37 6 Natural Magick. 17.

t faat the immense goodness of our great God may be praised, and adored. Becausea proportional Radius doth proceed from the greater Section, from the less is madethe greater: to avoid this, make it of a Cylindrical Section, for it is the mean, andlet it be set for the axis of the small and of the greater dissection, which may passthrough the middle parallels: this held against the Son, doth make refraction of thebeams sent into it, very far, and perpendicularly from the Centre of a Cylindri-cal Section ; and in this Art the reason cannot be found , that the beams uniungshould part again: Wherefore it receives them directly, which it sends back againobliquely into beams far from the superficies of it. For the beams pasting throughthe narrow hole of a window, are forthwith dilated ; nor is their proportion kept,by being far removed , therefore it may reverberate and burn where the Cane seemsclearest , which will be neer the Centre , nor is it fardistabt from the point wherethe rays meet; but neer the ray coming forth from that point, from the superficiesof the Glass, called Parabolicall , which must remain firm in that place which I saidbefore. Let experiment be made of its venue, by threds pasting from its Centre,or iron wire, or hair; and it is no matter whether it be Parabolical or Spbarrical, orany Section of the fame order: then let it be excellent well fitted upon the Centreof the said Section: If the rays go forth above, or a little beneath, it is no matter,if not much money, or much money be laid out to make it. The making of it de-pends mcerly on the Artificers hand ; the quantity is nothing, be it small or great.The Latitude of the hollow is not necessary, oncly let it be sent forth from the mid-dle, that the rays may meet excellent well in the Centre. Let the window be madeopen asljunt, that it may receive a Parabolical Glass; and thus shall you have aGlass, if that be Well done I spake of. He that hath ears to hear , let him hear • I havenot spoken barbarously , nor could I speak more briefly, or more plainly. But if asmall one do not answer a great one in proportion, know that you will operate no-thing: let it be large about the basis, small at the top, equidistant to the first. Letit nor be a steel Glass, because it cannot sustain the heat of the burning, and by burn-ing it losctb its brightness. Let it be therefore of Glass a finger thick: Let theTin foil be of purged Antimony, and Lead, such as they make in Germany: let theform be of day : put the Glass upon it, and melt it in a Glass furnace, that it may

take its form. This is a wonder, that thatwhich causeth so much burning in the work,is cold, or at most but lukewarm. If youwould have it burn before, of the Sectionwhich is about the basis, make a circle, inthe middle point whereof fir the Artifice,that the ray returning, may come forth tothe fore part. This I have said; and I haveobserved, that we may use this Artifice ingreat and wonderful things, and chiefly byinscribing letters in a full Moor. For what-soever we have written by this Glass, as Isaid of a plain Glass, we may fend letters ofit to a very great distance: and because I saidit sends forth to infinite distance, it is sent asfar as the Moon, especially being helped byits light.

Chap. XVIII.

To masse a Burning-Glass of many Spharical SeBions,

~\TItelho describes a certain composition of a Burning-glass, made of diversSphæraiSections : but what he writes he proves not, nor doth he understand what hefays: whilst I was searching for that, I found this. Propound the distance of com-bastion, let it be C B, let it be doubled, C A (hall be the semidiamiter of the Sph««»

whose