There is scarcely a week passes that we have not presented for inspection some startling theory, founded upon an improper conception of a principle in science, which, according to the sanguine expectations of the inventor, is in its practical operation to produce a revolution in the particular branch of mechanics or social life to which it refers. At one time an enthusiastic inventor ignores the well-known law in mechanics that the raising of a given weight of any material requires the expenditure of a corresponding amount of power, and attempts to create a power by raising water by the aid of an Archimedean screw to supply a water wheel, or some equally fallacious process. At another, we have a plan for almost doubling the power of a high-pressure steam engine, by simply passing the exhaust steam through an auxiliary re-acting rotary engine ; the author not reflecting that in the precise proportion as the steam in its escape from a steam cylinder is impeded, will there be a re-acting force exerted against the piston. Indeeed, many of the systems and alleged improvements brought to our notice, and applauded by editors of newspapers who should know feetter, are founded on more vain hypothesis than those we have mentioned. Oftentimes they are the result of the thoughts of men of otherwise really eminent abilities, who are guided by the purest intentions. It is to these latter that we wish to offer a few remarks. When you conceive a design having for its object the production of an extraordinary result—such, for instance, as increasing the speed of machinery without a corresponding increase of power, subject it to a scientific scrutiny and judgment, lest when your ardor has persuaded you beyond the bounds of sober judgment, and caused you to subject to practical test what well-known principles had already declared impracticable, you will be regarded rather as an enthusiast than as a man of science. If a man, having the reputation of experience and knowledge in any branch of the arts, in the glow of his ambition and enthusiasm, endeavors to destroy all distinctions, and to erect a fine-spun but fallacious system on the ruin of a more perfect mode], he inflicts a downright injury upon what is conceded as sound. Many persons, in examining their plans and reasoning, will find that by endeavoring to accomplish what is unattainable, they prejudice the mind against what is practicable. And though it may be said that such speculations have their use, as they afford hints of improvement, yet, in view of the character of their authors, they are attended with this dangerous inconvenience, that the mind in search after truth is discouraged in its progress when it finds those whom it has been led to regard as its most capable conductors deviating into the mazy tracks of luxuriant fancy, instead of leading it through the safer paths of sound philosophy and practical science.