An Accompt of Sundry Experiments Made and Communicated by That Learn'd Mathematician, Dr. Erasmus Bartholin, upon a Chrystal-Like Body, Sent to Him Out of Island

PHILOSOPHICAL TRANSACTIONS. Januar. 16. 1672 The CONTENTS. An Accompt of sundry Experiments, made and communicated by that Learned Mathematician Dr. Erasm. Bartholin, upon a Crystal-like Body sent out of Island. An Extract of a Letter containing a way of making Sea water sweet. An Extract of another Letter concerning two Experiments made for finding another passage of the Urine besides the known one. A Relation of the abundance of Wood found under ground in Lincolnshire. A Description of the Stone-Quarry near Maestrich. An Accompt of some Books: I. TRACTS written by the Honourable Rob. Boyle, of a Discovery of the Admirable REFLECTION of the AIR; &c. II. ELEMENTA GEOMETRIÆ PLANÆ, Auth. Egidio Franc. de Gottignies. III. Synopsis GEOMETRICA, eum tribus opusculis, Auth. Honor. Fabri. IV. DIALOGI PHYSICI, de IUMINE; vi PERCUSSIONIS; LIQUORIS ELEVATIONE per CANALICULUM; & Variis Selectis. Auth. Hon. Fabri. V. ANTONII MOLINETII Dissertationes ANATOMICÆ & PATHOLOGICÆ de SENSIBUS & eorum Organis. An Accompt of sundry Experiments made and communicated by that Learn'd Mathematician Dr. Erasmus Bartholin, upon a Crystal-like Body, sent to him out of Island. Before we come to the Relation itself of these Experiments, we cannot but premise an Extract of the Obliging Letter, written written to the Publisher, by the said Doctor Bartholin from Copenhagen Febr. 27. 1670; English't as follows; I know the many Excellencies of the English Nation, and that innumerable new things in the matter of knowledge issue thence, and diffuse themselves through Europe; though they arrive somewhat slowly hither. We are here pressed with too many cares, that though we want no will to contribute something to the advancement of knowledge; yet being destitute of the leisure necessary for it, and diverted by two difficult Professions, the Medical and Mathematical, we can rather admire the performances of others, than engage for anything of our own. But yet, not altogether to frustrate your expectation, and to give you some Testimony of my affection and endeavors, I here send you some Experiments made with a certain Crystal-like Stone, sent me out of Island, together with a piece of that Stone, to make the Tryals yourself. Farewell. For the rest, we are now labouring to publish a more corrected and better digested Edition of Tycho Brahe's Works; a business of much time and exceeding great labour: Which care while I am engaged in, I must lay aside other matters. Yet I hope, that my part in this work will shortly be over; there remaining almost nothing, but to provide the charges necessary for the Impression; which all true Lovers of Astronomy cannot but have a great concern for. This Letter being sent to Hamborough to that Ingenious Physician, Dr. Matthias Pajenius, with a desire to transmit it to London, this worthy Person was pleased to inclose it in one of his written to the Publisher; which, since it treateth of the same argument (I mean, the Islandian Stone,) will not be amiss to subjoin here the Breviate of. The Observations of the Excellent Bartholin upon the Island-Chrystal are indeed considerable as well as painfull. We have here also made some Tryals of it upon a piece, he presented me with; which confirm his observations. Mean time, we found it somewhat scissile and reducible by a knife into thin lamina's or or plates, which, when single, shew'd the Object single, but laid upon one another, shew'd it double; the two images appearing the more distant from one another, the greater the number was of those thin plates laid on one another. With submission to better judgments, I think it to be a kind of Selenites. Some of our curious men here were of opinion, that the Rhomboid figure, proper to this Stone, was the cause of the appearances doubled thereby. But having tryed, whether in other Transparent Bodies, of the like Figure, the like would happen, we found no such thing in them; which made us suspect some peculiarity in the very Body of this Stone. These Letters being thus premised, we now come to relate the Brief of the Observations and Experiments themselves; referring the more Curious Reader to the larger Accomp of them, and their Mathematical Demonstrations, as they are to be found in the Printed Book, entitul'd Erasmi Bartholini Experimenta Chrystalli Islandici Dis-Diaclastici; quibus mira & insolita REFRACTIO detegitur. Hafniæ A. 1669. 