There appears to be a great mania for self- acting brakes, worked by the momentum 0f the cars, &c., and I beg to give all those gentlemen of the Brake Party a little advice; that is—they will never succeed in their plans as at present directed; for the moment you attach a complicated apparatus to railroad machinery, you are destined to fail ; besides, the sudden coalition and rebounding of a train of cars will not produce power sufficient to be of any effect, without the introduction ot yet more complicated machinery ' that will condemn itself at once. The best self-acting brake is a sober trustworthy man, with powerful but common and simple double brakes; let railroad companies pay for good men in all their departments—practical men 0f common sense—and you will not hear of those terrible accidents any more. But as long as railroads and steamboats are controlled by men with more tongue than brains, and more brass than knowledge, these accid e«ts will continue t0 occur. As for the self- acting brake, I helped to apply the same principle several years ago, but finding no benefit derived from it, Ilet the matter drop; m fact, to obtain leverage enough, the car must have- an action, or space b,'tween eac h, 0f atleast two or three feet, which woald cause a continual oscillation, or jerking, as the couplings came into action or otherwise, and of course would cause most dangerous spaces between the platform, to say nothing of a disagreeable motion t the passengers,—as cars, to ride easy, should be firmly and closely attached to each other and to the engine, so as to render them, comparatively, one solid body, allowing no room tor jerks; —then, and not till then, will passengers be freed from those disagreeable bumps or jerks when the train starts or stops. Yours, &c., JoHlt J. Jones, Supt. of A.R. R.