TO H. R. DROOP, Esq.

                                                                  Glenlair, Dalbeattie, 19th July 1865.

     There are so many different forms in which Societies may be cast, that I should like very much to hear something   of what those who have been thinking about it propose as the plan of it.

     There is the association for publishing each other's productions; for delivering lectures for the good of the public  and the support of the Society; for keeping a reading room or club, frequented by men of a particular turn; for  dining together once a month, etc.

     I suppose W—— 's object is to increase the happiness of men in London who cultivate physical sciences, by their      meeting together to read papers and discuss them, the publication of these papers being only one, and not the   chief end of the Society, which fulfils its main purpose in the act of meeting and enjoying itself. 

     The Royal Society of Edinburgh used to be a very sociable body, but it had several advantages. Most of the   fellows lived within a mile of the Society's rooms. They did not need to disturb their dinner arrangements in order  to attend.

     Many of them were good speakers as well as sensible men, whose mode of considering a subject was worth  hearing, even if not correct.

     The subjects were not limited to mathematics and physics, but included geology, physiology, and occasionally   antiquities and even literary subjects. Biography of deceased fellows is still a subject of papers. Now those who cultivate the mathematical and physical sciences are sometimes unable to discuss a paper, because they would  require to keep it some days by them to form an opinion on it, and physical men can get up a much better   discussion about armour plates or the theory of glaciers than about the conduction of heat or capillary attraction.

The only man I know who can make everything the subject of discussion is Dr. Tyndall. Secure his attendance and  that of somebody to differ from him, and you are all right for a meeting.

     If we can take the field with a plan in our head, I dare say we could find a good many men who would   co-operate.

     We ride every day, sometimes both morning and evening, and so we consume the roads. I have made 68   problems, all stiff ones, not counting riders.

I am now getting the general equations for the motion of a gas considered as an assemblage of molecules flying  about with great velocity. I find they must repel as inverse fifth power of distance.