Item 223 - Letter from Peter Barlow

Woolwich - The experiments on the Liverpool line were made at PB's request - 'or rather I should call them observations. I requested simply to be informed of the exact speeds up and down the several planes on the Liverpool line as observed in ordinary journeys with the amount of load, the boiler pressure &c'. However, although PB does not doubt that the observations were carefully made, he finds them very irregular. PB thinks the pressure of the atmosphere on the piston has been hitherto neglected: 'we ought to consider the whole pressure in the bodies and to consider this as opposed not only to the resistance of the load, but to the pressure of the atmosphere which must be overcome with the velocity of the piston - this makes an immense difference on the computed affects'.