Christiani Hugenii Const. F. Astroscopia Compendiaria, Tubi Optici molimine liberata

ASTROSCOPIA COMPENDIARIA. 13

For behold, while I write this, I am informed by Cassini’s letters that four lenses, the largest of which is intended for a telescope of one hundred and forty feet, have been completed at Rome by Giuseppe Campani and are most excellent, and have been sent to the great King of France. For although they have not yet been applied to the observation of celestial bodies, it is not to be doubted that their examination was conducted during the day in long halls or porticoes from which light was excluded. But now, with this invention of ours, its utility will be established both for these lenses and if any exceed these in length.

But if we think about the ways in which others have sought to increase the efficiency of telescopes, it may seem that we have achieved with this slight labor what they sought in vain. For whether they have attempted this through hyperbolic or elliptic figures of lenses, as Descartes did, or through concave mirrors, as Newton did, or by any other reason, everything returned to this: that in shorter telescopes, and those used with less effort, the things seen would be greatly magnified. For neither could that accurate and scrupulous shaping of surfaces be avoided, nor the size of the lenses or mirrors, since it is necessary that whatever we have devised be rendered useless by excessive obscurity unless the apertures through which the light first enters grow in proportion to the perceived magnification. We, however, have not decreased the lengths, but we have made it so that they do not hinder, which amounts to almost the same thing.

If anyone now asks how far I believe telescopes can be extended and at what cost of labor, and whether, having produced them far beyond the measure of what we said a little while ago, we should hope that we will still approach the moon and other stars ten times closer than we have proceeded with those having thirty feet—by which, of such a journey, one hundred and forty-nine parts have been completed, with only one remaining—I will answer that I cannot predetermine certain limits for the art; yet, that it will not be reached by the greatest human effort, and much less will it happen, as some seem not to have despaired, that we might inspect the moon and the other planets as if from nearby, and penetrate with our vision whether they are inhabited by animals, or whether they have nothing beyond vast solitudes.