The peculiar property possessed by various materials/which has received the general name of elasticity, exhibits itself in many ways. Some substances manifest it, when compressed, in high degree, while bars of the same material may be bent without developing elastic power to any great extent. Others On the Contrary, exhibit great elastic power when bent, and Comparatively little upon compression. Others, again, may be stretched without manifesting much elasticity, while upon bending they show it in a high degree. Springs may be classed as follows : Flat, straight, or bar springs, coiled springs, spiral springs, and block springs, intended to resist compression, usually made of rubber, and in common use on railroad cars, etc.,convex disks, concave disks, or a union of the two latter in a corrugated spring. In metallic springs it is found that the elastic power resides in great measure near the surface. A well-tempered bar Spring will lose much of its elastic strength by filing off a very thin scale from its surface. This fact has never yet been explained satisfactorily. Power may be applied to springs in four ways. They may be stretched, compressed, bent, or twisted. The elasticities developed in the same material by these different methods of application, are not demonstrated to possess any ratio to each other. In fact, the mathematical data relating to springs are extremely meager, and it is greatly to be desired that some accurate experimenter would give to the world some tabulated results that could be relied upon with certainty as a guide in construction. At the present time there is nothing of this kind, so far as we know, that can be referred to. It is evident from the fact above stated namely, that the elastic power of springs lies, in a great part, near or upon their surfaces that the form of the metal which presents the greatest surface will give the maximum power, within certain undetermined limits. The doubling of the thickness, the width remaining constant, will not give double power, while doubling the width will nearly double the elastic power if the thickness be the same. But while the elastic force is found to be in some way dependent upon the surface, it is also evident that there must be some ratio which the thickness should possess in regard to the other proportions, in order that the maximum effects should be maintained. It is easy to see that were the leaves of an ordinary elliptical carriage spring much reduced in thickness their strength would be impaired. At present the determination of the strength of springs is left almost wholly to experiment. It is plain also, that whatever data may be determined for springs having proportional dimensions, and considered as being formed of homogeneous material, and of the same temper, nothing but experiment could determine their strength with accuracy, for, although dimensions may be accurately determined, the quality of the metal and exactness of temper can never be relied upon as constant. Approximate results, however, might be obtained of great use in the construction of this important element of machinery. The uses of springs seem constantly multiplying. A large number of most important machines, such as printing presses, and the like, employ them in almost all their forms. In many clocks, and all watches, they are the prime movers, while their employment for all sorts of vehicles need not be more than alluded to. A class of rather visionary inventors have vainly (as yet) endeavored to use them as the propelling power for vehicles, and we receive many communications requesting our views upon the feasibility of so doing. While there is theoretically no impossibility, in the idea of such propulsion, we think we can see so many practical difficulties in the way of its accomplishment as to render its success extremely doubtful. These practical difficulties are so well known that they need not here be specified. Mechanical skill may possibly eventually overcome them, but let not the mistake be made that a spring possesses any more power than is delegated to it. It is only a magazine of power, and can give only what it has previously received. We should have considered this last remark unnecessary had it not been that the tone of some communications lately received indicates that their authors have not-fully purged themselves of the old illusion of the perpetual motion.