Part 13 (1/2)
The Contents.
_Monsieur de _Sons_ progress in working _Parabolar_ Gla.s.ses. Some speculations of Monsieur _Auzout_ concerning the changes, likely to be discovered in the Moon. The instance of the same Person to Mr. _Hook_, for communicating his Contrivance of making with Gla.s.ses of a few feet Diameter, _Telescopes_ drawing several hundred feet; together with his Offer of recompensing that secret with another, which teaches, How to measure with a _Telescope_ the _Distances of Objects_ upon the _Earth_.
The Experiment of _Kircher_, of preparing a Liquor, that shall sink into, and colour the whole Body of Marble, delivered at length. An Intimation of a Way found in _Europe_, to make good _China-Dishes_. An Account of an odd Spring in _Westphalia_, together with an Information touching _Salt-Springs_; and a way of straining _Salt-water_. Of the Rise and Attempts of a way to conveigh Liquors immediately into the Ma.s.s of Blood._
_Of Monsieur _de Sons_ Progress in working _Parabolar_ Gla.s.ses._
Since what was mentioned in the immediately precedent _Tract_, touching Monsieur _de Son's_ n.o.ble attempt of grinding Gla.s.ses of a _Parabolical_ Figure, the _Publisher_ of these _Papers_ hath himself seen two _Eye-gla.s.ses_ of that shape, about one inch & a half deep, and one inch and a quarter broad, wrought by this Eminent _Artist_ with a rare Steel-instrument of his own contrivance and workmans.h.i.+p, and by himself also polished to admiration. And certainly it will be wondred at by those, {120} who shall see these Gla.s.ses, how they could be truly wrought to such a Figure, with such a Cavity; & yet more, when they shall hear the Author undertake to excavate other such _Eye-Gla.s.ses_ to above two inches, and _Object-gla.s.ses_ of five inches _Diameter_. He hath likewise already begun his _Object-gla.s.ses_ for the mentioned two _Ocular_ ones, of the same Figure of about two inches _Diameter_, which are to be left all open, yet without causing any colours. Of all which 'tis hoped, that shortly a fuller and more particular accompt will be given.
_Monsieur _Auzout's_ Speculations of the Changes, likely to be discovered in the _Earth_ and _Moon_, by their respective Inhabitants._
This Inquisitive _Philosopher_ in a letter of his, lately written to his correspondent in _London_, takes occasion to discourse of his considerations concerning those Changes, mentioned in the _t.i.tle_, as followes;
I have (saith he) sometimes thought upon the _Changes_, which 'tis likely, the supposed Inhabitants of the _Moon_ might discover in our _Earth_, to see, whither reciprocally I could observe any such in the _Moon_. For example, methinks, that the _Earth_ would to the people of the _Moon_ appear to have a different face in the several seasons of the year; and to have another appearance in _Winter_, when there is almost nothing green in a very great part of the _Earth_; when there are Countries all covered with snow, others, all covered with water, others, all obscured with Clouds, and that for many weeks together: _Another_ in _Spring_, when the Forrests and Fields are green. _Another_ in _Summer_, when whole Fields are yellow &c.
Me thinks, I say, that _these_ changes are considerable enough in the force of the reflexions of Light to be observed, since we see so many differences of Lights in the _Moon_. We have _Rivers_ considerable enough to be seen, and they enter far enough {121} into the Land, and have a bredth capable to be observed. There are _Fluxes_ in certain places, that reach into large Countries, enough to make there some apparent change; & in some of our Seas there float sometimes such bulky ma.s.ses of Ice, that are far greater, than the Objects, which we are a.s.sured, we can see in the _Moon_. Again, we cut down whole Forrests, and drain Marishes, of an extent large enough to cause a notable alteration: And men have made such works, as have produced Changes great enough to be perceived. In many places also are _Vulcans_, that seem big enough to be distinguish't, especially in the shadow: And when Fire lights upon Forrests of great extent, or upon Towns, it can hardly be doubted, but these Luminous Objects would appear either in an Ecclipse of the Earth, or when such parts of the Earth are not illuminated by the Sun. But yet, I know no man, who hath observed such things in the _Moon_; and one may be rationally a.s.sured that no _Vulcans_ are there, or that none of them burn at this time. This it is (_so he goes on_) which all Curious men, that have good _Telescopes_, ought well to attend; and I doubt not; but, if we had a very particular _Map_ of the _Moon_, as I had designed to make one with a _Topography_, as it were, of all the considerable places therein, that We or our Posterity would find some changes in Her. And if the _Mapps_ of the _Moon_ of _Hevelius_, _Divini_, and _Riccioli_ are exact, I can say, that I have seen there some places considerable enough, where _they_ put _parts that are clear_, whereas _I_ there see _dark ones_. 