Fig. 4.
In these experiments my assistant, Mr. Cottrell, has rendered me material assistance.[93]
Note, June 3d.—I annex here a sketch of an apparatus[94] devised by my assistant, Mr. Cottrell, and constructed by Tisley and Spiller, for the demonstration of the law of reflection of sound. It consists of two tubes (A F, B R) with a source of sound at the end R of one of them, and a sensitive flame at the end F of the other. The axes of the tube converge upon the mirror, M, and they are capable of being placed so as to inclose any required angle. The angles of incidence and reflection are read off on the graduated semicircle. The mirror M is also movable round a vertical axis.
FOOTNOTES:
[1] It will be borne in mind that the Washington Appendix was published nearly a year after my Report to the Trinity House.
[2] That is to say, homogeneous air with an opposing wind is frequently more favorable to sound than non-homogeneous air with a favoring wind. We had the same experience at the South Foreland.—J. T.
[3] Had this observation been published, it could only have given me pleasure to refer to it in my recent writings. It is a striking confirmation of my observations on the Mer de Glace in 1859.
[4] Had I been aware of its existence I might have used the language of General Duane to express my views on the point here adverted to. See Chap. VII., pp. [340]-341.
[5] This does not seem more surprising than the passage of light, or radiant heat, through rock salt.