The celebrated AEolian harps of the old castle of Baden Baden are entirely different, and merit description.  One of them (Fig. 3) is formed of a resonant box, the construction of which differs from that of AEolian harps with a rectangular box, in that it is prolonged beyond the place occupied by the strings, and is rounded off behind.  In the opposite side there are two long and narrow apertures.  To prevent the apparatus from being injured by the weather, it is inclosed in a sort of case occupying the recess of the window in the old ruined castle in which it is exposed.  Behind the harp there is a wire lattice door, the purpose of which seems to be to protect the instrument against the attempts of robbers or the indiscreet contact of tourists.  We annex to the general view of the instrument a front and profile plan (Fig. 4).  The AEolian harp has often inspired both writers of prose and poetry.  Chateaubriand, in Les Natchez, compares its sounds to the magic concerts that the celestial vaults resound.  Without attributing such effects to the instrument, it must be admitted that it possesses remarkable properties, which act upon the nervous system and cause very different impressions, according to the temperament of those who listen to its accords.

[Illustration:  FIG. 4.—­PLAN OF THE BADEN BADEN INSTRUMENT.]

Hector Berlioz, in his Voyage Musicale en Italie, has given as follows the curious effects that an AEolian harp produced upon his lively and impassioned imagination:  “On one of those gloomy days that sadden the end of the year, listen, while reading Ossian, to the fantastic harmony of an AEolian harp swinging at the top of a tree deprived of verdure, and I defy you not to experience a profound feeling of sadness and of abandon, and a vague and infinite desire for another existence.”

An English physician, Dr. J.M.  Cox, in his practical Observations upon dementia, asserts that unfortunate lunatics have been seen whose sensitiveness was such that ordinary means of cure had to be given up with them, but who were instantly calmed by the sweet and varied accords of an AEolian harp.  Other observers narrate that they have heard the efficacy of Aeolian sounds spoken of in Scotland for producing sleep.

Telegraph wires are often, under the influence of the winds, submitted to vibrations which reproduce the phenomena of the Aeolian harp.  The electric telegraph, which, before the construction of the Kehl bridge, directly traversed the Rhine, very frequently resounded, and the observer who placed his ear against the poles on the bank of the river was enabled to hear something like a far-off sound of bells.—­La Nature.

* * * * *

PHYSICS WITHOUT APPARATUS.

MANUFACTURE OF ILLUMINATING GAS.

[Illustration:  FIG. 1.—­PRODUCTION OF ILLUMINATING GAS.]