In answer to your enquiry, I may state the result of my personal experience and observation thus :-1. Alcoholic liquors, when taken in such quantity as to excite the circulation, are unfavourable to all inquiries requiring care and accuracy, but not unfavourable to efforts of the imagination. 2. Tobacco taken in small quantities is not unwholesome in its action on mind or body. When taken in excess it is not easy to define or describe its action, the chief fact relating to it being that it increases the number of the pulse, but lessens the force of the heart. 3. My personal experience of such quantities of wine as two or more glasses of port a day at my age (72) is that it produces no perceptible or measurable effect when taken for, say, three weeks or a month at a time, when compared with the like period of total abstinence. 4. It may be said in favour of temperance or even of extreme abstinence, that some of those men who have done most work in their day--John Howard, Wesley, and Cobbett, for example--have been either very moderate, or decidedly abstemious. But on the other hand, such men as Samuel Johnson, who was a free liver and glutton, and Thackeray, who drank to excess, have also got through a great amount of work. WILLIAM A. GUY. Feb. 25, 1882. PROFESSOR ERNST HAECKEL, JENA. I find strong coffee very useful in mental work. Of alcohol, I take very little, because I find it of no value as a stimulant. I have never smoked. E. HAECKEL. November 4, 1882. MR. PHILIP GILBERT HAMERTON.