1855.] 



THE SOLAll ECLIPSE OF 1854. 



181 



cisively confirmed by the evidence of several in the observations 

 at Toronto. 



As the annularity approached, the landscape assumed a pe- 

 culiar sombre hue, diifering sensibly, though in what it is hard 

 to say, from the shades of evening, or of a sky overcast with 

 clouds, and during the annularity that strange lurid appearance, 

 so often remarked, rested on terrestrial objects, giving to the 

 grey stone buildings of the Fort a greenish tinge, and making 

 the faces of individuals look ghastly and corpse-lLke. 



It will be collected from what has preceded, that the changes 

 of coloration refeiTcd to, though varying in detail on different 

 occasions, and even variously represented by different persons 

 at the same time and place, present some features in which all 

 agree, such as the red or orange tinge on the horizon, the 

 purple gray of the zenith, and the lurid green of light-coloured 

 terrestrial objects. The question arises — Can these circum- 

 stances be accounted for, considering them as due to the vary- 

 ing action of the sun's light on our atmosphere ? or are we to 

 infer that the quality of the sun's light is different at different 

 points of his disc ? To the latter we are able to reply in the 

 negative; for in this case the solar spectrum formed by refracting 

 the sun's rays through a prism would undergo modification in 

 color during the progress of the eclipse. The experiment was 

 tried on this occasion by Dr. Smallwood, who states that " the 

 spectrum exhibited a very slight increase of the red ray," which 

 is sufficiently accounted for by the descent of the sun towards 

 the horizon. Conclusive as this is, another test of the same 

 might have been afforded by an observation suggested bj' the 

 Committee, namely — an examination of the coronae formed oc- 

 casionally when a light cloud or haze interposes before the sun's 

 disc. The colors of these rings (first recognized by the cele- 

 brated Young as a problem of interferences on the undulutory 

 hypothesis of light) would have varied from those of the un- 

 eclipsed sun ; but the circumstances favourable to their occur- 

 rence appear to have been wanting on the present occasion. 



Dismissing, then, the hypothesis of any sensible variation 

 in the quality of the sun's light in different points of his sur- 

 face, it remains only to see if the observed facts can be accounted 

 for as atmospheric phenomena. The whole' question of the 

 illumination of the sky is one of great subtlety and delicacy, 

 and to the sagacity of the great Newton we owe the funda- 

 mental idea of its explanation, namely — " that the particles of 

 the atmosphere have no proper colour of their own, but that 

 they more easily reflect the blue and transmit the red raj-s of 

 the white solar beam." So that of a pencil of parallel rays 

 falling on a spherical particle of air or vapour, one part is 

 transmitted, another is reflected in all directions as if the par- 

 ticle itself were a source of radiant light ; in the former, the 

 colours towards the red end of the .spectrum predominating; in 

 the latter, those towards the blue. It is to this reflection or 

 scattering we owe the general blue colour of the heavens, the 

 illumination of twilight, and the diffusion of light in the day- 

 time. " Were it not for this," saj's Ilcrschel, " no objects 

 would be visible to us out of direct sunshine ; eveiy shadow of a 

 passing cloud would be pitchy darkness ; the stars would be 

 visible all day ; and every apartment, into which the sun had 

 not direct admission, would be involved in nocturnal obscurity." 

 Suppose, now, a spectator to direct his sight towards one point 

 of the sky, his eye will receive from the aerial particles along 

 the line of vision, first — those rays of the sun which, falling on 

 them after direct passage through the atmosphere, are reflected 

 to the eye ; .secondly, those, also, which, having been already 

 reflected one or more times among the whole mass of particles 



of the atmosphere, have also fallen on this line of particles, and 

 been by them again reflected in the same direction as the former 

 to his eye. 



The colour of the spot of .sky at which he looks will be de- 

 termined by the combination ol' these two lights, which we may 

 distinguish by the terms "direct" and "indirect;" the 

 former being, under ordinaiy circumstances, much the stronger 

 of the two, and giving the character to the colour. This direct 

 light, as already stated, loses its blue by transmission and its 

 red by reflection, so that the final tint, on reaching the eve, 

 and by consequence, also, the colour of the sk}-, will depend on 

 the length of path and the density and moisture of the strata 

 traversed by it. Thus, under all circumstances, in a clear skv, 

 the zenith will be decidcdij' bluer than the horizon, the blue 

 tint diminishing as we descend, both on account of the smaller 

 vertical height compared with the horizontal range of'' the air, 

 and also on account of the increased density and moisture of 

 the strata nearest the earth's surface. 



Again, at mid-day, when the sun is at his highest, the length 

 of path for the zenithal regions will then be the shortest, and 

 the blue-tint of the zenith will be stronger than at anj- other 

 time of day, and on the horizon, for similar reasons, a grey 

 tint prevails, often nearly white. As the sun descends, the 

 blue in the zenith fades, and the red predominates on the 

 horizon, till at sunset the direct light transmitted through the 

 lowest strata of air, often charged with moisture, furnishes on 

 the horizon, in the neighbourhood of the sun and extending 

 from him on both sides, a brilliant red, which whitens towards 

 the zenith, and may often be seen to assume, as we ascend, 

 the successive colours of the spectrum from red to blue-gray. 

 Opposite to the sun may often be seen a patch of red light, 

 which attains its greatest intensity just as the sun sinks below 

 the horizon, and is even more decided than that in the west, 

 the rays forming it having twice had to traverse the lowest 

 stratum of air and vapour. When the sun sinks below the 

 horizon, the direct light is intercepted fi'om the east by the in- 

 terposition of the earth, whose shadow is projected on the .sky 

 in the form of a circular segment ; the sky within this is illu- 

 minated solely by the indirect light which has proceeded by 

 reflection through the higher strata, and is consequently blue, 

 rendered still more marked by contrast with the surrounding 

 red. When the sun has sunk, and the direct light is wholly 

 cut off, the only illumination of the heavens is by the indirect 

 which, as night proceeds, is given by more and more nu- 

 merous reflections, and becomes in proportion more and more 

 blue. Applying the same explanation to the effect produced 

 by the opaque body of the moon intei-posing between the sun 

 and spectator, we see that in a partial eclipse, the direct light 

 being more or less cut off, the indirect becomes proportionallj- 

 of more importance, and has more effect in determining the re- 

 sultant colour of the portion of sk}- considered. It is also 

 evident that its effect must depend much on the altitude of 

 the sun at the time, and the position of the spectator in the 

 shadow. In the zenith tlie direct light being intercepted more 

 or less, we should expect the blue to be more decided, and if 

 the sun he somewhat low in the heavens, this blue would be 

 mixed with the indirect rays from the horizon, and thus ac- 

 quire a purple tint. On the horizon, again, the part in deepest 

 shadow loses not only its direct light, but also that portion of 

 the indirect which is ordinarily furnished to it by the zenithal 

 regions ; its remaining illumination coining from strata lower 

 down would necessarily show tlie red tint so constantly observed. 

 For intermediate portions of the sky, the prevailing tint would 



