From Arthur Trevelyan   15 Dec. 54.

Tyneholm Pencaitland.¹ | 15 Dec. 54.

Dear Sir

Pray accept my thanks for the copy of your memoir; on the Vibration of substances at different temperatures,² when in contact – which I have perused with much gratification – and I may mention, that during my experiments I obtained vibrations in several instances, when assisting as you appear to have done, by ‘shaking the rocker’ but not considering such as fair experiments, I only note those as successful in which the vibration took place spontaneously – after the heated bar had been placed in the steadiest manner possible on its seat – or otherwise to insure spontaneity the vibrating temperature was raised by placing a lighted spirit lamp – beneath the end of the Bar over-hanging its seat, on which it had been previously placed when cold, and not afterwards touched during the exp^t.

The Balancing-bar I contrived for the purpose for enabling the vibration without the tone – to be seen by parties readily in a lecture-room at too great a distance *, to observe the movements in the vibrating-bar itself – and the longitudinal groove in the bar was only made during some of my earliest expts. as I soon found out its inutility.

Also thank you for the notice of mi theories.

Yours faithfully | Arthur Trevelyan

Dr. John Tyndall | Royal Institution | London

* from the Expts.

RI MS JT/1/TYP/5/1775

LT Typescript Only