|Hutton, Charles Mathematical and Philosophical Dictionary 1795|
way of combining them, so as to compose some such instrument as our Telescope: and his son, Samuel Molyneux, asserts more positively, that the invention of Telescopes, in its first original, was certainly put in practice by an Englishman, friar Bacon; although its first application to astronomical purposes may probably be ascribed to Galileo. The passages to which Mr. Molyneux refers, in support of Bacon's claims, occur in his Opus Majus, pa. 348 and 357 of Jebb's edit. 1773. The first is as follows: Si vero non sint corpora plana, per quæ visus videt, sed sphæria, tunc est magna diversitas; nam vel concavitas corporis est versus oculum vel convexitas: whence it is inferred, that he knew what a concave and a convex glass was. The second is comprised in a whole chapter, where he says, De visione fracta majora sunt; nam de facili patet per canones supra dictos, quod maxima possunt apparere minima, et e contra, et longe distantia videbuntur propinquissime, et e converso. Nam possumus sic figurare perspicua, et taliter ea ordinare respectu nostri visus et rerum, quod frangentur radii, et flectentur quorsumcunque voluerimus, ut sub quocunque angulo voluerimus, videbimus rem prope vel longe, &c. Sic etiam faceremus solem et lunam et stellas descendere secundum apparentiam hic inferius, &c: that is, Greater things than these may be performed by refracted vision; for it is easy to understand by the canons above mentioned, that the greatest things may appear exceeding small, and the contrary; also that the most remote objects may appear just at hand, and the converse; for we can give such figures to transparent bodies, and dispose them in such order with respect to the eye and the objects, that the rays shall be refracted and bent towards any place we please; so that we shall see the object near at hand or at a distance, under any angle we please, &c. So that thus the sun, moon, and stars may be made to descend hither in appearance, &c. Mr. Molyneux has also cited another passage out of Bacon's Epistle ad Parisiensem, of the Secrets of Art and Nature, cap. 5, to this purpose, Possunt etiam sic figurari perspicua, ut longissime posita appareant propinqua, et è contrario; ita quod ex incredibili distantia legeremus literas minutissimas, et numeraremus res quantumquo parvas, et stellas faceremus apparere quo vellemus: that is, Glasses, or diaphanous bodies may be so formed, that the most remote objects may appear just at hand, and the contrary; so that we may read the smallest letters at an incredible distance, and may number things though never so small, and may make the stars appear as near as we please.
Moreover, Doctor Jebb, in the dedication of his edition of the Opus Majus, produces a passage from a manuscript, to shew that Bacon actually applied Telescopes to astronomical purposes: Sed longe magis quam hæc, says he, oporterel homines haberi, qui bene, immo optime, scirent perspectivam et instrumenta ejus—quia instrumenta astronomia non vadunt nisi per visionem secundum leges istius scientiæ.
From these passages, it is not unreasonable to conclude, that Bacon had actually combined glasses so as to have produced the effects which he mentions, though he did not complete the construction of Telescopes. Dr. Smith, however, to whose judgment particular deference is due, is of opinion that the celebrated friar wrote hypothetically, without having made any actual trial of the things he mentions: to which purpose he observes, that this author does not assert one fingle trial or observation upon the sun or moon, or any thing else, though he mentions them both: on the other hand, he imagines some effects of Telescopes that cannot possibly be performed by them. He adds, that persons unexperienced in looking through Telescopes expect, in viewing any object, as for instance the face of a man, at the distance of one hundred yards, through a Telescope that magnifies one hundred times, that it will appear much larger than when they are close to it: this he is satisfied was Bacon's notion of the matter; and hence he concludes that he had never looked through a Telescope.
It is remarkable that there is a passage in Thomas Digges's Stratioticos, pa. 359, where he affirms that his father, Leonard Digges, among other curious practices, had a method of discovering, by perspective glasses set at due angles, all objects pretty far distant that the sun shone upon, which lay in the country round about; and that this was by the help of a manuscript book of Roger Bacon of Oxford, who he conceived was the only man besides his father (since Archimedes) who knew it. This is the more remarkable, because the Stratioticos was first printed in 1579, more than 30 years before Metius or Galileo made their discovery of those glasses; and therefore it has hence been thought that Roger Bacon was the first inventor of Telescopes, and Leonard Digges the next reviver of them. But from what Thomas Digges says of this matter, it would seem that the instrument of Bacon, and of his father, was something of the nature of a camera obscura, or, if it were a Telescope, that it was of the reflecting kind; although the term perspective glass seems to favour a contrary opinion.
There is also another passage to the same effect in the preface to the Pantometria of Leonard Digges, but published by his son Thomas Digges, some time before the Stratioticos, and a second time in the year 1591. The passage runs thus: My father by his continuall painfull practises, assisted with demonstrations mathematical, was able, and sundrie times hath by Proportional Glasses duely situate in convenient angles, not only discovered things farre off, read letters, numbered peeces of money with the very coyne and superscription thereof, cast by some of his frecnds of purpose upon downes in open fields, but also seven myles off declared what hath beene doone at that instant in private places: He hath also sundrie times by the sunne beames fixed (should be fired) powder, and dischargde ordinance halfe a mile and more distante, &c.
But to whomsoever we ascribe the honour of first inventing the Telescope, the rationale of this admirable instrument, depending on the refraction of light in passing through mediums of different forms, was first explained by the celebrated Kepler, who also pointed out methods of constructing others, of superior powers, and more commodious application, than that first used: though something of the same kind, it is said, was also done by Maurolycus, whose treatise De Lumine et Umbra was published in 1575.
The Principal Effects of Telescopes, depend upon this plain maxim, viz, that objects appear larger in proportion to the angles which they subtend at the