They are not only strictly local but exhaustible; though,at a given place and time,they may exist in much greater abundance than would be applied to present use even if they could be obtained gratis.

• 它们不仅严格地局限于某些地点，而且是可耗尽的，不过在某一地点和时间，即令可无偿得到它们，它们的储量也会远远超过所需的数量。