194 
Scientific Intelligence. 
manner of producing them is attended with the peculiar advan- 
tage, that an instrument so constructed can never go out of tune 
in the smallest degree.’’ 
5. Voice changed hy breathing Hydrogen . — Mr Cooper has 
found, that if a person speaks immediately after breathing hy- 
drogen gas, for a few moments his voice suffers a change, which 
soon goes off — of Science^ No. xvii. p. 182. 
6. Humboldt on the Increase of Sound during the Night. 
1 1 has been remarked, even by the ancients, that the intensity 
of sound is greatly increased during the night. Humboldt was 
particularly struck with this fact when he heard the noise of 
the great cataracts of the Orinoco in the plain which surrounds 
the Mission of the Apures. This noise is three times greater 
in the night than in the day. Some writers have ascribed this 
to the cessation of the humming of insects, the singing of bmds, 
and the action of the wind upon the leaves of trees ; but this 
cannot be the cause of it at the Orinoco, where the humming of 
insects is much greater in the night than in the day, and where 
the breeze is never felt till after sunset. Humboldt therefore as- 
cribes it to the presence of the sun, which acts on the propaga- 
tion and intensity of sound, by opposing them with currents of 
air of different density, and partial undulations of the atmo- 
sphere, caused by the unequal heating of different parts of the 
ground. In these cases, the waves of sound are divided into 
two waves, where the density of the medium suddenly changes, 
and a sort of acoustic mirage is produced, arising from the want 
of homogeneity of the air, in the same manner as the luminous 
mirage is produced from an analogous cause. — Ann, de Chim. 
tom. xiii. p. 162. 
7. New Musical InstrumenU’-^Nl. Schortman of Buttstead 
has invented a new musical keyed instrument, the tones of which 
are produced by short rods of burned wood, of various lengths 
and breadths, thrown into a state of vibration by a current of air. 
Its pianissimo resembles the Eolian harp, and it is described as 
imitating the harmonica, clarionet, horn, hautboy, and violin. 
8. Method of 'playing on the Violin and the Violincelh at 
the same time , — Mr James Watson, a blind musician from Dun- 
dee, has invented a method by which he can play upon these two 
