Page:In the high heavens.djvu/142

 so easy to exaggerate the capabilities of our great telescopes that it may be well to recount what is the very utmost that could be expected from even our greatest instrument when applied to the study of Mars. Let us consider, for example, the capabilities of the Lick telescope in aiding such an inquiry as that before us. This instrument, both from its position and its optical excellence, offers a better view of Mars at the present time than can be obtained elsewhere. But the utmost that this telescope can perform in the way of rendering remote objects visible is to reduce the apparent distance of the object to about one-thousandth part of its actual amount. Some, indeed, might consider that even the Lick instrument would not be capable of giving so great an accession to our powers as this statement expresses. However, I am willing to leave the figure at this amount, only remembering that if I estimated the powers of the telescope less highly than these facts convey, the argument on which I am entering would be correspondingly strengthened.

As we have already said, Mars is at a distance of 35,000,000 miles during a favourable opposition, and if we look at it through a telescope of such a power as we have described the apparent distance is reduced to one-thousandth part. In other words, all that the best telescope can possibly do is to exhibit the planet to us as it would be seen by the unaided eye if it were brought within a distance of 35,000 miles. This will demonstrate that even our greatest telescopes cannot be expected to enable us to answer the questions that are so often asked about our neighbouring globe. What could we learn of Europe if we had only a bird's-eye view of it from a height of