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HISTOBY OF PHYSICAL ASTEONOMY.

During the total eclipse of 1842, it was universally remarked that thecolours of terrestrial objects were changed.

M. D’Hombres-Firmas perceived that when three-fourths of the sunwere eclipsed, objects of a reddish colour, and the human countenanceespecially, appeared paler, and acquired an olive hue. According to M.Lordat, a few minutes before the commencement of the totality of theeclipse, objects appeared to have a slight tinge of yellow; the light anonbecame wan and livid; in certain positions the human countenance hada cadaverous aspect * * * § .

Sig. Piola states that the observers of the eclipse in Italy generallyremarked that towards the total obscuration objects assumed a greenishtinge, which passed gradually to a saffron hue, or to violet, as some of theobservers asserted According to Mrs. Airy, the effect produced waslike looking at objects through a very dark greenish glass |.

It is manifest that the aspect of terrestrial objects cannot fail to be affectedby the change of colour which the atmospheric light undergoes during theprogress of an eclipse. It cannot be doubted, however, that the phe-nomena above mentioned are, to a considerable extent, attributable to theinfluence of contrast. Moreover, it is to be remarked that the physio-logical constitution of the eye tends to produce a modifying effect uponthe specific hue of objects. Under these circumstances, it would obviouslybe premature to make such observations as those above cited, the ground-work for deducing any sound conclusions of a general nature.

The darkness which prevails during a total eclipse of the sun is not soprofound as might be expected, nor as it is generally supposed to be.Ferrer, in his account of the total eclipse of 1806, states, that even whenthe effect produced by the interception of the solar rays was at itsmaximum, the light which still remained, was equal to that of the fullmoon§. In general, it has been found that the darkness is sufficientlyintense to prevent a person from reading, although there have not beenwanting several instances of a contrary nature. Mr. Airy has remarkedthat the illumination during the total eclipse of 1842 was so small, thathe could with difficulty read the divisions on the watch-plate, which waswithin eight inches of his eye. The faint visibility which continues tosubsist even when the sun is totally concealed behind the dark body ofthe moon, arises mainly from the light reflected by those regions of theatmosphere which are still illuminated by the direct rays of the sun. Itis evident, however, that the corona around the moon will also contributein some degree towards producing the effect. The observation of DonUlloa, relative to the darkness which prevailed during the total eclipse of1778, is very decisive upon this point. It has been mentioned that atthe commencement of the total obscuration he was enabled to perceivethe stars of the second magnitude, but that, after the appearance of theluminous ring, only those of the first magnitude were visible.

* Annuaire, 1846, p. 291.

1 Giornale dell’ Istituto del Lomb., tome iv., p. 304.

f Mem. Ast. Soc., vol. xv„ p. 17. In thus using the liberty of divesting the obser-vation cited by Mr. Airy, of the anonymous character in which he has presented it in hispaper on the eclipse, the author pleads the example of M. Arago, upon whose authorityalone he has been induced to adopt a course which is at all times desirable, but moreespecially so when the subject is of an historical nature, as it happens to be in the pre-sent instance.

§ Trans. Amer. Phil. Soc., vol. vi., p. 266.