1. The Inhabitants of Island and our own Merchants inform us, that this kind of Chrystal is found in divers places of that Country; but chiefly digg'd out of a very high mountain, not far from the Bay of Roerfjord, which lies in 65. degr. Latitude; that that Mountain reacheth Southward, and hath its whole outside made up of this substance, without a necessity of digging deep for it; that it is cut out by Iron-tooles, in bigness of a Cubick foot, or somewhat better: and that out of its corners there is sometimes found grown out a harder matter, not unfit to cut glass, of a figure different from that of the whole mass, and approaching to that of Diamonds. 2. The Figure of this Chrystal stone is like a Rhombick or Rhomboid Prisme. Nor hath the whole Body that Figure only, but all the parts of it, when broken into small pieces, keep the same; except that in some cases the ground, whence 'tis digged, yields such as are of a Triangular Pyramid-figure. 3. This Substance is Electrical, attracting (to speak with the Vulgar,) when heated, straw, Feathers, &c. 4. It is not so hard, as to endure polishing: Nor is it easily consumed; nor reduced into a calx but by a strong fire, by which it will turn into a substance like unslaked lime, which will heat a wet finger, and, when sprinkled with fountain-water, will bubble up, and become like common lime. 5. Aqua fortis being by me dropp'd upon it, it was corroded, and the superficial parts were put into a motion with some noise. And when I pulverized it in a mortar, Aqua fortis, powred on it, made it boyle, till all was dissolved, and the Attenstrum tinged with a yellowish colour. Then putting it into a Thermometer furnished with a hollow glass-ball, it considerably shew'd the difference of Heat and Cold. The powder being dissolved in Aqua fortis, I dropp'd some Spirit of Vitriol upon it, to separate the thick from the thin, and to precipitate the white calx to the bottom. 6. The sides of this Body are exceeding smooth; which is then easily obtained, if a thinner piece be nimbly broke asunder with your finger. But if you strike it with a hammer, the percussion hath not the same effect upon, nor is equally resisted from every part; whence the smooth sides of this Mineral become often scabrous. The whole Body is rather clear than bright, of the colour of limpid water; but that colour, when it hath been immersed in water, and dried again, becomes dull. Hence it is, that in its native place the upper surface is darkish; because of the Rains and Snows fallen upon it. Sometimes there appear also some reflections of colours, as in the Rain-bow. The Angles are not pointed alike, all the flat sides being obliquely inclined to one another. The opposite plains are parallel. 7. In this Chrystallin Prisme, two of the plain Angles are always acute, and the two other obtuse; and never any of them is equal to the collateral Angles of the Inclinations. 8. The Objects seen through it, appear sometimes, and in certain positions of the Prisme, double: Where 'tis to be noted, that the distance between the two images is greater or less, according to the different bigness of the Prisme; insomuch that in thinner pieces this difference of the double image almost vanisbeth. 9. The Object appearing double, both images appear with a fainter colour; and sometimes one part of the same species is obscurer than the other. 10. To an attentive Eye, one of these Images will appear higher than the other. 11. In a certain position the Image of an Object seen through this Body, appears but single, like as through any other Transparent Body. 12. We have also found a position, wherein the Object appears sixfold. 13. If any of the obtuse Angles of this Prisme be divided into two equal parts by a line, and the visual rays do pass from the Eye to the Object through that line, or its parallel, both Images will meet in that line, or in another parallel to it. 14. Whereas Objects, seen through Diaphanous Bodies, are wont to remain constantly in the same place, in what manner soever the transparent Body be moved, nor the Image on the Surface move except the Object be moved; we have observed here, that one of the Images is moveable, the other remaining fix; although there be a way also, to make the fixed image moveable, and the moveable fix in the same Crystal; and another, to make both moveable. 