To James Croll   14th. Jan. 1865

The Athenaeum | 14^th. Jan. 1865

My dear Sir

It is both amusing and interesting to me to trace the parallelism which has run between your thoughts & mine on the subject of “negative fluorescence.” (I have changed this term to Calorescence) The very experiment to which you refer,¹ of rendering a body hot by concussion is the one which most influenced my conviction that it was possible to produce incandescence by invisible rays.

It strikes me you are rather hard on the phrase “breaking up long periods into short ones.” In the case of the hammer there is a conversion of the mechanical motion into molecular motion, and in the case of the hydrogen flame there seems to me to be a conversion of the long periods into short ones. The fact at all events is that you hit the mass with waves of slow recurrence, and that you obtain, in return from the mass, waves of quick recurrence.

Excuse this hurried scrawl. Do you wish me to send your note to the Philosophical Magazine?² If so I would suggest one small & unimportant alteration. Instead of saying “an abuse of language” I would say an incorrect use of language.

Yours very truly | John Tyndall

Wellcome, MS. 7777/08