CURVE OF PROGRESS REGISTERED. 333
self-acting machinery governing points impinging upon the paper on which the velocity is marked.
Whenever any unusual resistance has opposed the progress of the train, it will thus be marked upon the paper. It will indicate in some measure the state of the road, and it will assuredly furnish valuable information in case an accident happens, and the train or the engine gets off the rails.
The third recommendation I have to make is —
That ihe curve described hythecerUre of the engine itself upon the plane of the railway should he laid doum upon the paper.
Finding this a very important element, I caused a plate of hardened steel to be pressed by a strong spring against the inner edge of the rail. It was supported by a hinge upon a strong piece of timber descending from the platform supporting the carriage itself. The motion of this piece of steel, arising from the varying position of the wheels themselves upon the rail, was conveyed to a pen which transferred to the paper the curve traversed by the centre of the carriage referred to the plane of the rail itself.
The contrivance and management of this portion of my apparatus was certainly the most difficult part of my task, and probably the most dangerous. I had several friendly cautions^ but I knew the danger, and having examined its various causes, adopted means of counteracting its effect.
After a few trials we found out how to manage it, and although it often broke four or five times in the course of the day's work, the fracture inevitably occurred at the place intended for it^ and my first notice of the fact often arose from the blow the fragment made when suddenly drawn by a strong rope up to the imder side of the floor of our experimental carriage.
I have a very strong opinion that the adoption of such