15. The Moveable Image doth not move at random, but always about the Fixed, which while it turneth about, it never describeth a perfect Circle but in one case. 16. Dioptricks teach, that a Diaphanous Body, having one only surface, sends from one Object but one Image refracted to the Eye; and having more Surfaces than one, it represents one Image in each; But whereas in our substance there occurs but one plain superficies to the Eye and yet a double image of one Object; it concern'd us to consider, whence this double image might be caused. Two ways offer'd themselves to us, Reflection and Refraction. How Reflection could perform it, was difficult to find. For, having dulled the clearness of the two plain sides of our Chrystallin Prisme, thereby to make them unfit for Reflecting the light; the Rays being directed through its upper and lowermost superficies, the image still still appear'd double. Again, two species appearing through a great Prisme, upon breaking of the same into pieces and to reducing it into divers smaller ones, it came to pass, that through each of these lesser portions the same object was seen always double. Whence I Collected, that if it should be said, that one of the images proceeded from the Reflection of the plain sides; the former of these Experiments would discountenance that assertion. But then if another should derive the cause from some internal Reflection of the Surfaces of this Body, certainly the same effect would not have been found in every one of its parts, but the double appearance, that was exhibited in the smallest portion, would have been multiplied in a greater bulk. Reflection therefore not satisfying, we recurred to Refraction. But, whereas 'tis known, that no image can pass through two Diaphanous Bodies of a different nature, but by Refraction, and that one image supposeth one Refraction; it did follow, that, if Refraction were made the cause of this Phenomenon, there would be a double Refraction for a double image. And, forasmuch as the Appearances of our Island-Chrysal are not of the same kind, but one of them is fixt, the other moveth, we shall also distinguish the Refractions themselves, which refract the double Rays arriving to the Eye, and call the one, which sends the Fixt image refracted to our sight, Usual; the other, which transmits the Moveable to the Eye, Unusual. And hence, namely, from this peculiar and notable propriety of the double Refraction in this Island-stone, we have not scrupled to call it Dis-diaclastic. This being supposed, it will not be irrational to suspect, that these two Refractions proceed from different principles. For, since it is commonly known from Diopticks, that an Object, by visual rays affecting the Eye, exhibits some Image on the Superficies of the Diaphanous Body, which Image is but one, as long as the Superficies is one, and the upper plain parallel to the lower; as also, that if the Eye remaining steady, the Diaphanous Body be moved, that image remains always fixt, as long as the Object, whence it comes, remains remains unmoved. Wherefore in this Transparent substance, the Image which appears fixt, may proceed according to the ordinary Laws of Usual Refraction; but that, which moveth, and is carried about according to the motion of the Diaphanous Body, while the Object remains un-stirr'd, sheweth an Unusual kind of Refraction, hitherto un-observed by Dioptricians. Hence, that I might examine the nature and difference of both, I put, upon some Object, as the point A, the Prisme of my Double refracting Chrystal N, P, R, Q, T, B, S; and the Eye M, being perpendicularly posited over the upper plain of the Prisme N, P, R, Q, I noted, whether there was any Refraction of the point A, (for the usual Laws of Refraction teach, that there is none.) But the Perpendicular 1st Ray of the Eye was observed to pass not through the Moveable but the Fixed Image; thereby being conformable to the Rules of Usual Refraction, as striking the Eye unrefracted, so that the Eye, the Image, and the Object, were seen in the same Line. But, when in the same scite of the Eye, the Object A, did also exhibit the other Image X, at no small distance from the former; I took notice, that this Object A, was not seen unrefracted by the means of the image X, though the Eye M, remain'd perpendicular over the plain; and that consequently this Unusual Refraction is not subject to the received Axiome of Dioptricks, which imports, That a Ray falling perpendicularly on the superficies of a Diaphanous Body, is not refracted, but passeth unrefracted. Next, I so placed the Eye in O, that the Ray from the Object A, arriving to the Eye, might be parallel to the lines RT and QB, of the plane R, Q, T, B, &c. then it appear'd, that the Rays were trajectioned from the Object A, without Refraction, through the Moveable image Q; the Object A, the moveable image Z, and the Eye O, being in the same line; and that the same Object A, did transmit to the Eye O, remaining in the same position, yet another species Y; through the Refracted Ray AYO Whence it was manifest to me, that this Unusual Refraction had for its Rule the Parallel of the Sides of this Double-refracting Chrystal, while the Usual