TRANSACTIONS OF THE SECTIONS. 23 
twelfth part. The first volume of the ‘Annales de Chimie’ (1816) contains a 
paper by M. Delaroche, giving the results of some experiments made on this sub- 
ject. It appeared from the experiments,—first, that at small distances the wind 
has hardly any perceptible effect, the sound being propagated almost equally well in 
a direction contrary to the wind and in the direction of the wind; secondly, that 
the disparity between the intensity of the sound propagated in these two directions 
becomes proportionally greater and greater as the distance increases; thirdly, that 
sound is propagated rather better in a direction perpendicular to the wind than even 
in the direction of the wind. The explanation offered by the author of the present 
communication is as follows. If we imagine the whole mass of air in the neigh- 
bourhood of the source of disturbance divided into horizontal strata, these strata do 
not all move with the same velocity. The lower strata are retarded by friction 
against the earth, and by the various obstacles they meet with ; the upper by friction 
against the lower, andsoon. Hence the velocity increases from the ground upwards, 
conformably with observation. This difference of velocity disturbs the spherical 
form of the sound-wave, tending to make it somewhat of the form of an ellipsoid, 
the section of which by a vertical diametral plane parallel to the direction of the 
wind is an ellipse meeting the ground at an obtuse angle on the side towards which 
the wind is blowing, and an acute angle on the opposite side. Now, sound tends 
to propagate itself in a direction perpendicular to the sound-wave ; and if a portion 
of the wave is intercepted by an obstacle of large size, the space behind is left in a 
sort of sound-shadow, and the only sound there heard is what diverges from the 
general wave after passing the obstacle. Hence, near the earth, in a direction con- 
trary to the wind, the sound continually tends to be propagated upwards, and con- 
sequently there is a continual tendency for an observer in that direetion to be left in 
a sort of sound-shadow. Hence, at a sufficient distance, the sound ought to be 
‘very much enfeebled ; but near the source of disturbance this cause has not yet had 
time to operate, and therefore the wind produces no sensible effect, except what 
arises from the augmentation in the radius of the sound-wave, and this is too small 
fo be perceptible. In the contrary direction, that is, in the direction towards 
which the wind is blowing, the sound tends to propagate itself downwards, and to 
be reflected from the surface of the earth; and both the direct and reflected waves 
contribute to the effect perceived. The two waves assist each other so much the 
better, as the angle between them is less, and this angle vanishes in a direction per- 
pendicular to the wind. Hence, in the latter direction the sound ought to be pro- 
pagated a little better than even in the direction of the wind, which agrees with the 
experiments of M. Delaroche. Thus the effect is referred to two known causes,— 
the increased velocity of the air in ascending, and the diffraction of sound. 
ASTRONOMY. 
On the Distribution of the Orbits of the Comets in Space. 
By Cavaliere O. F. Mosorttt. 
The author not being present, this communication was read and explained by 
Prof. Bolzani. The author commenced by explaining that the simplest and most 
direct method of analysing the distribution of the comets in space would seem to be, 
to divide the celestial sphere by means of so many circles parallel to the ecliptic into 
equal zones corresponding to an aliquot part of the entire superficies, and then to 
ascertain how many culminating points are contained in each of these. If the orbits 
were uniformly distributed throughout space, each of them should contain about an 
equal number of these points; if not, the greater or less number contained in each 
will serve to show the tendency the orbits have to approach to or recede from that 
distribution. The author applied this method arithmetically in the first instance ; 
and afterwards, in order to render the results more palpable, reduced them to a 
graphic construction. The learned Professor then exhibited and explained to the 
Section, in detail, the several formule on which the numerical examination of the 
question was founded, and then exhibited and explained the graphic construction 
