We are conservatives in • respect to inventions which are old and useful, and reformers in respect to those which are old and of an inferior character. Plain common sense teaches any man that it is foolishness itself to prefer an invention merely because it is new, and deride another merely because it is old. We are also advocates of all that is new and useful, but it requires experience, a great amount of knowledge, and disinterested judgment to tell what is new and useful; whether it has been employed before and superseded by something better, or had been before proposed, experimented with and failed, or has inherent defects. It frequently happens that old and exploded inventions are revived and presented to the public with the most glowing eulogies of their superiority and incomparable qualities ; and it no less' frequently happens that others possessing inherent defects are as prominently paraded and more vauntingly advocated. It is our duty—and we have often to perform it—to expose the worthlessness of the one class and the errors of the other. This we do without any reference to private and invidious prejudices—for we have none of them—but as public journalists speaking the truth as we believe it. We believe that much wrong is prevented from being perpetrated on 1Ihe public by timely exposures ot unworthy objects, many of which it has fallen to our lot to hold up', either to scorn (according to the manner in which they were heralded) or to a candid and kind criticism. Almost daily, we have either old or inferior inventions presented to us for our opinion, by honest and worthy inventors, many of whom are disappointed at discovering the age or inferiority of their plans, but generally all satisfied with our conclusions. Two years ago we were asked for our opinion about propelling a ferry boat across a river in South Carolina by the power of a huge spring wound up with a cranI!:; we informed the inventor that the same device had been applied to a boat in this city in 1808, and that it had inherent defects. * Nothing but a trial, however, would satisfy the inventor, and that did satisfy him to his cost, but he thanked us for our information. Three years ago a gentleman in Syracuse, N. Y., asked our opinion about a substitute for the crank which he had invented ; we gave our opinion that there was no loss by the crank, and it was the most simple and best device ever invented to convert rectilinear into rotary motion.— The inventor concluded he would try his own device; the result of his experiments, however, confirmed every word we had said, and his testimony to this effect we published on page 99, Vol. 5. We could name a great many such cases, but we have not room to do so. Of the many public exposures which we have mad'e, not one, we believe, has turned out different from what we predicted, although we are liable to make mistakes as well as others, for none are perfect, but we are disinterested. In our last volume we gave our opinion respecting the worthlessness of a project which was presented to the public in this city for navigating plank and common roads with steam carriages. It would have been easy to have proven us incorrect if we were wrong, by the said company putting their plans in operation; and when we consider that this could have been done at no very great outlay, and that the company was composed of editors, lawyers, artists, 'c., who make pretensions to science, and practical mechanics, it is certainly presumptive evidence that some of them have become convinced that we were right, if not, they have acted unwisely. It is now eighteen years since Robert Mills, engineer and architect in Washington, published a pamphlet recommending the adoption of steam carriages for common roads. At that time, (1834) railroads were almost unknown in our country; there was but a single short railroad then in this State, (N. Y.) Since . then railroads have multiplied until they have laced our entire country with an iron network of 12,000 miles. To advocate steam carriages on common roads now, when we on which the resistance is twenty times less, betrays a great want of judgment. With respect to new and superior modes of travelling; too much attention cannot be bestowed upon them. The steamboat and railroad are fast revolutionizing the world ; but it is not to be supposed that we are yet at the end of such inventions and improvements. A means of safely, cheaply, and rapidly navigating the atmosphere may yet be invented, but no plan hitherto proposed or tried meets these positively necessary conditions; we confess, however, that we have far more confidence in balloons than steam carriages on common roads. An invention to be successful must not only be new, but useful—an improvement. Any plan or invention having these qualities, no matter by whom invented or proposed, we advocate with pleasure and hail with delight.