A charge, then, on the tubes or crystals purchased, and included in the purchase price paid by the owner of the receiving set, is the method here suggested for meeting the cost of broadcasting. Why these articles rather than any other should be taken as the criterion in laying the charge will appear from what follows. Two similar tubes giving identically the same service may not last each as long as the other. But in the long run, tubes of reputable manufacture in ordinary service will last a time closely enough concurrent with their usage to serve as a basis for the owner's share of the broadcasting he receives. With crystals the relation between use and useful life is not so satisfactory.
Crystals do in time lose their sensitivity as detectors and have to be discarded.
But statistics will be needed to determine accurately how long the different crystals now in use for radio reception may be expected to give satisfactory service before requiring replacement. No doubt considerable data on this subject is already available. In a tube set, the number of tubes is an excellent index of the cost of the set and of the range over which it can receive. Thus a broadcasting tax on tubes will affect more the owner of the expensive set who should be required to pay more, because he is able to command a broader choice of program than the owner of the less expensive set who is correspondingly less able to pay the larger tax. Crystal sets do not as a rule involve very expensive equipment and in any event their range is usually limited, and hence a sliding tax scale here is not particularly to be desired.