Letter from Erasmus Darwin to James Watt, 1767/08/18
Darwin writes to Watt about his ideas for improving carriages and commenting on Watt’s developing theories for steam engines.
Lichfield Augt. 18-67
I have been so continually engaged in travelling about the Country from sick People to sick People, that it was not till this Afternoon in my Power to measure the Iron-work of my Chaise.
There is an iron Crank in this Shape, and the Arm of the Axle is on the same Crank, and stands out at (W).
Perhaps it would be better at the angle (a)? But in this Place it admits of the Wheels being larger in the act of Turning. a b is 13 In. / a w 1½ Inch / a c 12 In / a b is square 1½ Inch / a c is round. The Pearch is a Cross.
Mr Edgeworth has put the arm of the Axle at the angle a in one He shew’d to the Society of Arts, and the Duke of York has a Phaeton made after it. The two fore-Wheels are 4 ft high.
My Cart is to draw a Ton, by Two Horses, a-breast. The wheels are seven feet Hight. The Body swings under the Axis. Now I think the Body should be fix’d to the Axis, and the Arms of the Axis should be cylindrical, and not the frustrum of a Cone. And 3rd the Axis should, as near as may be, pass through the Center of the Load. 4th the Horses should be link’d to the Body of the Cart, to avoid the additional Weight of the Frame in which my Cart-Body swings. By these means a very slight Pole alone is necessary which may rest on the Back of either of the Horses; and they may back as mine do, by pressing against the Swingle-tree Bar, and have a broad leather behind in the Harness, that their naked Shins may not come against the Woodwork. NB I have not well digested this!
This is my Cart as elegant as I can draw it, the Pole is suspended by a Strick across the Backs of the two Horses.
Enough of Carts and Chaises! – now my dear new Friend, I first hope you are well, and less hypochondriacal; and that Mrs Watt and your Child are well. The Plan of your Steam-Improvements I have religiously kept secret, but begin myself [to?] see some difficulties in the Execution that did not strike me when you was here.
I have got another and another new Hobby-Horse since I saw you. I wish the Lord would send you to pass a week with me, and Mrs Watt along with you, – a Week! – a Month, a Year.
You promised to send me an Instrument to draw Landscapes with. – If you ever move your Place of Residence for any long time from Glasgow, pray acquaint me. – I hope you have heard from Anthony Tissington. – Adieu.