Chapter 3

_The forty ninth_ Experiment, _Of making Lakes_ (369.) _A particular example in Turmerick_ (370, 371.) Annotation _the first, That in Precipitations wherein Allum is a Coefficient, a great part of them may consist of the Stony particles of that Compound Body_ (from 372 to 375.) Annotation _the second, That Lakes may be made of other Substances, as Madder, Rue,_ &c. _but that Alcalizate Salts do not Always Extract the same Colour of which the Vegetable appears_ (from 376 to 378.) Annotation _the third, That the_ Experiments _related may Hint divers others_ (378) Annotation _the fourth, That Alum is usefull for the preparing other than Vegetable Pigments_ (379.)

_The fiftieth_ Experiment, _Of the Similar effects of_ Saccarum Saturni _and_ Alkalies, _of Precipitating with Oyl of_ Vitriol _out of_ Aqua-fortis, _and Spirit of_ Vinegar; _and of divers Varyings of the Colours, with these Compounded_ (from 380 to 384.) _Another very pretty_ Experiment, _with a Solution of_ Minium (384, 385.) _That these_ Experiments _Skilfully digested may hint divers matters about Colours_ (386.) _The Authors Apologetick conclusion, in which is Cursorily hinted the Bow or Scarlet Dye_ (387.) _The Authors Letter to Sir_ Robert Moray, _concerning his Observations on the Shining Diamond_ (391. &c.) _And the Observations themselves_.

* * * * *

Errata.

Pag. 142. l. 20. These words, _And to manifest_, with the rest of what is by a mistake further printed in this fourth Experiment, belongeth, and is to be referred to the end of the second Eperiment, p.137. pag. 145. l. 1. leg. _matter_. 146. l. 4. leg. _Bolts-head_. pag 161. in the marginal note l. 2. dele _de_ ib. l. 3. lege lib 1. p 163. l. ult. insert _where_ between the words _places_ and _the_. p. 164 l. 1. dele _that_. ibid, l. 8. leg _Epidermis_. ibid. l. 19 leg. 300. for 200. p. 169. l. 22. leg. _into it_. p. 170. l. 23. & 24. leg. _Some Solutions hereafter to be mentioned_, for _the Solutions of Potashes_, and other _Lixiviate Salts_. p. 171. l. 6. insert _part of_ between the words _most_ and _dissolved_ p. 176. l. ult. insert the participle _it_ between the words _Judged_ and _not_ p. 234. l. 4. leg. _Woud-wax_ or _Wood-wax_. p. 320 l. 29. leg. _urine_ for _urne_.

* * * * *

_THE_ _EXPERIMENTAL HISTORY_ _OF COLOURS BEGUN._

THE FIRST PART.

CHAP. I.

1 I have seen you so passionately addicted, _Pyrophilus_ to the delightful Art of Limning and Painting, that I cannot but think my self obliged to acquaint you with some of those things that have occurred to mee concerning the changes of Colours. And I may expect that I shall as well serve the _Virtuosi_ in general, as gratifie you in particular, by furnishing a person, who, I hope, will both improve my Communications, and communicate his Improvements, with such Experiments and Observations as may both invite you to enquire seriously into the Nature of Colours, and assist you in the Investigation of it. This being the principal scope of the following Tract, I should do that which might prevent my own design, if I should here attempt to deliver you an accurate and particular Theory of Colours; for that were to present you with what I desire to receive from you; and, as farr as in mee lay, to make that study needless, to which I would engage you.

2 Wherefore my present work shall be but to divert and recreate, as well as excite you by the delivery of matters of fact, such as you may for the most part try with much _ease_, and possibly not without some _delight_: And lest you should expect any thing of Elaborate or Methodical in what you will meet with here, I must confess to you before-hand, that the seasons I was wont to chuse to devise and try Experiments about Colours, were those daies, wherein having taken Physick, and finding my self as unfit to speculate, as unwilling to be altogether idle, I chose this diversion, as a kind of Mean betwixt the one and the other. And I have the less scrupled to set down the following Experiments, as some of them came to my mind, and as the Notes wherein I had set down the rest, occurr'd to my hands, that by declining a Methodical way of delivering them, I might leave you and my self the greater liberty and convenience to add to them, and transpose them as shall appear expedient.

