Page:Passages from the Life of a Philosopher.djvu/346

330 a small dot of ink upon the paper, which was moving over a table with the velocity given to it by the wheels of the carriage.

Thus the comparative frequency of these dots indicated the rate of travelling at the time. But the instrument was susceptible of giving different scales of measurement. Thus it might be that only three inches of paper passed under the pen in every mile, or any greater length of paper, up to sixty feet per mile, might be ordered to pass under the paper during an equal space. Again, the number of dots per second could, if required, be altered.

The clock was broken four or five times during the earliest experiments. This arose from its being fixed upon the platform carrying the axles of the wheels. I then contrived a kind of parallel motion, by which I was enabled to support the clock upon the carriage-springs, and yet allow it to impress its dots upon the paper, which did not require that advantage. After this, the clock was never injured.

The power of regulating the length of paper for each mile was of great importance; it enabled me to examine, almost microscopically, the junctions of the rails. When a large scale of paper was allowed, every joining was marked upon the paper.

I find, on referring to my paper records, that on the 3rd March, 1839, the "Atlas" engine drew my experimental carriage, with two other carriages attached behind it, from Maidenhead to Drayton, with its paper travelling only eleven feet for each mile of journey; whilst from Drayton to Slough, forty-four feet of paper passed under the pen during each mile of progress.

The inking pens at first gave me some trouble, but after successively discovering their various defects, and remedying