There are passages in the work 'De Secretis Operibus,' &c. (cited by Hutton, 'Dictionary,' article "Gunpowder"), which expressly mention sulphur, charcoal, and saltpetre as ingredients. But, independently of the claim of the Chinese and Indians, there is an author, Marcus Graecus, whose work, 'Liber Ignium' (now existing only in Latin translations from the Greek), is cited by Dr. Jebb from a manuscript in the possession of Dr. Mead, and who appears to have been considered by both as older than Bacon. Dr. Hutton, into whose hands Dr. Mead's manuscripts passed, found this writer mentioned by an Arabic physician of the ninth century. Graecus gives the receipt for gunpowder, namely, one part of sulphur, two of willow-charcoal, and six of saltpetre. Two manuscript copies of Graecus were also found in the Royal Library of Paris. But it does not appear that Graecus was known for a long time after Bacon: even Tartaglia knew nothing of him; for he says, in his work on Artillery, that the oldest writers known to him use equal parts of the three ingredients. With regard to the telescope, it must be admitted that Bacon had _conceived_ the instrument, though there is no proof that he carried his conception into practice, or _invented_ it. His words are these:--"We can so shape transparent substances, and so arrange them with respect to our sight and objects, that rays can be broken and bent as we please, so that objects may be seen far off or near, under whatever angle we please; and thus from an incredible distance we may read the smallest letters, and number the grains of dust and sand, on account of the greatness of the angle under which we see them; and we may manage so as hardly to see bodies, when near to us, on account of the smallness of the angle under which we cause them to be seen: for vision of this sort is not a consequence of distance, except as that affects the magnitude of the angle. And thus a boy may seem a giant, and a man a mountain, &c." The above contains a true description of a telescope; but if Bacon had constructed one, he would have found that there are impediments to the indefinite increase of the magnifying power; and still more that a boy does not appear a giant, but a boy at a smaller distance.