
Cavendish measured the capacity of disks and condensers of various forms, and proved that the capacity of a Leyden pane is proportional to the surface of the tinfoil and inversely as the thickness of the glass.