Letter to Fromondus

9. On page 30: He is astonished that I recognize no other sensation than that which takes place in the brain. But all doctors and surgeons will assist me, as I hope, to persuade him; for they know that those whose limbs have been recently amputated often think they still feel pain in the parts they no longer have. And I once knew a young girl whose eyes would be blindfolded whenever the surgeon came to treat her hand injury, as she could not bear to look at it. When gangrene set into her hand, they were forced to amputate her arm up to the elbow, without informing her in order not to upset her. They skillfully attached several cloths tightly in place of what had been removed, and she remained for a long time unaware of the amputation. What is remarkable here is that she nonetheless continued to feel severe pains, sometimes in her fingers, sometimes in her metacarpus, and sometimes in her elbow which she no longer had. This was because the nerves of her hand and arm, which then terminated near the elbow and had previously extended from the brain to those parts, were moved in the same way they would have been in the extremities of her fingers or elsewhere, causing her soul to perceive similar pains. This would undoubtedly not have happened if the sensation of pain, or as he calls it, sensation, took place in the hand or elsewhere other than in the brain.

10. On pages 159 and 163: I do not understand what he objects to in my discussion of meteors. If my philosophy seems too crude to him because it considers the shapes, sizes, positions, and movements of parts as mechanics do, he condemns what I hold as most praiseworthy above all else. This approach, which I believe distinguishes me from others and of which I am most proud, is to employ a mode of philosophy in which no reason is accepted unless it is mathematical and evident, and in which conclusions are entirely supported by certain experiences. Thus, everything we conclude from these principles that can be done is indeed done whenever we apply active things to passive ones properly. I am astonished that he does not notice that this mechanicism, which has been in use until now, is nothing but a small part of true physics. Because it could not find a place among adherents of vulgar philosophy, it withdrew to mathematicians.

This part of philosophy has remained truer and less corrupted than others, as it relates entirely to usage and practice. Those who fail in it in the slightest way are usually punished by the loss of all their effort. If he despises my way of philosophizing because it resembles mechanics, it seems to me he condemns it precisely because it is true.

For we see that stones are composed of small grains, wood of small filamens; and as he himself says, the flesh is composed of small threads intertwined with each other, like the threads of a cloth; and there is nothing more conformable to reason than to hear things which, on account of their smallness, cannot be perceived by the senses, after the example and model of those we see. Let him also remember that he said himself in his objection on page 164. that the air, and the spirits enclosed in the water, raise the upper parts of the water as they come out, which cannot be stretched in Clerselier II, 43 if it does not have only this air, and these spirits are composed of several particles scattered here and there in the pores of the water.

11. Regarding water and other bodies: If he refuses to accept that water and other bodies are composed of parts distinct from one another, I urge him to observe with his eyes similar parts in many bodies. Stones are composed of small grains, wood of small filaments, and flesh of small intertwined threads like the threads of a cloth. It is most reasonable to judge things that, due to their smallness, cannot be perceived by the senses, in comparison to those we can see. Let him remember what he himself said in his objection on page 164—that air and spirits enclosed in water raise the upper parts of the water as they escape, which cannot be understood unless he admits that this air and these spirits are composed of several particles scattered here and there within the pores of the water.

If he fears that the void may break the union, which he says must necessarily exist between the parts of the universe, or if similar phantoms of subtle philosophy frighten him and prevent him from agreeing that terrestrial bodies are composed of small parts actually divided, I ask him to reread what is contained on page 164. He will see that I conceive each of these particles as a continuous body infinitely divisible, about which one could say everything he has demonstrated in his very subtle treatise on the composition of the continuum.

If, perhaps, he fears that the Venus will break the union which he says must necessarily be between the parts of the universe, and if other similar phantoms, with which subtle philosophy has been accustomed to fill its continuum, frighten him, and for this reason he will not agree that the terrestrial horns are composed of small parts now divided; I beg him to read again what is contained on page 164. and he will see that he conceives each of these particles as a continuous horn divisible to the infinity, from which we can say all that he has demonstrated in his very subtle treatise on the composition of the continuous; and he will even know that he does not expressly deny any of the things that others imagine more in the Horns, besides those which I have explained there; but nevertheless let my coarse and rustic Philosophy be content with this little thing.

11. Finally, if he convinces himself that I am recklessly and without foundation supposing that the particles of water are somewhat elongated and shaped like eels, and similar things, let him remember what is stated on page 76 of the Book of Method; and let him understand that if he is willing to take the trouble to read with sufficient attention everything I have written in the Meteors and in Dioptrics, he will find more than six hundred reasons from which one can form as many syllogisms to demonstrate the same things, in the manner that follows.

If water is more fluid, and does not freeze as easily as oil, this indicates that the latter is composed of parts that bond easily with one another, much like the branches of trees, while the former consists of more slippery components, such as those resembling eels. It has been found through experience that water is more fluid than oil, and does not freeze as readily; thus, this is evidence that oil is made up of parts that connect easily with one another, while water is comprised of more slippery elements, akin to those that take on the shape of eels.

