HISTOBY OF PHYSICAL ASTEONOMY.

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be too feeble to render her surface visible. The records of lunar eclipsespresent several examples of this kind. Thus Kepler states that during thelunar eclipse which happened on the loth of June, 1620, the moon totallydisappeared, although the fixed stars of the fourth and fifth magnitudes inher immediate vicinity were plainly distinguishable *. Hevelius also men-tions that during the lunar eclipse of April 25, 1642, the place of the mooncould not be ascertained even with the aid of the telescope, although theair was sufficiently pure to discern the stars of the fifth magnitude f.

The account given by Wargentin, of the lunar eclipse of May 18, 1761, asobserved by him at Stockholm , furnishes an interesting illustration of thesame remark. The total immersion of the moon took place at 10 h 41™p.m.The part of the margin of the lunar disk which had last entered the shadowwas pretty conspicuous by means of a bright light for five or six minutesafter the immersion, and to the naked eye exhibited a lustre equal tothat of a star of the second magnitude; but at 10 h 52 m , this part, aswell as the whole of the rest of the moon’s body, disappeared so com-pletely, that not the slightest trace of any portion of the lunar disk couldhe discerned either with the naked eye or with the telescope, although thesky was very clear and the stars in the vicinity of the moon were distinctlyvisible in the telescope. After a long search for the missing body of themoon, the Swedish astronomer at length discovered it at ll h 30 m with atwo-feet telescope, by means of a faint light which was visible about theeastern border of the disk. At ll h 33 m , persons of acute vision were ableto discern a trace of it with the naked eye, like an exclusively thin vapour;but more than half of the disk was still invisible. The boundary betweenthe visible and invisible portions was very irregular; the light was also moreintense at the margin of the moon than it w r as towards the centre. Duringthe progress of the emersion, which commenced at 12 h 15 m , the part ofthe moon which was still involved in the earth’s shadow was by no meanspalpable to observation, as is usually the case on similar occasions J.

If the region of the atmosphere, through which the solar rays pass, beeverywhere very transparent, the red rays will be transmitted to the moonin great abundance, and her surface will, in consequence, appear stronglyilluminated. Thus, during the lunar eclipse of December 22, 1703, themoon, when totally immersed in the earth’s shadow, was visible at Avignon by a ruddy light of such brilliancy, that one might have imagined her bodyto be transparent, and to be enlightened by the sun from behind §. Asimilar appearance was remarked on the occasion of the total eclipse ofthe moon, which happened on the 19th of March, 1848. Mr. Forster, ofBruges , states, in an account of the eclipse, that during the totality of theimmersion, the light and dark places on the face of the moon could be almostas well made out as in an ordinary dull moonlight night. So intense wasthe illumination of the moon’s surface, that many persons could not bepersuaded that she really was eclipsedj|. Mr. Walkey, who observed theeclipse at Clyst St. Lawrence, near Collumpton, states that the appearancewas as usual until 20 minutes to nine, when the whole of the moon’s sur-face became very quickly and very beautifully illuminated, so as toresemble the glowing heat of fire from the furnace, rather tinged with adeep red. This appearance lasted about an houi'IT.

Sometimes it happens that the region of the terrestrial atmosphere

* Ep. Ast., p. 825. + Selenographia, p. 117. J Ph. Tr., 1761, pt. i., p. 208, et seq.

§ Mem Acad, des Sciences, 1704, p. 59. (Hist.)

II Monthly Proc. Ast. Soc., vol. viii., p. 132.

^ Ibid., vol. viii., p. 132. “ More than threescore years have passed willi myself,”