3 Yea, that you may not think mee too reserv'd, or look upon an Enquiry made up of meer Narratives, as somewhat jejune, am content to _premise_ a few considerations, that now offer themselves to my thoughts, which relate in a more general way, either to the Nature of Colours, or to the study of it. And I shall _insert_ an _Essay_, as well Speculative as Historical, of the Nature of Whiteness and Blackness, that you may have a _Specimen_ of the History of Colours, I have sometimes had thoughts of; and if you dislike not the Method I have made use of, I hope, you, and some of the _Virtuosi_, your friends, may be thereby invited to go thorow with _Red, Blew, Yellow_, and the rest of the particular Colours, as I have done with _White_ and _Black_, but with farr more sagacity and success. And if I can invite Ingenious men to undertake such Tasks, I doubt not but the Curious will quickly obtain a better Account of Colours, than as yet we have, since in our Method the Theorical part of the Enquiry being attended, and as it were interwoven with the Historical, whatever becomes of the disputable Conjectures, the Philosophy of Colours will be promoted by the indisputable Experiments.

* * * * *

CHAP. II.

1 To come then in the first place to our more general Considerations, I shall begin with saying something as to the Importance of examining the Colours of Bodies. For there are some, especially _Chymists_, who think, that a considerable diversity of Colours does constantly argue an equal diversity of Nature, in the Bodies wherein it is conspicuous; but I confess I am not altogether of their mind; for not to mention changeable Taffaties, the blew and golden necks of Pidgeons, and divers Water-fowl, Rainbows Natural and Artificial, and other Bodies, whose Colours the Philosophers have been pleased to call not Real, but Apparent and Phantastical; not to insist on these, I say, (for fear of needlesly engaging in a Controversie) we see in Parrots, Goldfinches, and divers other Birds, not only that the contiguous feathers which are probably as near in properties as place, are some of them Red, and others White, some of them Blew, & others Yellow, _&c._ but that in the several parts of the self-same feather there may often be seen the greatest disparity of Colours; and so in the leaves of Tulips, July-flowers, and some other Vegetables the several leaves, and even the several parts of the same leaf, although no difference have been observed in their other properties, are frequently found painted with very different Colours. And such a variety we have much more admired in that lovely plant which is commonly, and not unjustly call'd the _Marvayl of Peru_; for of divers scores of fine Flowers, which in its season that gaudy Plant does almost daily produce, I have scarce taken notice of any two that were dyed perfectly alike. But though _Pyro_: such things as these, among others, keep mee from daring to affirm, that the Diversity and change of Colours does _alwaies_ argue any great difference or alteration, betwixt, or in, the Bodies, wherein it is to be discerned, yet that _oftentimes_ the Alteration of Colours does signifie considerable Alterations in the disposition of parts of Bodies, may appear in the Extraction of Tinctures, and divers other Chymical Operations, wherein the change of Colours is the chief, and sometimes the only thing, by which the Artist regulates his proceeding, and is taught to know when 'tis seasonable for him to leave off. Instances of this sort are more obvious in divers sorts of fruits, as Cherries, Plums, &c. wherein, according as the Vegetable sap is sweetned, or otherwise ripened, by passing from one degree to another of Maturation, the external part of the fruit passes likewise from one to another Colour. But one of the noblest Instances I have met with of this kind, is not so obvious; and that is the way of tempering Steel to make Gravers, Drills, Springs, and other Mechanical Instruments, which we have divers times both made Artificers practise in our presence, and tryed our selves, after the following manner, First, the slender Steel to be tempered is to be hardened by heating as much of it as is requisite among glowing Coals, till it be glowing hot, but it must not be quenched assoon as it is taken from the fire (for that would make it too brittle, and spoil it) but must be held over a bason of water, till it descend from a White heat to a Red one, which assoon as ever you perceive, you must immediately quench as much as you desire to harden in the cold water. The Steel thus hardened, will, if it be good, look somewhat White and must be made bright at the end, that its change of Colours may be there conspicuous; and then holding it so in the flame of a Candle, that the bright end may be, for about half an inch, or more, out of the flame, that the smoak do not stain or sully the brightness of it, you shall after a while see that clean end, which is almost contiguous to the flame, pass very nimbly from one Colour to another, as from a brighter Yellow, to a deeper and reddish Yellow, which Artificers call a _sanguine_, and from that to a fainter first, and then a a deeper Blew. And to bring home this Experiment to our present purpose, it is found by daily Experience, that each of these succeeding Colours argue such a change made in the texture of the Steel, that if it be taken from the flame, and immediately quenched in the tallow (whereby it is setled in whatever temper it had before) when it is Yellow, it is of such a hardness as makes it fit for Gravers Drills, and such like tools; but if it be kept a few minutes longer in the flame till it grow Blew, it becomes much softer, and unfit to make Gravers for Metalls, but fit to make Springs for Watches, and such like Instruments, which are therefore commonly of that Colour; and if the Steel be kept in the flame, after that this deep Blew hath disclosed it self, it will grow so soft, as to need to be new hardened again, before it can be brought to a temper, fit for Drills or Penknives. And I confess _Pyro._ I have taken much pleasure to see the Colours run along from the parts of the Steel contiguous to the flame, to the end of the Instrument, and succeed one another so fast, that if a man be not vigilant, to thrust the Steel into the tallow at the very nick of time, at which it has attain'd its due Colour, he shall miss of giving his tool the right temper. But because the flame of a Candle is offensive to my weak eyes, and because it is apt to either black or sully the contiguous part of the Steel which is held in it, and thereby hinder the change of Colours from being so long and clearly discern'd, I have sometimes made this Experiment by laying the Steel to be tempered upon a heated bar of Iron, which we finde also to be employ'd by some Artificers in the tempering of such great Instruments, as are too big to be soon heated sufficiently by the flame of a Candle. And you may easily satisfie your self _Pyro_: of the differing hardness and toughness, which is ascribed to Steel temper'd at different Colours, if you break but some slender wires of Steel so temper'd, and observe how they differ in brittleness, and if with a file you also make tryal of their various degrees of hardness.

