MESSRS. EDITORS—In the Scientific American of the 13th inst., I find a description of White's Patent Equalizing or Self-adjusting Truck, and as you state that to you it appears to be a good improvement, and one that will conduce greatly to the safety of railroad travelling, I wish to point out what, in my opinion, is an obiectionable feature of the invention, and which might lead to throwing the locomotive off the track, instead of tending to keep it on,—1 allude to the eccentric cup or movable centre, which, if it required to be moved much to make the driving wheels track, would cause the truck to run to one side, and consequently tend to mount the rail, thereby causing the result it is meant to avbid. I call it anything but a scientific remedy for the driving wheels not tracking. There is but one correct position for the centre-plate or saddle, and that is exactly in the centre-line of the engrne,and .so in the centre-line of the truck, the position fore and aft may be varied with safety, as it frequently is by placing the centre-plate forward the centre of the truck, thus giving the controlling influence to the hind wheels of the truck, but it is not safe to move it sideways. Being a railroad man I take pleasure in improvements conducing to the safety of engineers and the travelling community. With respect to carrying the weight on the centre of the truck, it is a good but not a new plan, as I will proceed to show :—solTe tenor more years ago, I cannot state the time exactly, I built a locomotive, which was then named the ' Owasco,' which was put upon the Buffalo and Attica Railroad, and has been in use ever since, and is now on the Buffalo al'd Rochester Railroad; this locomotive has a centre- cup plate, of cast-iron, chilled, and the centre- pin or saddle which is attached to the boiler ia also of cast-iron chilled on the end, the truck carrying the weight on the centre, and the cup bearing allowing the truck to accommodate itself to inequalities in the road, and as tar as I can learn, it has never broken a spring either upon the truck or driving wheels, and is said to be the best engine on the road for keeping the track. I do not claim to be the inventor, as I believe the invention was made by Eastwick&Harrison, formerly of Philadelphia, P'l. Yours, &c., W. S. Hudson. Paterson, N. J.. Nov. 6, 1852. L We are happy to receive communications from practical men, upon all subjects, and in order to benefit all classes we are pleased to insert their communications, whether as criticisms on inventions or as suggestions to their improvements, providing they are penned in a proper style and dictated by correct motives. — [ed.