640 



SCIENCE, 



[Vol. VIII., No. 204 



Sedgwick, De Morgan, Maria Edgeworth, and a 

 number of others, leads us to the strong wisli that 

 their correspondence might have been presented 

 in even greater fulness. We have, indeed, the 

 promise of an extended correspondence between 

 Hamilton and De Morgan in the appendix to the 

 succeeding volume of Hamilton's life. Mr. 

 Graves has considerately provided indexes to both 

 these volumes with a minuteness to suit the most 

 exacting librarian: their thoroughness, in fact, 

 nearly doubles the value of his work. The possi- 

 bility of a collection of the strictly scientific and 

 technical correspondence of Hamilton has already 

 been hinted at, and will, on the completion of the 

 present work, supplement this literary biography 

 in a most important direction. Still beyond that, 

 are the abounding mathematical remains of Ham- 

 ilton, to edit and publish which in proper form 

 would require the work of a genius little inferior 

 to that of Hamilton himself. Mr. Graves prom- 

 ises to complete his biography in the next succeed- 

 ing volume : let us hope that his promise is not 

 well grounded, and that he will give us a fourth. 



The Young-Helmholtz theory of color-sensa- 

 tion has recently been put to the test of direct 

 experimental proof by Herr Frithiof Holmgren 

 (Verhandlungen der physiolog. gesellschaft zu 

 Berlin, 1886, No. 18). As is well known, the theory 

 is that the retina contains three sets of nerve- 

 elements, each set capable of responding to the 

 stimulus of a single color alone ; and that the 

 three colors which correspond to three sets of 

 nerve-elements are green, red, and violet. These 

 are the primary colors, and our sensation of all 

 others is due to the simultaneous excitation of 

 nerve-elements of different sets. Now, it is pos- 

 sible to produce a point of light so minute that its 

 image on the retina shall have no greater dimen- 

 sions than those of a single nerve-element or 

 cone. If such a point of light in any color of the 

 spectrum be examined in such a way that its 

 image falls in turn upon different parts of the 

 retina, it will, if the Young-Helmholtz theory be 

 true, be seen only as red, green, or violet. If one 

 of these primary colors be chosen for examina- 

 tion, it will appear in its own shade or not at all ; 

 but, if any other shade is employed, it will be re- 

 solved into its primary elements, and seem red, 

 green, or violet, according to its composition and 

 the particular cone on which it falls. The results 

 of Holmgren's investigation were in entire accord- 

 ance with the theory ; red, green, and violet (in- 

 digo-violet) were unchanged ; yellow appeared 

 red, green, or colorless, in no part of the field 

 distinctly yellow ; blue was resolved similarly 

 into green and violet. Further experiments, with 



a view to determining how many cones must re- 

 ceive simultaneous stimulus to produce the sensa- 

 tion of a particular color, show that yellow is seen 

 as red or green even when the retinal ima^e is 

 considerably smaller than the section of a cone ; 

 while, to be seen as yellow, the image must be 

 large enough to cover two or three cones. 



— In a paper read before the chemical section 

 of the fifty-ninth versammlung deutsch. natur- 

 forscher zu Berlin on the 23d of September, Herr 

 Liebreich calls attention to the curious fact that 

 certain chemical reactions, which proceed readily 

 enough under ordinary conditions, are delayed or* 

 fail altogether when the liquid reagents are in the 

 meniscus of a narrow tube. Herr Liebreich is in- 

 clined to regard this phenomenon as due to cohe- 

 sion, and to conclude that certain reactions may be 

 delayed, or permanently prevented from taking 

 place, by the action of this force. Whether this 

 be the true explanation or not, the fact is a very 

 interesting one, and likely to be of the highest im- 

 portance in its bearing on physiologico-chemical 

 processes, which go on in the capillaries of the body. 

 Many reactions which are readily effected in the 

 laboratory may be altogether impossible in the 

 living organism ; and, since the character of the 

 capillary walls may be of considerable influence, 

 reactions which give normal results in the healthy 

 organ, may yield quite different products or be 

 entirely suppressed when the organ is diseased. 



— A thesis on the geology and vein-structure 

 of south-western Colorado, by Prof. T. B. Com- 

 stock of Champaign, 111., lately published in the 

 Transactions of the American institute of mining 

 engineers, is one of the few detailed geological 

 studies of a western locality, not the work of a 

 government surveyor. It contains a general ac- 

 count of the geology of the region, in greatest 

 part from original observations, and examines 

 with especial care the succession of the volcanic 

 rocks and the phenomena of mineral veins. The 

 division of the paper that will perhaps excite most 

 comment is the one that contains the author's 

 views on the relation between the direction and 

 the minerals of the veins in the Redpeak district. 

 Six zones of mineral veins radiate from the peak 

 as a centre, as follows : N. 38° E., arsenical; N. 

 79i E., bismuth ; S. 34| E., galena-gray copper; 

 S. 35 W., antimonial; S. 76i W., argentiferous ga- 

 lena; N. 36^ W., silver sulphuret. Between these 

 mineral zones there are wedge-shaped barren 

 areas, which begin to be particularly noticeable 

 along the course of the Animas River, skirting 

 around the peak. Reference is made to the criti- 

 cisms of Professor Ililseng, who does not accept 

 Mr. Comstock's views. 