Refraction was directed according to the Perpendicular of the Superficies. But considering that the place of the point, appearing through our Diaphanous Body, cannot easily be determin'd, as being only obvious in the uppermost part; we shall add the way, whereby we have found its diversity, by drawing, on the subjacent table, a straight line through that point; the place of which line will be determined by the one Eye through this Chrystal, and by the other Eye without the Chrystal. For, in the same Figure, let through the Object A, be drawn upon the Table, a strait line BC. The Eye being in M, that double line HD, and IE, will appear, the species's being cast on the upper surface: And if you attend well, you will observe observe one of the Images, viz. the Fixt H D to be congruent to the subjacent line B C, whil'st the other, namely the Moveable E I, tendeth towards R. But, if afterwards the Eye be posited in O, the same Object, I mean the line B C, will not only be represented double by the images K F, and L G; but also the Movable Image G L be congruent to the inferior line B C; while the Fixed F K is not so, but tends towards N. After the Author hath given us these Experiments, he undertaketh to determine the Quantity of the Refractions in this Double-refracting Body; and having first given the Demonstration of the Method of Measuring the Refraction of Glass, (omitted by Des-Cartes in his Dioptricks,) he finds, after several Tryals, the Angle of Inclination to the Angle of Refraction in this Island-Chrystral to be as 5 to 3. But this Ingenious Person doth not stop here, but proceeds to demonstrate all the recited Experiments; observing first, that the Teachers of the Corpuscularian Hypothesis, which includeth that of Figures and Pores, could not wish for a fitter Body, than this, to assert their Doctrine; in regard that it appears, first, that this Double-refracting Body hath its Pores according to the Ductus of the sides, and parallel therereto; since it may be observ'd, that, according to this disposition of the sides, it is broken, and the parts sever'd from one another; and that one of the Images, namely the Moveable, passeth through them. Next, besides these Pores, lying according to the Parallelisme of the sides, it hath others, such as Glass, Water, and right Chrystral have, through which the Fixt Image is transmitted. But passing by these, our Author assumeth two Hypotheses, as necessary to his design, not so much found out by Ratiocination, as by the above related Experiments. The one is, that there are some Lines, by which the Rays pass through the transparent Body un-refracted; which Lines though they have been held to be Perpendicular in Diaphanous Bodies hitherto known, yet this Author requireth not, that they should be always supposed such, since they may perhaps in some case be not such. The other is, that it may be supposed, that half the light or appearance, diffused from the Object, is refracted according to the Usual Refraction; but the other half according to the Un-usual Refraction; or, which is all one, that the Usual and Un-usual Refraction have the same power to refract the Rays of the Objects. The former of these Suppositions he collects from Exper. 14; the latter from Exp. 8. But, how he proceeds in these Deductions, and the thereon grounded Demonstrations, may be more fully and more plainly seen in the above-mentioned Treatise itself, than can be conveniently deliver'd in this Epitome. An Extract of a Letter from a Learned French Gentleman, concerning a way of making Sea-water sweet. —Monsieur Hauton hath now declared his secret of making Sea water sweet. It consists first in a Precipitation, made with Oyl of Tartar, which he knows to draw with small charges. Next, he distills the Sea-water; in which work the Furnace taketh up but little room, and is so made, that with a very little wood or coal he can distill 24 pots of water in a day: For the cooling of which, he hath this new invention, that instead of making the Worm pass through a Vessel full of water (as is the ordinary practice,) he maketh it pass through one hole, made on purpose out of the Ship, and to enter in again through another: So that the Water of the Sea performeth the cooling part: By which means he saveth the room, which the common Refrigerium would take up; as also the labour of changing the Water, when the Worm hath heated it. But then thirdly, he joyns the two precedent Operations, Filtration, thereby perfectly to correct the malignity of the Water. This Filtration is made by means of a peculiar Earth, which he mixeth and stirs with the distilled water, and at length suffers to settle at the bottom. Paris Febr. 22. 1670.