Likewise, if it is true that linens soaked in water dry more easily than those soaked in oil, it is an indication that the parts of water have shapes akin to those of eels, which can easily exit through the pores of the fabric, whereas the parts of oil have shapes similar to those of tree branches, which tend to get more entangled in those pores; indeed, experience demonstrates that this is true; thus, etc.Similarly, if water is heavier than oil, it indicates that the parts of oil are like tree branches, which consequently leave several gaps around them, while the parts of water resemble eels, and thus they are contained within a smaller space; indeed, experience makes us aware of this; thus, etc.

In the same vein, if water evaporates more readily, or as chemists say, if it is more volatile than oil, this is a sign that water is composed of particles that, like eels, easily separate from one another, while oil is made up of particles akin to those of tree branches, which are more intertwined; this can indeed be demonstrated through experience. Thus, etc.All of these matters, when considered separately, are only probable and do not provide complete conviction, yet when viewed collectively, they possess the strength of a true demonstration. However, had I wished to present all these points in the manner of dialecticians, I certainly would have wearyed the hands of printers and fatigued the eyes of readers with the bulk of the volume.

12. On page 162. It seems to him that it is a paradox to say that a weak and slow movement causes the sensation of cold, while a strong and swift movement causes the sensation of heat. Consequently, he must also find it paradoxical that a slight friction, as mentioned by Clerselier II, 45, made on the hand causes the sensation of tingling and pleasure, while a stronger friction causes the sensation of pain. For pain and pleasure differ no less from each other than heat and cold do. He must also regard it as a paradox that if we approach a warm body with our hot hand, that body seems cold to us, although we think it is warm if we touch it with the other hand which is colder.

13. On page 164. It seems to him that it is a paradox to say that cold causes rarity. However, he does not satisfy an experiment that clearly demonstrates this. For when he states that the air and the spirits that emerge from the water condensed by cold elevate the upper parts of the water confined in a vessel; he admits that the air and the spirits exit the water, and that they elevate its upper parts, without implying that anything takes their place; thus at that moment, according to him, this water occupies more space, and altogether contains less matter than before; which undoubtedly is referred to as being rarefied by cold, and not condensed; for anyhow it may come about that a body occupies more space than it did before, it is called being rarefied. Nevertheless, one should not assume that the cause he presents for the raising of the water is true.

For if the air and the Spirits, in order to be warm, were to be driven out of the water by the force of cold, they would have to move to another place where the force of cold would be lesser; and yet, usually, there is no such place nearby, especially after the surface of the water is covered with a thick crust of ice. It should not be stated that they tend to ascend because they are light, for if the top of the vessel were completely sealed, and only the bottom remained open, that would not prevent the water that is freezing from rising.

And the reason I have given for the swelling of water is by no means undermined by the fact that ice tends to appear at the top of the vessel somewhat rarer and more porous; Clerselier II, 46 because this occurs due to the fact that the particles of water, being arranged to bend and curve in various ways, as I have stated at this point, can do so more easily towards the surface, where nothing hinders them from rising or bending, than in the middle, where they find no space to do so other than by breaking the vessel in which they are contained. Furthermore, in order to dispel any doubt that the same water, initially condensed by cold, is subsequently rarified shortly after by the same cold, one must note that in the Experiment I presented, it begins to swell while it is still completely liquid, and just before one observes the slightest particle of ice on its surface.

14. On page 165. He does not want the exhalations to be elevated by the shock and trembling of the Sun’s rays; because, he says, the Sun’s rays are not of the nature of bodies. As for me, I express it specifically, not in truth that they are bodies, but rather that they are the impulse of some bodies. This is sufficient here. And one must not deny that such an impulse occurs; because, as he says, we do not feel it: For according to the same argument, it would be necessary to say that every time we do not feel the air while walking, we walk in a vacuum. Moreover, we also feel the rays of the Sun quite distinctly through the sense of touch whenever we expose our bare skin to its rays; for they warm it, and this warmth is nothing other, as I have stated elsewhere, than a certain movement excited in the small parts of the skin by the impulse of the Sun’s rays.

But consider the little probability that exists regarding what he asserts, namely, that the fumes of exhalations and vapors are only pushed upwards due to their rarity, or by the impulse of some other heavier bodies. As if it were believable that vapors and exhalations, which are nothing more than particles of water and earth, could be elevated into the air, which is much lighter than they are, by the impulse of some other lighter bodies. Certainly, he would be right to reproach me for having never read the book of Archimedes, which discusses bodies that float on water, or at least for never having heard of it, if I had written that it contains matters that could serve to prove this.

But perhaps he will say that by these heavier bodies he means the very air, due to the fact that the Earth and Water have been truly rarefied by the force of the Sun’s rays, making them lighter than he is: As if it were at all probable, that the rays of the Sun, which never reach the water or the earth except by passing through the air, could rarefy the air so little, which is naturally very predisposed to expansion, while on the contrary rarefying the particles of these substances to such an extent that they become lighter than the air.

15. On page 182. I am astonished by his assertion that the true reason for the polished exterior surface of water, and (what he adds of his own) that it is uniformly round, should be derived from Archimedes in the same book where he discusses bodies floating on water; for nothing is contained in this book that could serve that purpose, except for this postulate, namely, that when the parts of a moist body are lying evenly, the less pressed part is displaced from its position by the one that is pressed more.

