Of what use ...
It is the fate of the scientist to face the constant demand that he show his learning to have some "practical use." Yet it may not be of any interest to him to have such a "practical use" exist; he may feel that the delight of learning, of understanding, of probing the Universe is its own reward entirely. In that case he may even allow himself the indulgence of contempt for anyone who asks more.
Then he goes on to describe instances in the works of Plato, Faraday, Edison, Einstein etc ... discoveries that either their contemporaries or they themselves ignored as "useless", but later laid the foundations of modern technology. Obscure discoveries like the "Edison Effect" which was a by-product of the first electric lamp, and on which is based the whole domain of electronics.
And finally he says:
No one knows what's in it for you right now, any more than Plato knew in his time or Faraday knew, or Edison knew, or Einstein knew.
But you will know if you live long enough; and if not, your children or grandchildren will know. And they will smile at those who say, "But what is the use of sending rockets into space?" just as we now smile at the person who asked Faraday the use of his demonstration.
In fact, unles we continue with science and gather knowledge, whether it is seemingly useful on the spot or not, we will be buried under our problems and find no way out.
It is up to you then, and up to everyone, to support science and, where possible, to keep abreast of it, for today's science is tomorrow's solution - and tomorrow's problems, too - and most of all, mankind's greatest adventure, now and forever.