|Written from 18 Duke Street, London. The letter promises to send Piazzi Smyth an example of the spinning toy that has sparked Brunel's ideas about Smyth's instrument stand and offers suggestions about improving the toy and asks Smyth's opinions about the physical and mechanical principles underlying the toy's operation. The letter mentions that Brunel has ordered a similar, albeit improved, instrument and comments on what Brunel considers the likely outcome of alterations or improvements in the design. Brunel also discusses the way various writers use children's toys to explain physical forces or effects and describes the design for a mechanical instrument based on some of these principles and asks for Smyth's advice on understanding some of the principles of the design he has developed. There are illustrative sketches of Brunel's ideas on Folios 354 and 356.