For a day or two after it was again put into operation Margaret and Roland could scarcely tear themselves away from it long enough for necessary sleep and meals, and several persons connected with the Works were frequently permitted to witness its wonderful operations.
Down, down descended that cylinder of light, until it had passed through all the known geological strata in that part of New Jersey, and had reached subterranean depths known to Clewe only by comparison and theory.
The apparent excavation had extended itself down so far that the disk at the bottom, although so brightly illuminated, was no longer clearly visible to the naked eye, and was rapidly decreasing in size on account of the perspective.

But the telescopes which Clewe had provided easily overcame this difficulty.

He was sure that it would be impossible for his light to penetrate to a depth which could not be made clearly visible by his telescopes.
It was a wonderful and weird sensation which came over those who stood, glass in hand, and gazed down the track of the Artesian ray.

Far, far below them they saw that illuminated disk which revealed the character of the stratum which the light had reached.

And yet they could not see the telescope which they held in their hands; they could not see their hands; they knew that their heads and shoulders were invisible.