As I am otherwise engaged, I take this opportunity of provoking you to write a letter or two. I have begun to write    Elastic Equilibrium, and I find that I must write you a letter in order at least, indeed, to serve on the one     hand as an excuse to myself for sticking up, and on the other hand as a sluice for all the nonsense which I would     have written. I therefore propose to divide this letter as follows:—My say naturally breaks up into—1. Education;   2. Notions; 3. Hearsay.

1. Education—Public.

10-11.—Gregory is on Alloys of Metals just now. Last Saturday I was examined, and asked how I would do if   the contents of a stomach were submitted to me to detect arsenic, and I had to go through the whole of the   preparatory processes of chopping up the tripes, boiling with potash, filtering, boiling with H C L and K O C L  O5, all which Kemp the Practical says are useless and detrimental processes, invented by chemists who want   something to do. 11-12.—Prof. Forbes is on Sound and Light day about as Bob well knows, and can tell you if
he chooses. He (R. C.) has written an essay [128] on Probabilities, with very grand props in it; everything original,    but no signs of reading, I guess. It was all written in a week. He has despaired of Optics.
12-1. Wilson, after    having fully explained his own opinions, has proceeded to those of other great men: Plato, Aristotle, Stoics,    Epicureans. He shows that Plato's proof of the immortality of the soul, from its immateriality, if it be a proof,    proves its pre-existence, the immortality of beasts and vegetables, and why not transmigration? (Do you   remember how Raphael tells Adam about meats and drinks in Paradise Lost?) (Greek Iambics, if you please.)
He quarrels with Aristotle's doctrine of the Golden Mean,—"a virtue is the mean between two vices,"—not   properly understanding the saying. He chooses to consider it as a pocket rule to find virtue, which it is not meant  to be, but an apophthegm or maxim, or dark saying, signifying that as a hill falls away on both sides of the top, so    a virtue at its maximum declines by excess or defect (not of virtue but) of some variable quantity at the disposal of    the will. Thus, let it be a virtue to give alms with your own money, then it is a greater virtue to pay one's debts to
the full. Now, a man has so much money: the more alms he gives up to a certain point, the more virtue. As soon as   it becomes impossible to pay debts, the virtue of solvency decreases faster than that of almsgiving increases, so    that the giving of money to the poor becomes a vice, so that the variable is the sum given away, by excess or   defect of which virtue diminishes, say I; so that Wilson garbles Aristotle,—but I bamboozle myself. I say that    some things are virtues, others are virtuous or generally lead to virtue. Substitute goods for virtues, and it will be
more general: thus, Wisdom, Happiness, Virtue, are goods, and cannot be in excess; but Knowledge, Pleasure,    and—what? (please tell me, Is it Propriety, Obedience, or what is it?) lead to the other three, and are not so much    goods as tending to good; whereas particular knowledges, pleasures, and obediences may be in excess and lead    to evils. I postpone the rest of my observations to my Collection of the Metaphysical principles of Moral  Philosophy founded on  the three laws of Liberty, Equality, Fraternity, thus expressed :—

1. That which can be done is that which has been done; that is, that the possibility (with respect to the agent) of an  action (as simple) depends on the agent having had the sensation of having done it.

2. That which ought to be done is that which (under the given conditions) produces, implies, or tends to the  greatest amount of good (an excess or defect in the variables will lessen the good and make evil).

3. Moral actions can be judged of only by the principle of exchange; that is , our own actions must be judged  by the laws we have made for others; others must be judged by putting ourselves in their place.

22d March.

At Practical Mechanics I have been turning Devils of sorts. For private studies I have been reading Young's   Lectures, Willis's Principles of Mechanism, Moseley's Engineering and Mechcanics, Dixon on Heat, and   Moigno's Répertoire d'Optique. This last is a very complete analysis of all that has been done in the optical way   from Fresnel to the end of 1849, and there is another volume a-coming which will complete the work. There is in  it besides common optics all about the other things which accompany light, as heat, chemical action, photographic rays, action on vegetables, etc.

My notions are rather few, as I do not entertain them just now. I have a notion for the torsion of wires and rods,   not to be made till the vacation; of experiments on the action of compression on glass, jelly, etc., numerically done   up; of papers for the Physico-Mathematical Society (which is to revive in earnest next session!); on the relations of   optical and mechanical constants, their desirableness, etc., and suspension-bridges, and catenaries, and elastic   curves. Alex. Campbell, Agnew, and I are appointed to read up the subject [130] of periodical shooting stars,   and to prepare a list of the phenomena to be observed on the 9th August and 13th November. The Society's  barometer is to be taken up Arthur's Seat at the end of the session, when Forbes goes up, and All students are   invited to attend, so that the existence of the Society may be recognised.

I have notions of reading, the whole of Corpus Juris and Pandects in no time at all; but these are getting   somewhat dim, as the Cambridge scheme has been howked up from its repose in the regions of abortions, and is as far forward as an inspection of the Cambridge Calendar and a communication with Cantabs.

Mr. Bob is choosing his college. I rejected for him all but Peter's, Caius, or Trinity Hall, the last being, though  legal, not in favour, or lazy, or something. Caius is populous, and is society to itself. Peter's is select, and knows   the University. Please give me some notions on these things, both for Bob and me. I postpone my answer to you   about the Gorham business till another time, when also I shall have read Waterland on Regenration, which is with   Mrs. Morrieson, and some Pusey books I know. In the meantime I admire the Judgement as a composition of great art and ingenuity.

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