Letter, from Sir John Herschel to Marc Seguin Autograph letter signed by sender. Thanks for Marc Seguin's works, communicated through [Picot] Tremblay. Worries that John Frederick William Herschel has insufficient time and lags behind in the physical sciences. Comments on ideas put forward in 1824 by John Frederick William Herschel and discussed by Marc Seguin. Has found Marc Seguin's name connected with suspension bridge over Rhone River. 1861-7 or later