An improvement in the construction of car wheels and trucks, for turning curves upon railroads, has been invented by John T. Den-niston, of Lyons, ?. ?. It is well known to our'readers that a multiplicity of devices have been brought before the public for obviating the difficulties encountered in turning curves; many of these inventions have been very good ones, although but few of them have ever been thoroughly tested in practical use. A device was described in the Scientific American a few weeks since, in which, by a very ingenious contrivance the axles of the cars were made to assume the form ot radii to the curve. Many other contrivances have been used, some of which were very good and others ot no practical utility. The one invented by Mr. Deniston has certainly one thing to recom mendit, and this is simplicity ; in his improvement the object is accomplished by making the rim of the wheel somewhat thicker then is used, and forming the flange in the centre of this rim, thus forming two treads, one upon each side of the flange. The circumference of the tread upon the inside of the flange being larger than that upon the outside. When the curwe is turned, this inner tread takes a new rail, placed near the outer rail of the curve, and thus causes the cars naturally to run in a circular direction. It will be observed that the outer wheel, in turning curves thus instantly, becomes larger than the inner wheel, which gives the curvilinear motion. The inventor has taken measures to secure a patent.