'Tis true that if there be _Seas_ in the _Moon_, it can hardly fall out otherwise, than it doth upon our _Earth_, where _Alluvium's_ are made in some places, and the Sea gains upon the Land in others. _I say_, if those Spots we see in the _Moon_, are Seas, as most believe them to be; whereas I have many reasons, that make me doubt, whether they be so; of which I shall speak elsewhere. And I have sometimes thought, whether it might not be, that all the Seas of the _Moon_, if there must be Seas, were on the side of the other _Hemisphere_, and that for this cause it might be that the _Moon_ turns not upon its _Axis_, as our _Earth_, {122} wherein the Lands and Seas are, as it were, ballanced: That thence also may proceed the non-appearance of any Clouds raised there, or of any Vapors considerable enough to be seen, as there are raised upon this Earth; and that this absence of Vapors is perhaps the cause, that no _Crepuscle_ is there, as it seems there is none, my selfe at least not having hitherto been able to discerne any mark thereof: For, me thinks, it is not to be doubted, but that the reputed Citizens of the _Moon_ might see our _Crepuscle_, since we see, that the same is without comparison stronger, than the _Light_ afforded us by the _Moon_, even when she is _full_; for, a little after Sun-set, when we receive no more than the _first_ Light of the _Sun_, the sky is far clearer, than it is in the fairest night of the _full Moon_. Mean while, since we see in _the Moon_, when she is increasing or decreasing, the Light she receives from the Earth, we cannot doubt, but that the People of the _Moon_ should likewise see in the _Earth_ that Light, wherewith the _Moon_ illuminates it, with perhaps the difference, there is betwixt their bigness. Much rather therefore should they see the Light of the _Crepuscle_, being, as we have said, incomparably greater. In the mean time we see not any faint Light beyond the _Section_ of the Light, which is every where almost equaly strong, and we there distinguish nothing at all, not so much that cleerest part, which is called _Aristarchus_, or _Porphyrites_, as I have often tryed; although one may there see the Light, which the _Earth_ sends thither, which is sometimes so strong, that in the _Moon's_ decrease I have often _distinctly_ seen _all_ the parts of the _Moon_, that were _not enlightned_ by the _Sun_, together with the difference of the clear parts, and the Spots, so far as to be able to discern them all. The _Shaddows_ also of all the _Cavities_ of the _Moon_ seem to be stronger, than they would be, if there were a _Second_ Light. For, although a far off, the shaddows of our Bodies, environed with Light, seem to Us almost dark; yet they doe not so appear so much, as the Shaddows of the _Moon_ doe; and those that are upon the _Edge_ of the _Section_, {123} should not appear in the like manner. But, I will determine nothing of any of these things. When I shall hereafter have made more frequent Observations of the Moon with my _great Telescopes_, in convenient time, I shall then perhaps learn more of it, than I know at present, at least it will excite the _Curious_ to endeavor to make the like Observations; and it may be, others, that I have not thought of.
_The Instance of the _same Person_ to Mr. _Hook_, for communicating his Contrivance of making, with a Gla.s.s of a Sphere of 20 or 40 foot _diameter_, a _Telescope_ drawing several hundred foot; and his offer of recompensing that Secret with another, teaching To measure with a _Telescope_ the _Distances of Objects_ upon the Earth._
In _Numb._ 4. Of these _Papers_, pag. 67. Mr. _Hook_ had intimated, that he would shortly discover a way of his, with a _Plane-convex_ Gla.s.se of a Sphaere of 20. or 40. feet _Diameter_, without _Veines_, and truly wrought of that _Figure_, to make a _Telescope_, that with a single _Eye-gla.s.s_ should draw 300, 400, yea 1000 feet, _without_ at all _altering the Convexity_: Monsieur _Auzout_ returns this consideration, and offer upon it, which follows:
To perform (_saith he_) with a _lesser Object-gla.s.s_ the effect of a _great Telescope_, we must find out a way to make such an _Object-gla.s.s_ to receive as many Rayes as one will, without their being sensibly distant from one another; to the end, that by applying to it a _stronger Eye-gla.s.s_, there may be still Beams enough to see the Object, and to obliterate the small specks and imperfections of the _Eye-gla.s.s_. And if Mr. _Hook_ hath this Invention, I esteem it one of the greatest, that can be found in the matter of _Telescopes_. If he please to impart it to us, we shall be obliged to him; and {124} I wish, I had a secret in _Opticks_ to encourage him to that communication. If I did believe, that this would be esteemed one, To measure with a _great Telescope_ the _distance of Objects_ upon the _Earth_; which I have found long since, and proposed to some by way of Paradox; _Locorum distantias ex unica statione, absque ullo Instrumento Mathematico, metiri_; I doe here promise to discover it to him, with the necessary Tables, as soon as He shall have imparted his to me; which I will use, as he shall order me. For, although the _Practise_ doe not altogether answer the _Theory_ of my Invention, because that the length of the _Telescopes_ admits of some Lat.i.tude; yet one comes near enough, and perhaps as Just, as by most of the wayes, ordinarily used with Instruments.
