316 



SCIENCE. 



[Vol. VI., No. 140. 



the use of the organization referred to above, but 

 "the limited time will not permit of their being got- 

 ten ready for use on this occasion. The results 

 of the observations made will be looked for with 

 interest. 



At the national museum the employes have 

 been busy for some time in arranging the exhibits 

 received from the New Orleans exposition. Many 

 of these were sent from the museum originally, 

 and are only now being returned to their places ; 

 but many were not, and, in fact, it is stated that 

 the museum has been a great gainer in the opera- 

 tion. It is said that one thousand boxes were sent to 

 New Orleans, and that two thousand have been 

 received from there, aU of which goes to prove 

 that the officers of the museum, and particularly 

 its representatives at New Orleans, are alive to the 

 interests of the great and rapidly growing collec- 

 tion, and is also conclusive evidence that a rolling 

 stone does sometimes gather moss. Z. 



Washington, D. C, Oct. 5. 



LETTERS TO THE EDITOR. 



♦♦♦ Correspondents are requested to he as brief as possible. The 

 xvr iter's name is in all cases required as proof of good faith. 



The color of the sky. 



I read with interest the communication of Prof. 

 E. L. Nichols on the above subject pubHshed in 

 Science September 11. As the views there expressed 

 (that the color is really only a subjective phenomenon) 

 run quite counter to those g-enerally held, it seemed 

 desirable if possible to confirm or disprove them. 

 Everyone who has used a spectrophotometer is well 

 aware that it is an instrument with which it is im- 

 possible, even when most carefully handled, to obtain 

 results of great precision. It, therefore, seemed to 

 me preferable to compare directly the colors of the 

 sky, and the illuminated sheet of paper. 



For this purpose I employed a polarimeter, con- 

 sisting of a tube furnished with a double image prism 

 at one end, and a revolving Nicol prism at the 

 other. Before it, in the sunlight, was laid a mirror, 

 half of which was covered with a sheet of white 

 paper. Between these and the instrument was 

 placed a sheet of black paper suitably screened from 

 the sunlight, and containing two square holes, 

 through one of which the illuminated paper was seen, 

 and through the other the blue sky reflected in the 

 mirror. The instrument was then used in the ordi- 

 nary manner, being so placed that one of the images 

 ■of the illuminated paper was in contact with the 

 oppositely polarized image of the reflected sky. The 

 Nicol was then turned till the two were of the same 

 brilliancy, and the colors compared. There was no 

 question but the sky was decidedly the bluer of the 

 two. The tube carrying the double-image prism was 

 then rotated about its axis through 180°, to allow for 

 any difference of color which might have been intro- 

 duced by the polarization, no appreciable change, 

 however, was noted. The white paper was next re- 

 moved, and some of a bluish tint substituted, but it 

 was not until paper of a decided sky blue color was 

 employed, that an accurate match could be obtained. 

 Since then the color of the reflected sky matches that 



of blue paper illuminated by direct sunlight, and does 

 not match that of white paper so illuminated, it seems 

 clear that the color of the sky is something distinctly 

 inherent to itself, and is not a subjective phenomenon 

 as supposed. 



Further evidence bearing upon this subject, col- 

 lected by Prof. E. C. Pickering from polarimetric 

 observations of the sky will be found in the Proceed- 

 ings of the American academy, vol. ix., p. 20. 



Wm. H. Pickering. 



Woodhead and Hare's ' Pathological mycology.' 



Permit me to add a few corrections to those re- 

 cently made by a correspondent concerning this pub- 

 lication, {Science, Aug. 14). The authors state on p. 

 17 that "in artificial media it is a frequent ex- 

 perience to find organisms destroyed by the virulence 

 of their own products before all food material has 

 been exhausted." I doubt very much whether this 

 observation has ever been made. A priori it seems 

 unreasonable to suppose that bacteria would commit 

 suicide so speedily. It is well known that the pro- 

 ducts of fermentation may check the process after a 

 time, but the organisms survive for some time after. 

 Pasteur's method of attenuating the virus of fowl 

 cholera depends on the act of allowing months to 

 elapse before a new culture is made. I have still to 

 find a microbe which dies in a liquid medium within, 

 at least, two months after inoculation. 



The authors seem to think that when fluids are not 

 albuminous they will not adhere to the coverglass 

 when dried and heated, hence the method of irriga- 

 tion is recommended (p. 46). As the method of 

 staining on the coverglass is of fundamental import- 

 ance, it seems strange that such a statement should 

 be made. In fact the dried layer from albuminous 

 fluids is very apt to be washed away, while the 

 ordinary 'broth,' from which probably all albumen 

 has been precipitated by heat in sterilizing, always 

 forms a firm layer. I doubt whether any one will 

 succeed well in staining and washing bacteria by 

 irrigation. They will, very likely, find their way 

 to the blotting-paper used to stimulate the current. 

 Had the authors followed Koch, as closely here as 

 elsewhere, this error would not have occurred, as he 

 is very explicit on this point. 



In the formula, for Cohn's fluid given on p. Ill 

 ' as recently modified,' we find, by comparing with 

 the most recent foreign publications (Zopf, Fliigge, 

 Hiippe, Cornil and Babes) that the quantity of all the 

 salts but one is from ten to twenty times too great. 

 It would be desirable to know to whom the modifica- 

 tion is due. I do not believe that bacteria, parasitic 

 or saprophytic, would appreciate such a concentrated 

 solution. 



There are many indications throughout the work 

 that the methods and processes described were not 

 fully mastered by the authors themselves. Thus, on p. 

 75, filters are to be washed with 'boiled distilled water,' 

 even though the filtered gelatine must be subsequently 

 sterilized by steaming the stock flasks for fifteen 

 minutes (p. 76) which is, at least, five minutes too 

 long, and would certainly ruin the gelatine. After 

 removing the potatoes from a solution of mercuric 

 chloride (p. 62), why not rinse them in boiled distilled 

 water, where its employment might do some good ? 

 Finally, the use of caustic potash or turpentine for 

 cleaning slides (p. 51) seems a rather unpardonable 

 suggestion. Theobald Smith. 