2 But _Pyrophilus_, I must not at present any further prosecute the Consideration of the importance of Experiments about Colours, not only because you will in the following papers finde some instances, that would here be presented you out of their due place, of the use that may be made of such Experiments, in discovering in divers bodies, what kind the salt is, that is predominant in them; but also because a speculative Naturalist might justly enough allege, that as Light is so pleasing an object, as to be well worth our looking on, though it discover'd to us nothing but its self; so modifi'd Light called Colour, were worth our contemplation, though by understanding its Nature we should be taught nothing else. And however, I need not make either you or my self excuses for entertaining you on the subject I am now about to treat of, since the pleasure _Pyro_: takes in mixing and laying on of Colours, will I presume keep him, and will (I am sure) keep mee from thinking it troublesome to set down, especially after the tedious processes (about other matters) wherewith I fear I may have tyr'd him, some easie, and not unpleasant Experiments relating to that subject.

3 But, before we descend to the more particular considerations, we are to present you concerning Colours, I presume it will be seasonable to propose at the very entrance a Distinction; the ignorance or neglect of which, seems to mee to have frequently enough occasioned either mistakes or confusion in the Writings of divers Modern Philosophers; for Colour may be considered, either as it is a quality residing in the body that is said to be coloured, or to modifie the light after such or such a manner; or else as the Light it self, which so modifi'd, strikes upon the organ of sight, and so causes that Sensation which we call Colour; and that this latter may be look'd upon as the more proper, though not the usual acception of the word Colour, will be made probable by divers passages in the insuing part of our discourse; and indeed it is the Light it self, which after a certain manner, either mingled with shades, or some other waies troubled, strikes our eyes, that does more immediately produce that motion in the organ, upon whose account men say they see such or such a Colour in the object; yet, because there is in the body that is said to be coloured, a certain disposition of the superficial particles, whereby it sends the Light reflected, or refracted, to our eyes thus and thus alter'd, and not otherwise, it may also in some sense be said, that Colour depends upon the visible body; and therefore we shall not be against that way of speaking of Colours that is most used among the Modern Naturalists, provided we be allowed to have recourse when occasion shall require to the premis'd distinction, and to take the more immediate cause of Colour to be the modifi'd Light it self, as it affects the Sensory; though the disposition also of the colour'd body, as that modifies the Light, may be call'd by that name Metonimically (to borrow a School term) or Efficiently, that is in regard of its turning the Light, that rebounds from it, or passes thorow it, into this or that particular Colour.

4 I know not whether I may not on this occasion add, that Colour is so far from being an Inherent quality of the object in the sense that is wont to be declar'd by the Schools, or even in the sense of some Modern Atomists, that, if we consider the matter more attentively, we shall see cause to suspect, if not to conclude, that though Light do more immediately affect the organ of sight, than do the bodies that send it thither, yet Light it self produces the sensation of a Colour, but as it produces such a determinate kind of local motion in some part of the brain; which, though it happen most commonly from the motion whereinto the slender strings of the _Retina_ are put, by the appulse of Light, yet if the like motion happen to be produc'd by any other cause, wherein the Light concurrs not at all, a man shall think he sees the same Colour. For proof of this, I might put you in mind, that 'tis usual for dreaming men to think they see the Images that appear to them in their sleep, adorn'd some with this, and some with that lively Colour, whilst yet, both the curtains of their bed, and those of their eyes are close drawn. And I might add the confidence with which distracted persons do oftentimes, when they are awake, think, they see black fiends in places, where there is no black object in sight without them. But I will rather observe, that not only when a man receives a great stroak upon his eye, or a very great one upon some other part of his head, he is wont to see, as it were, flashes of lightning, and little vivid, but vanishing flames, though perhaps his eyes be shut: But the like apparitions may happen, when the motion proceeds not from something without, but from something within the body, provided the unwonted fumes that wander up and down in the head, or the propagated concussion of any internal part in the body, do cause about the inward extremities of the Optick Nerve, such a motion as is wont to be there produc'd, when the stroak of the Light upon the _Retina_ makes us conclude, that we see either Light, or such and such a Colour: This the most ingenious _Des Cartes_ hath very well observ'd, but because he seems not to have exemplifi'd it by any unobvious or peculiar observation, I shall indeavour to illustrate this doctrine by a few Instances.