That, which I am proposing, I doubt not but M. _Hook_ will soon understand, and see the determination of all Cases possible. I shall only say, that if we look upon the sole _Theory_, we make use of an ordinary _Telescope_, whereof the _Eye-gla.s.s_ is to be _Convexe_: for, by putting the Gla.s.ses at a little greater distance, than they are, proportionably to the distance for which it is to serve, and by adding to it a _new Eye-gla.s.s_, the Object will be seen distinct, though obscure; and if the _Eye-gla.s.s_ be _Convexe_, the Object will appear erect. They may be done two manner of ways; either by leaving the _Telescope_ in its ordinary situation, the _Object-gla.s.s_ before the _Eye-gla.s.s_; or by inverting it, and putting _this_ before _that_. But if any will make use of two _Object-gla.s.ses_, whereof the _Focus's_ are known, the distance of them will be known. If it be supposed, that the _Focus_ of the _first_ be B. and _that_ of the _second_ C, and the distance given, B + 2D, and that D _minus_ C, be _equal_ to F; for, this distance will be _equal_ to B + C + F - rF - C. And if you have the _Focus_ of the _first Object-gla.s.s_, equal to B, the distance, where you will put the _second_ Gla.s.s equal to B + C + D, the _focus_ of the 2d Gla.s.se will be found equal to CD/{C+D}. And if you will that the Object shall be magnified as much with these two Gla.s.ses, as it would be with a single one, whereof the _Focus_ {125} should be of the distance given, having the _Focus_ of the _Object-gla.s.s_ given equal to B, and the distance to B + D; the distance between the first and the second Gla.s.s will be equal to {2B + 2BD}/{2B + D}, whence subducting B (the _Focus_ of the _Object-gla.s.s_ given) there remains BD/{2B + D}; and if this sum be supposed equal to C, we shall easily know, by the preceding Rule, the _Focus_ of the _second_ Gla.s.s.
So far M. _Auzout_, who, I trust, will receive due satisfaction to his desire, as soon as the happy end of the present Contagion shall give a beginning and life again to the Studies and Actions of our retired _Philosophers_.
I shall onely here adde, That the Secret he mentions [_Of measuring the distance of Places by a Telescope (fitted for that purpose) and from one Station_] is a thing already known (if I am not mis-informed) to some Members of our Society; who have been a good while since considering of it, and have contrived ways for the doing of it: Whether the same with those of Mr. _Auzout_, I know not. Nor have I (at the distance that I am now from them) opportunity of particular Information.
_An Experiment of a way of preparing a Liquor, that shall sink into, and colour the whole Body of _Marble_, causing a _Picture_, drawn on a surface, to appear also in the _inmost_ parts of the Stone._
This _Experiment_, having been hinted at in the next foregoing _Papers_, out of the _Mundus Subterraneus_ of _Athanasius Kircher_, and several Curious Persons, who either have not the leisure to read Voluminous Authors, or are not readily skilled in that Learned Tongue wherein the said Book is written, being very desirous to have it transferred hither, it was thought fit to comply with their desire herein.
The Author therefore of the _Mundus_, &c, having seen {126} some stones reputed to be _natural_ that had most lively Pictures, not only upon them, but pa.s.sing _thorow_ their whole substance, and thereupon finding an _Artist_; skilful to perform such rare workmans.h.i.+p, did not only p.r.o.nounce such stones to be _artificial_, but when that _Artist_ was unwilling to communicate unto him his Secret, did joyn his study and endeavors with those of one _Albertus Gunter_ a _Saxon_, to find it out themselves: wherein having succeeded, it seems, they made the Experiments which this Industrious and communicative _Jesuit_ delivers in this manner:
The Colours, saith he, are thus prepared; I take of _Aqua fortis_ and _Aqua Regis_, two ounces _ana_; of _Sal Armoniack_ one ounce; of the best _Spirit of Wine_, two drachms; as much _Gold_ as can be had for nine _Julio_'s (a _Julio_ being about six pence English) of pure _Silver_, two drachmes.
These things being provided, let the Silver, when calcined, be put into a Vial; and having powred upon it the two drachmes of _Aqua fortis_, let it evaporate, and you shall have a Water yielding first a _blew_ Colour, and afterwards a _black_. Likewise put the Gold, when calcin'd, into a Vial, and having powred the _Aqua Regis_ upon it, set it by to evaporate: then put the _Spirit of Wine_ upon the _Sal Armoniack_, leaving it also till it be evaporated; and you will have a Golden coloured Water, which will afford you divers Colours. And, after this manner, you may extract many _Tinctures_ of Colours out of other Mettals. This done, you may, by the means of these two Waters, paint what Picture you please upon white Marble, of the _softer_ kind, renewing the Figure every day for several days with some fresh superadded Liquor, and you shall find in time, that the Picture hath penetrated the _whole_ solidity of the Stone, so that cutting it into as many parts as you will, it will always represent unto you the same Figure on both sides.
_So far he_, which how far it answers expectation, is referred to the Tryal of Ingenious Artists. In the mean time there are not wanting Experienced Men that scruple the Effect, but {127} yet are far from p.r.o.nouncing any thing positively against it, so that they doe not discourage any that have conveniencies, from trying.