366 POPULAR SCIENCE MONTHLY. 



because the oscillations are damped out of existence too soon by the 

 dielectric. 



In arranging condensers to attain a given capacity, regard has to 

 be taken of the fact that for a given potential difference there must be 

 a certain total thickness of dielectric, and that if condensers of equal 

 size are being arranged in parallel, it adds to their capacity, whilst 

 joining them in series divides their capacity. If N equal condensers or 

 Ley den jars have each a capacity represented by C and if they are 

 joined n in series and m in parallel, the joint capacity of the whole 

 number is mC/n, where the product mn = N. 



Passing on next to the consideration of oscillation transformers of 

 various kinds — these are appliances of the nature of induction coils 

 for transforming the current or electromotive force of electrical oscil- 

 lations in a required ratio. These coils are however destitute of any 

 iron core, and they generally consist of coils of wire wound on a fiber, 

 wooden or ebonite frame, and must be immersed in a vat of oil to pre- 

 serve the necessary insulation. No dry insulation of the nature of 

 indiarubber or guttapercha will withstand the high pressures that are 

 brought to bear upon the circuits of an oscillation transformer. In 

 constructing these transformers, we have to set aside all previous 

 notions gathered from the design of low frequency iron core trans- 

 formers. The chief dijfficulty we have to contend against in the con- 

 struction of an effective oscillation transformer is the inductance of 

 the primary circuit and the magnetic leakage that takes place. In 

 other words, the failure of the whole of the flux generated by the 

 primary circuit to pass through or be linked with the secondary circuit. 

 Mr. Marconi has employed an excellent form of oscillation transformer, 

 in the design of which he was guided by a large amount of experience. 

 In this transformer the two circuits are wound round a square wooden 

 frame. The primary circuit consists of a number of strands of thick 

 insulated cable laid on in parallel, so that it consists of only one turn 

 of a stranded conductor. The secondary circuit consists of a number 

 of turns, say ten to twenty, of thinner insulated wire laid over the pri- 

 mary circuit and close to it, so that the transformer has the transforma- 

 tion ratio of one to ten or one to twenty. In the arrangements devised 

 and patented by Mr. Marconi, these two circuits, with their respective 

 capacities in series with them, are tuned to one another, so that the 

 time-period of each circuit is exactly the same, and without this tuning 

 the device becomes ineffective as a transformer.* There is no advan- 

 tage in putting a number of turns on the primary circuit, because such 

 multiplication simply increases the inductance, and, therefore, dimin- 

 ishes the primary current in the same ratio which it multiplies the 



* See British specification No. 7,777 of 1900 — G. Marconi, ' Improvements 

 in Apparatus for Wireless Telegraphy.' 