And the second proposition, in which he demonstrates, following this postulate, that the surface of any wet body which is at rest and seemingly motionless is spherical, and that the center of this sphere is the same as that of the Earth; this certainly comes quite close to the truth, and indeed as much as was necessary for Archimedes’ purpose, who had no other aim in this entire work than to demonstrate how much and in what manner ships should be loaded in order to prevent them from being submerged.

But this does not explain why the surface of the water is smooth. For contrary to this very foundation of Archimedes, and all other laws of equilibrium, if one does not take into account other circumstances, and above all this mutual friction of the surfaces that I have mentioned, it follows, as Clerselier states very clearly in II, 48, that it must be rough and uneven; because there are typically small terrestrial parts mixed among those of the water, as is manifestly evident from the fact that when kept for some time in a vase, they sink to the bottom. Furthermore, there are also some spirits within it that are lighter than it, as he himself admits in the objection on page 164.

It is demonstrated in the fourth and fifth propositions of this Book of Archimedes that those parts of the surface of the water, which have beneath them more of these small terrestrial particles and fewer spirits, must be somewhat closer to the center of the earth than the other neighboring parts that would have more spirits and fewer of these terrestrial particles, thus rendering this surface altogether rough and unrefined. Or if he wishes that the earth and spirits, and all similar things, be equal to water in weight when they are mixed with it; at least he must acknowledge that Archimedes’ reasoning is of no use unless the surface of the water or another liquid is a part of the sphere that has the center of the earth as its core. Therefore, what shall he say about water droplets that are suspended in the air and the waves of the sea, which, despite being agitated, always maintain their surfaces very equal and very smooth?

16. On pages 167 and 168, I paused for some time at this point, and I could never have imagined why he brings forth the example of the rays of a wheel and that of a circle of fire created by a lit ember when it is vigorously agitated in a circle, to refute what I have written about the rarity of vapors, if I had not recollected appropriately that Aristotle states that rarification occurs through the increase of quantity, and thus many of his followers are persuaded that a body, when rarified, occupies more space in all dimensions than when it is condensed; according to which opinion, it would be true to say that the rays of a wheel, or a burning ember agitated in a circle, are not more rare and do not occupy more space when they are in motion, Clerselier II, 49 than when they are at rest, yet my coarse philosophy does not comprehend such an increase in quantity.

And I conceive of no other rarefaction than that which occurs when the parts of a body move away from one another, causing the pores or intervals between the parts of that body to increase and become larger. And I do not claim that each of the parts of this body, whose pores are thus enlarged, becomes rarer; rather, I assert that the entire body becomes rarefied. Furthermore, I do not deny that there may be very rare bodies, even if their parts are at rest and motionless; for this is how I define a rare sponge, not only when it is dry but even more so when it is filled with water and expands further.

For it does not matter whether its pores are filled with air, water, or some other substance, as this does not pertain to its nature.

But there is nothing more evident than that a very swift movement of all parts of a body can sometimes cause all its parts to move further away from each other than if they were at rest; for example, when a burning ember is violently agitated in a circle, it prevents other embers from also being agitated in various ways in the same place; thus, he has here sought difficulty where there is none.

17. On pages 175 and 189, he denies that the flavor of salt consists in the fact that the particles of salt enter the pores of the tongue; for, he says, if this were true, whenever they happen to fall in an erratic manner, they would produce some other taste: But he must observe that a needle only pricks with its point, and that a sword only cuts with its edge, and cannot make any incision with its other parts; and similarly, the small particles of salt that fall irregularly on the tongue are not felt any more than those of fresh water; but because there is an infinite number of such particles in a single grain, it is just as impossible that one of these grains, upon dissolving in the mouth, sends any of its particles into the pores of the tongue as it is for a person to walk barefoot on thorns without getting hurt.

He adds that it is in vain that I hope to disentangle myself from such a great number of difficulties through mere location and motion, which cannot be understood or explained without several other real qualities. However, if he is willing to take the trouble to enumerate the problems I have explained in the sole Treatise on Meteors, and to compare them with what has been written by others on the same subject, in which he is very well versed, I hope he will not find much reason to despise my philosophy, as crude and mechanical as it may be.

18. Finally, on page 190. When he states that all the varieties that arise from the movement of the Winds cannot be entirely explained by the mere example of the Eolipiles, he agrees with me; for I also present other causes. However, when he asserts that the exhalations of the winds are not so tightly compressed between the clouds and the mountains, that they escape from them and are expelled with as much force as the vapor that emerges from an Eolipile, he seems not to pay enough attention to the laws of Mechanics, by which it can be easily demonstrated that if this large mass of air, which constitutes the winds, were pushed with as much force as is customary for the small amount of air that escapes from an Eolipile, there would be no buildings that would not be overturned and brought to the ground.

Here, Sir, is what came to my mind in the Spirit to address the objections of Monsieur Fromondus; that if this does not entirely satisfy him, or if perhaps after a more thorough examination of my Book, he finds several other objections to raise against me, etc.