To Thomas Jefferson May, 1788
To Thomas Jefferson May, 1788
Your saying last evening that Sir Isaac Newton's principle of gravitation would not explain, or could not apply as a rule to find the quantity of the attraction of cohesion and my replying that I never could comprehend any meaning in the term "attraction of cohesion," the result must be that either I have a dull comprehension, or that the term does not admit of comprehension. It appears to me an jumble of words-each of which admits of a clear and distinct idea, but of no idea at all when compounded.
The immense difference there is between the attracting power of two Bodies. At the least possible difference the mind is capable of conceiving, and the great power that instantly takes place to resist separation when the two Bodies are incorporated prove, to me, that there is something else to be considered in the case than can be comprehended by attraction or gravitation.1 Yet this matter appears sufficiently luminous to me according to my own line of ideas.
Attraction is to matter what desire is to the mind but cohesion is an entire different thing produced by an entire different cause. It is the effect of the figure of matter.
Take two iron hooks, the one strongly magnetical and bring them to touch each other, and a very little force will separate them-for they are held together only by attraction.
But their figure renders them capable of holding each other infinitely more powerful to resist separation than what attraction can; by hooking the
Now if we suppose the particles of matter to have figure capable of interlocking and embracing each other we shall have a clear distinct idea between cohesion and attraction and that they are things totally distinct from each other and arise from as different causes.
The welding of two pieces of iron appears to me no other then entangling the particles in much the same manner as turning a key within the works of a lock, and if our eyes were good enough we should see how it was done.2
I recollect a scene at one of the Theatres that very well explain the difference between attraction and cohesion. A condemned Lady wished to see her child and the child its mother. This call attraction. They were admitted to meet, but when ordered to part they threw their arms round each other and fastened their persons together. This is what I mean by cohesion-which is a mechanical contact of the figures of their persons as I believe all cohesion is.
Though the term "attraction of cohesion" has always appeared to me like the Athanasion creed3, yet I think I can help the philosopher to a better explanation of it than what they give themselves-which is, to suppose the attraction to continue in such a direction as to produce the mechanical interlocking of the figure of the particles of the bodies attracted.
Then suppose a male and female screw lying on a table and attracting each other with a force capable of drawing them together. The direction of the attracting power to be a right line till screws begin to touch each other and then if the direction of the attracting power to be circular the screws will be screwed together. But even in this explanation, the cohesion is mechanical, and the attraction serves only to produce the contact.
While I consider attraction is a quality of matter capable of acting at a distance from the visible presence of matter, I have as clear an idea of it as I can have of invisible things. And while I consider cohesion is the mechanical interlocking of particles of matter, I can conceive the possibility of it much easier than I can attraction, because I can by crooking my fingers see figures that will interlock. But no visible figure can explain attraction, therefore to endeavor to explain the less difficulty by the greater appears to me unphilosophical. The cohesion which others attribute to attraction and which they cannot explain, I attribute to figures which I can explain.
A number of fish hooks attracting and moving towards each other will show me there is such a thing as attraction. But their figurative hooking together shows cohesion visibly, and a handful of fish hooks threw together in a heap explain cohesion better than all the Newtonian philosophy. It is with gravitation as it is with all new discoveries; it is applied to explain too many things4.
It is a rainy morning and I am waiting for Mr. Parker, and in the meantime, having nothing else to do I have amused myself with writing this.