436 



SCIENCE. 



[Vol. V., No. 121. 



and living well, but involved in the cares, and bur- 

 dened with the responsibilities, of great business 

 enterprises — are more liable than other men to 

 break down and die at about these latter ages." The 

 comparison here instituted — between Americans who 

 belong to the classes to which Herbert Spencer's stric- 

 tures chiefly refer, and other Americans — seems much 

 more likely to lead to 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. Huggins's communica- 

 tion in Science for May 15, I think he fails to un- 

 derstand a point I particularly emphasized in my 

 communication of April 3; namely, that I was not 

 criticising his work, but merely stating the results of 

 my own investigations. I have not, as yet, had an 

 opportunity to experiment with a reflector ; but, when 

 we consider the greater visibility of minute compan- 

 ions of bright stars in refractors as compared with 

 reflectors, it does not seem evident how chromatic 

 aberration and internal reflection from the surfaces of 

 a lens can totally unfit it for work, which, accord- 

 ing to Dr. Huggins, is perfectly possible for a reflector. 

 In the mean time, an account of some experiments 

 which I have recently made with my refractor may 

 be of interest. 



Dr. Huggins suggests that the dark fringe on the 

 negative, which was obtained around the sun, is 

 largely due to diffraction at the instants of opening 

 and closing my shutter. If this were so, the darken- 

 ing should extend farthest, and be most marked in 

 the direction parallel to the line of motion of the 

 shutter, and should be almost nil in the direction at 

 right angles to this 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, is not of practical impor- 

 tance with my apparatus. The real causes which 

 would tend to produce a dark fringe around the sun's 

 image are fourfold, and may be classified as follows: 

 (a) the solar corona, (b) the atmospheric reflection, 

 (c) instrumental defects, (d) photographic properties 

 of the plate. In the last class I include chemical re- 

 duction of the particles of the silver salt contiguous 

 to reduced particles of metallic silver; also halos pro- 

 duced by insufficient backing, and irregularities in 

 the film itself. At the time of a partial solar eclipse, 

 the effect of the corona alone is removed from around 

 a portion of the sun's limb, the other three causes 

 of the darkening remaining. By photographing the 

 sun when its 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 sun's 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- 

 portance of each determined. 



Dr. Huggins claims that my results are due almost 

 wholly to instrumental defects, and not to atmospheric 

 reflection. In this I think he is mistaken. The dark 

 fringe is in part due to both causes ; but, even in the 

 clearest weather, the part due to atmospheric reflec- 

 tion is still prominent. Dr. Huggins says, "When 

 the sky is free from clouds, but white from a strong 

 scattering of the sun's light, the sun is well defined 

 upon a sensibly uniform 1 surrounding of air-glare, but 

 1 The italics are ray own. 



without any indication of the corona. It is only 

 when the sky becomes clear and blue in color that 

 •coronal appearances present themselves with more or 

 less distinctness." I 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 every 

 one knows, whether the sky is clear or hazy, that 

 portion of it in the immediate vicinity of the sun is 

 considerably brighter than those portions more re- 

 mote. To test the matter photographically, on a 

 hazy day such as he describes, I took a picture of the 

 sun when it was half hidden behind a high building. 

 If, as he claims, the dark fringe was due solely to 

 instrumental defects, it should be equally well marked 

 all round the semicircular image of the sun. If, on 

 the other hand, it were due solely to atmospheric 

 reflection, the part protected by the chimney should 

 be entirely devoid of halo. On development, a very 

 strong halo surrounded the sun's image, going as 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 increase 

 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 corona-like 

 fringe shown in my photographs is due to causes 

 outside of the instrument, 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 that 

 the effect of the corona was imperceptible as com- 

 pared with the effect of the other sources of light, 

 although the atmospheric conditions were exception- 

 ably favorable. On a clear day the atmospheric re- 

 flection is less marked than on a hazy one, but is still 

 always present. I hope soon to repeat the experi- 

 ment with an instrument closely resembling that of 

 Dr. Huggins, although the advantages of his form of 

 apparatus do not seem very evident to me. 



There are one or two points raised in Dr. Huggins's 

 article which should be answered here. As stated in 

 Science, April 17, all thejplates employed were backed 

 with asphalt varnish. The image of the sun obtained 

 through the violet glass was not reversed, although 

 there is no question but that it would have been, as 

 Dr. Huggins suggests, by a longer exposure. I did 

 not care "for a 'different result,' and merely made 

 the statement as one of the facts observed under the 

 conditions named. Dr. Huggins objects to my refer- 

 ence to Dr. Lohse, maintaining that his 'published 

 statement reads differently.' But, in fact, Dr. Lohse 

 only states, that, after overcoming certain difficulties, 

 results were obtained which justify a continuation of 

 the experiments. He does not state that he considers 

 his results coronal, but merely that a continuation of 

 the experiments would be desirable, in which state- 

 ment I thoroughly agree with him. As I do not 

 feel at liberty to print a private letter, I have written 

 to Dr. Lohse for an exact expression of his views. 



Wm. H. Pickering. 



Institute of technology, Boston, Mass. 



A BRONZE MEDALLION PORTRAIT OF 

 DR. ASA GRAY. 



We present to our readers on the opposite 

 page a faithful copy of the admirable bronze 

 medallion, by Saint Gaudens, of Professor Asa 



