What is "They Are Wont To Ascribe To Each"?

Question

Whenever men notice some similarity between two things, they are wont to ascribe to each, even in those respects in which the two differ, what they have found to be true of the other.

My Attempt

Definition of "Wont": (of a person) in the habit of doing something; accustomed.

Definition of "Ascribe":regard something as being due to (a cause).

Meaning according to me: Man is accustomed to suppose that if something is the case in first thing, then it must be the case in second thing, but then it doesn't make any sense to me.

Answer 1

A better definition of ascribe there than the one you listed, relating to causality, would be one relating to attribution generally.

To ascribe a characteristic to a thing is to state that the characteristic is an attribute of the thing.

For example.

Ice melts at room temperature.

I've ascribed the characteristic "melts at room temperature" to ice.

Ice is translucent.

Ditto, with "translucent".

Now to the gist of the sentence you quoted.

Glass is translucent.

Glass melts at room temperature.

I've (fallaciously) ascribed the attribute "melts at room temperature" to glass by virtue of its similarity to ice in respect to translucency.

P.S. The pattern of the verb can take either of these two shapes, with the meaning being the same in either case:

1. To ascribe a characteristic to something

2. To ascribe to something a characteristic.

Your sentence

Whenever men notice some similarity between two things, they are wont to ascribe to each, even in those respects in which the two differ, what they have found to be true of the other.

follows the second pattern:

...they [men] are wont to ascribe {to each [thing]} ... {what they have found to be true of the other}

what = that (characteristic) which

Answer 2

The meaning is

"People tend to assume that two things similar in one respect are similar in all respects even when that is demonstrably false."

It is making a statement about a logical fallacy to which people are psychologically prone. Your interpretation does not take into account "even in those respects in which the two [things] differ." The author does not at all agree that two things similar in one regard are necessarily similar in all. He is pointing out a common error.