I am interested in the fact that anyone is engaged in a thorough investigation of the action of stimulants. Although the subject falls under my own studies in some degree, I am a very indifferent testimony as far as concerns personal experience. On the action of tobacco, I am disqualified to speak, from never having used it. As to the other stimulants--alcohol and the tea group--I find abstinence essential to intellectual effort. They induce a false excitement, not compatible with severe application to problems of difficulty. They come in well enough at the end of the day as soothing, or cheering, and also as diverting the thoughts into other channels. In my early intercourse with my friend; Dr. Carpenter, when he was a strict teetotaler, he used to discredit the effect of alcohol in soothing the excitement of prolonged intellectual work. I have always considered, however, that there is something in it. Excess of tea I have good reason to deprecate; I take it only once a day. The difficulty that presses upon me on the whole subject is this:--In organic influences, you are not at liberty to lay down the law of concomitant variations without exception, or to affirm that what is bad in large quantities, is simply less bad when the quantity is small. There may be proportions not only innocuous, but beneficial; reasoning from the analogy of the action of many drugs which present the greatest opposition of effect in different quantities. I mean this--not with reference to the inutility for intellectual stimulation, in which I have a pretty clear opinion as regards myself--but as to the harmlessness in the long run, of the employment of stimulants for solace and pleasure when kept to what we call moderation. A friend of mine heard Thackeray say that he got some of his best thoughts when driving home from dining out, with his skin full of wine. That a man might get chance suggestions by the nervous excitement, I have no doubt; I speak of the serious work of composition. John Stuart Mill never used tobacco; I believe he had always a moderate quantity of wine to dinner. He frequently made the remark that he believed the giving up of wine would be apt to be followed by taking more food than was necessary, merely for the sake of stimulation. Assuming the use of stimulants after work to aid the subsidence of the brain, I can quite conceive that tobacco may operate in this way, as often averred; but I should have supposed that any single stimulant would be enough: as tobacco for those abstaining entirely from alcohol, and using little tea or coffee. ALEXANDER BAIN. March 6, 1882. PROFESSOR ROBERT S. BALL, LL. D., F. R. S., ANDREWS PROFESSOR OF ASTRONOMY IN THE UNIVERSITY OF DUBLIN, AND ROYAL ASTRONOMER OF IRELAND.