120 POPULAR SCIENCE MONTHLY. 



wave motion, and, being reflected as condensation at the closed end, 

 travel down again; and so after being reflected once or twice at the 

 open or closed end, become damped ont very rapidly in virtue of both 

 air friction and the radiation of the energy. In the case, however, of 

 the ordinary organ-pipe, we do not depend merely upon a store of com- 

 pressed air put into the pipe, but we have a store of energy to draw 

 upon in the form of the large amount of compressed air contained in 

 a wind chest, which is being continually supplied by the bellows. This 

 store of compressed air is fed into the organ-pipe with the result that 

 we obtain a continuous radiation of sound waves. The first case, in 

 which the only store of energy is the compressed air originally con- 

 tained in the pipe, illustrates the operation of the simple Marconi 

 aerial. The second case, in which there is a larger store of energy to 

 draw upon, the organ-pipe being connected to a wind chest, illustrates 

 the Marconi-Braun method in which an aerial is employed to radiate 

 a store of electric energy contained in a condenser, gradually liberated 

 by the aerial in the form of a series of electrical oscillations and waves. 

 In this arrangement the condenser corresponds to the wind chest, and 

 it is continually kept full of electrical energy by means of the induction 

 coil or transformer, which answers to the bellows of the organ. From 

 the condenser, electrical energy is discharged each time the spark dis- 

 charge passes at a spark gap in the form of electrical oscillations set 

 up in the primary circuit of an oscillation transformer. The secondary 

 circuit of this transformer is connected in between the earth and the 

 aerial, and therefore may be considered as part of it, and, accordingly, 

 the energy which is radiated from the aerial is not simply that which 

 is stored up in it in virtue of its own small capacity, but that which is 

 stored up in the much larger capacity represented by the primary con- 

 denser or, as it may be called, the electrical wind chest. By the second 

 arrangement we have therefore the means of radiating more or less con- 

 tinuous trains of electric waves, corresponding with each spark dis- 

 charge. To create powerful oscillations in the aerial, one condition 

 of success is that there shall be an identity in time-period between the 

 circuit of the aerial and that of the primary condenser. The aerial is 

 an open circuit which has capacity with respect to the earth, and it has 

 also inductance, partly due to the wire of the aerial and partly due 

 to the secondary circuit of the oscillation transformer in series with it. 

 The primary circuit or spark circuit has capacity, viz., the capacity 

 of the energy-storing condenser, and it has also inductance, viz., the 

 inductance of the primary circuit of the oscillation transformer. We 

 shall consider at a later stage more joarticularly the details of syntonis- 

 ing arrangements, but meanwhile it may be said that one condition 

 for setting up powerful waves by means of the above arrangement is 



