Page:Science vol. 5.djvu/472

 [Vol.. v., Tfo. m.

��and livine well, bul involved in the cares, and bur- dened with the responsibilities, of great bueiaest enterprises — are more liable than other roea to break down and die atabouttbese latter Ages." Tbe comparison here Instituted — between Americana who belong to the classes to which Herbert Spencer's stric- tnrea chiefly refer, and other Araerleaiis — aeems much more likely tn lead lo a reliable result than a compari- son between Americans and Englishmen. F. F.

An attempt to photograph the solar corona.

Judging by the tone of Dr. Bugslns's communica- tion in Scipne.t for May 15, 1 tliink he fails to un- derstand a point I particularly emphasized in my communication of April 3; namely, that I waEi not crlUeiaing his work, but merely slating the resiills of my own Investigations. J have not, as yet, had an opportunity to experiment with a reflector; but, when we consider the greater viBibilily of mitiul* compan- ions of bright stars in refractors as compared with reflectors, it ilocs not seem evident bow chromatic aberration and internal reflection from the surfaces of a lens can totally unfit it for work, which, accord- ing to Dr. Hugglns, is perfectly possible for a reflector. In the mean time, an account of some experiments which I have recently made willi uiy refractor may be of interesL

Dr. Huggins suggests that the dark fringe on Ibe negative, which was obtained around the sun. is lai^ly due to diffraction at the instants of opening and closing my sliuiter. If this were so, the darken- ing should extend farthest, and be most marked In the direction parallel lo the line of motion of the shutter, and should be almost nil in the direction at right angles to Ibis line. A careful inspection of my results shows no such effect, the greatest darkening lying sometimes in one direction, and sometimes in another. I therefore think that this objection, al- though theoretically sound, l» not of practical impor- tance with my apparatus. The real causes which would lend to produce a dark fringe around the suti'a image are fourfold, aud may be classifled as follows: (a) the solar cnrona. (b) the atmospheric reflection, id Inslnimental defects, (d) photographic properties of the plate. In the last class I Include chemical re- duction of the particles of Ibe silver salt contiguous lo reduced particles of metallic silver; also haloa pro- duced by linufflcient backing, and irregularities in the Aim iiseir. At the lime of a partial solar eclipse, Iheelleclof the corona atone is removed from around a portion of the stin's limb, the other three causes of the darkenlna remaining. By photographing the sun when Us disk is half hidden behind a high neighboring building, the first two causes alone of the darkening are removed. By pasting a strip of black paper across the middle of the plate In such a position that the *aii'' image shall fall, half on the paper, and half on the plate, and then, before de- velopment, removing the paper, the first three causes alone of the darkening will be removed, leaving the fourth. By these devices the effect of each of these four causes has been sifted out, and the relative Im- portuice of each determined.

Dr. Huggins claims Hint my results are due almoat wholly lo insr rumenlsl defects, and not lo almospheric reflection. In th1> 1 lliink be is mistaken. Thedark fringe is in part duf n> both causes; but, even in the clearest weather, the part due to atmospheric reflec- tion is still prominent. Dr. Hucgins says, "When the sky is free from clouds, bnt white from a strong scattering of the sun's light, the sun Is well defined njion a SMirlWu uniform ' surrounding of air-glare, but • Th" iMllc. .M roy own.

��when the sky becomes clear and blue In color that coronal appearances present themselves with mor« or less distinctness." 1 do not know what to make of this statement; for it certainly runs counter to all that one would naturally expect, to all visual experi- ence, and to all my photographic results. As erery one knows, whether the sky is clear or hazy, that portion of it In the immediate vicinity of Ihe sun la considerably brighter than those portions more re- mote. To lest the matter photographically, on a hazy day auch as he describes. I took n picture of the sun when it was half hidden behind H high building. If, as he claims, the dark fringe was due solely to instrumenlal defects, it should be equally well marfcad all round the semicircular image of the sun. If, on the other hand, it were due solely lu atmospheric reflection, the part protected by the chimney thonld be entirely devoid of halo. On development, a very slroug halo surrounded the sun's image, going aa far round as the brick wall. Here It abruptly ceased, and was replaced by a barely perceptible darkening along the straight side of the image. This Increaae of brilliancy on approaching the sun's limb was very marked. This appearance can be verified by any one visually with a piece of colored glass. It therefore appears evident that a great part of the corana-llke fringe shown in my photographs is due to canaea outside of the instniment, and hence cannot be di- minished by changes in the latter. On the photo- graphs taken at the time of the eclipse, the fringe was as strongly marked in front of the moon as on the other side of the sun. It therefore appears tlcat tbe effect of the corona was imperceptible as com- pared with the effect of the other sources of light, although the atmospheric condilious were eiceptlon- ably favorable. On a clear day the atmospheric re- fleclion is less marked than on a hazy one, but is still always present. I hope soon lo repeat ihe experi- ment with an instrument closely resembling that a — Dr. Huggins, although Ihe advantages of his form < apparalua do not seem very evident to me.

There are one or two points raised in Dr. I ,^ .._ article which should be nnswereil here. As staled i^ Sciencf, April 17, all tb elpl a tes employed » with asphalt varnish. The Image of the sun obtaiiM through the violet glass was ni>t reversed, althoug there Is no question but that It would have bem, ■

Dr. Huggins suggests, by a longer e;

not care for a 'different result,' and merely made the statement as one of ibe facts observed under the conditions named. Dr. Huggins objects to my refer- ence to Dr. Lo]i.<e, maintaining that bis 'published statement reads differently.' Bnt, In fact, Dr. Lohae only slates, that, after overcoming certain dlfficuItlM, results were obtained which justifya continuation of the experiments. He does not slate that he considers his results coronal, but merely that a continuation Ol~ the experiments would be desirable. In which stat4 ment I thoroughly agree with hlra. As I do d feel at liberty to print a private letter, I have wiltti to Dr. Lohse for an exact expression of his views.

Wai. H. PicKEBiKM

IniUtule of leehnolagy. Bd«od, "

���We present to otir readers on the oppositj page a faithful copy of the admirable broiu' mciUllion, by Saint Gaiiilens, of Professor A

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