The author then proceeds to give a description of a very delicate instrument, and various apparatus for measuring the propagation and intensity of sound, and the various experiments both in the dark, and in day-light, and likewise under different changes of the atmosphere, which were made with his apparatus--all of which tended to prove that light had a sensible influence in the propagation of sound. But the detail of these experiments and their several results would be too tedious to be here transcribed.--The night has generally been considered as more favourable than the day for the transmission of sound. ‘That this is the case (says Parolette) with respect to our ears cannot be doubted; but this argues nothing against my opinion. We hear further by night on account of the silence, and this always contributes to it, while the noise of a wind favourable to the propagation of a sound, may prevent the sound from being heard.’ In reference to the cause which produces the effect now stated, he proposes the following queries. ‘Is the atmospheric air more dense on the appearance of light than in darkness? Is this greater density of the air or of the elastic fluid that is subservient to the propagation of sound, the effect of aeriform substances kept in this state through the medium of light?’ He is disposed, on the whole, to conclude, that the effect in question is owing to the action of light upon the oxygen of the atmosphere, since oxygen gas is found by experiment to be best adapted to the transmission of sound. Our author concludes his communication with the following remarks:--‘Light has a velocity 900,000 times as rapid as that of sound. Whether it emanate from the sun and reach to our earth, or act by means of vibrations agitating the particles of a fluid of a peculiar nature--the particles of this fluid must be extremely light, elastic and active. Nor does it appear to me unreasonable, to ascribe to the mechanical action of these particles set in motion by the sun, the effects its presence occasions in the vibrations that proceed from sonorous bodies. The more deeply we investigate the theory of light, the more we must perceive, that the powers by which the universe is moved reside in the imperceptible particles of bodies; and that the grand results of nature are but an assemblage of an order of actions that take place in its infinitely small parts; consequently, we cannot institute a series of experiments more interesting than those which tend to develope the properties of light. Our organs of sense are so immediately connected with the fluid that enlightens us, that the notion of having acquired an idea of the mode of action of this fluid presents itself to our minds, as the hope of a striking advance in the knowledge of what composes the organic mechanism of our life, and of that of beings which closely follow the rank assigned to the human species.’ * * * * *