"The labouring man, in the present age, if he does but read, has more helps to London: PUBLISHED BY M. SALMON, MECHANICS' MAGAZINE OFFICE, 115, FLEET STREET. M.DCCC.XXX. 739 F PREFACE ΤΟ THE TWELFTH VOLUME. ALEXANDER THE GREAT is said to have wept because he had no more worlds to conquer. A greater than Alexander -the immortal Newton-though he achieved more than all the conquerors that ever lived, yet sighed to think he had but picked up a few pebbles on the great shore of truth. The melancholy of the Macedonian hero, is happily such as can never have a place in the breasts of those, who look only to have leisure when they have no more to learn. In philosophy there are always new worlds to conquer. A limit there will ever be, beyond which the longest sword cannot reach a period to all glory reaped in fields of blood: but as has been well observed by another illustrious philosopher (over whose early grave the Genius of Discovery yet bends and weeps)," SCIENCE is like that nature of which it treats; it is neither limited to time nor space; and the more we know, the more we feel how much remains to be known."* When we reflect that our vocation is cast in a sphere thus boundless and inexhaustible, we feel that it would be to boast of little, were we to speak of the Volumes we have numbered, or of the abundance and variety of the matters which they contain. The " MECHANICS' MAGAZINE" is but now entering its teens: while other journals, devoted to similar objects, have had their years of jubilee to celebrate; and some bid fair even to rival the green old age of our learned and much respected friend, “Sylvanus Urban, Gent.” But though we may not claim any consideration on the score of either arduous or long service-though we must allow it to be easy to gather, where we have but to stretch forth the sickle and reap, and hard to tire where novelty awaits us at every step-we shall have all the encouragement we desire, if it be only granted, that we have increased in usefulness as we have increased in years, and kept advancing in the estimation of our readers, as we have added Volumes to our series. * Discourses of Sir Humphrey Davy. Discourse IV. The period over which the present Volume of our journal extends, has been distinguished by occurrences which illustrate remarkably, the propriety of that diffidence of the extent of human knowledge, which those who have penetrated deepest into the mysteries of nature, have always been the readiest to avow. We allude in a special manner to the recent experiments with locomotive-carriages on the Liverpool and Manchester Railway, and to the new and important facts in science which they have been the means of developing. Most writers on locomotion-as well those who have drawn their conclusions from practical observation, as those who have built their faith on theoretical calculation-have treated the notion of travelling on railways by steam, or any other power, at the rate of twelve or fifteen miles an hour, as perfectly chimerical: but the experiments in question have, for the first time, placed beyond all doubt, that at least double that speed is attainable with perfect ease and safety. The chief source of the incredulity which has prevailed on this head, has been the existence of very erroneous ideas with respect to the retarding effects of friction, which the same experiments have clearly shown to have been hitherto much exaggerated. It has been calculated by some that friction operates as a resistance to motion on a level railway in the ratio of 12 lbs. per ton; by others, that it bears only the ratio of 10 lbs.: but these experiments have established, that by the use of wheels of an improved construction, the friction may be actually reduced to as low as 2 lbs. per ton. Again: though it was generally allowed that steamcarriages might be propelled on a level railway at a considerable velocity, without the help of rack-rails or any other contrivance to prevent the slipping of the wheels, it was as generally maintained that they could not be employed with much useful effect on inclined planes of a greater inclination than 1 in 200; that on a plane of 1 in 96, they would just be able to move their own weight; and that when the ascent reached 1 in 60, they would come to a stand still. Now, it has been farther shown by the experiments to which we refer, that up a plane, such as that on which it was supposed a steam-carriage could just move itself, it can draw with ease three times its own weight, at the rate of, at least, ten miles an hour; or to put the case more popularly, that instead of a feather-weight it can carry fifteen tons, at the rate of ten miles an hour, or a carriage with thirty persons at the rate of |