5 And first, I remember, that having, through Gods goodness, been free for several years, from troublesome Coughs, being afterwards, by an accident, suddenly cast into a violent one, I did often, when I was awaked in the night by my distempers, observe, that upon coughing strongly, it would seem to mee, that I saw very vivid, but immediately disappearing flames, which I took particular notice of, because of the conjecture I am now mentioning.

6 An excellent and very discreet person, very near ally'd both to you and mee, was relating to mee, that some time since, whilst she was talking with some other Ladies, upon a sudden, all the objects, she looked upon, appeared to her dyed with unusual Colours, some of one kind, and some of another, but all so bright and vivid, that she should have been as much delighted, as surpriz'd with them, but that finding the apparition to continue, she fear'd it portended some very great alteration as to her health: As indeed the day after she was assaulted with such violence by Hysterical and Hypocondrical Distempers, as both made her rave for some daies, and gave her, during that time, a Bastard Palsey.

7 Being a while since in a Town, where the Plague had made great havock, and inquiring of an ingenious man, that was so bold, as without much scruple to visit those that were sick of it, about the odd symptomes of a Disease that had swept away so many there; he told mee, among other things, that he was able to tell divers Patients, to whom he was called, before they took their beds, or had any evident symptomes of the Plague, that they were indeed infected upon peculiar observations, that being asked, they would tell him that the neighbouring objects, and particularly his cloths, appear'd to them beautifi'd with most glorious Colours, like those of the Rainbow, oftentimes succeeding one another; and this he affirm'd to be one of the most usual, as well as the most early symptomes, by which this odd Pestilence disclos'd it self: And when I asked how long the Patients were wont to be thus affected, he answered, that it was most commonly for about a day; and when I further inquired whether or no Vomits, which in that Pestilence were usually given, did not remove this symptome (For some used the taking of a Vomit, when they came ashore, to cure themselves of the obstinate and troublesome giddiness caus'd by the motion of the ship) reply'd, that generally, upon the evacuation made by the Vomit, that strange apparition of Colours ceased, though the other symptomes were not so soon abated, yet he added (to take notice of that upon the by, because the observation may perchance do good) that an excellent Physician, in whose company he was wont to visit the sick, did give to almost all those to whom he was called, in the beginning before Nature was much weakened, a pretty odd Vomit consisting of eight or ten dramms of Infusion of _Crocus Metallorum_, and about half a dramm, or much more, of White Vitriol, with such success, that scarce one of ten to whom it was seasonably administred, miscarried.

8 But to return to the consideration of Colours: As an apparition of them may be produced by motions from within, without the assistance of an outward object, so I have observed, that 'tis sometimes possible that the Colour that would otherwise be produced by an outward object, may be chang'd by some motion, or new texture already produced in the Sensory, as long as that unusual motion, or new disposition lasts; for I have divers times try'd, that after I have through a Telescope look'd upon the Sun, though thorow a thick, red, or blew glass, to make its splendor supportable to the eye, the impression upon the _Retina_, would be not only so vivid, but so permanent, that if afterwards I turned my eye towards a flame, it would appear to mee of a Colour very differing from its usual one. And if I did divers times successively shut and open the same eye, I should see the adventitious Colour, (if I may so call it) changed or impair'd by degrees, till at length (for this unusual motion of the eye would not presently cease) the flame would appear to mee, of the same hew that it did to other beholders; a not unlike effect I found by looking upon the Moon, when she was near full, thorow an excellent Telescope, without colour'd Glass to screen my eye with; But that which I desire may be taken notice of, because we may elsewhere have occasion to reflect upon it, and because it seems not agreeable to what Anatomists and Optical Writers deliver, touching the relation of the two eyes to each other, is this circumstance, that though my Right eye, with which I looked thorow the Telescope, were thus affected by the over-strong impression of the light, yet when the flame of a Candle, or some other bright object appear'd to me of a very unusual Colour, whilst look'd upon with the Discompos'd Eye, or (though not so notably) with both eyes at once; yet if I shut that Eye, and looked upon the same object with the other, it would appear with no other than its usual Colour, though if I again opened, and made use of the Dazled eye, the vivid adventitious Colour would again appear. And on this occasion I must not pretermit an Observation which may perswade us, that an over-vehement stroak upon the Sensory, especially if it be naturally of a weak constitution, may make a more lasting impression than one would imagine, which impression may in some cases, as it were, mingle with, and vitiate the action of vivid objects for a long time after.