March i, 1889.] 



SCIENCE. 



171 



Most cases of color-blindness are found to be congenital, and are 

 incurable. Many have been produced by disease, some by violent 

 concussions in accidents, and some by excessive use of tobacco 

 and alcohol. Temporary blindness to violet m^ay be induced by 

 santonine. From these facts several interesting questions have 

 suggested themselves to us. If color-blindness follows the law of 

 heredity, is it on the increase, or decrease ? Further, is it a prod- 

 uct of civilization ? The first of these queries can be answered 

 only by statistical data extending over long periods of time. The 

 second naturally suggests a comparison, first, of the color-sense of 

 civilized nations among themselves ; and, second, of civilized with 

 uncivilized peoples. Of tests in native tribes, we can find but two 

 recorded, — those of Dr. Favre on some tribes in Algiers, and 

 those of a Dr. Fox on 150 American Indians, but where we do not 

 know. 



First, for the comparison of civilized tribes among themselves, 

 we have calculated the following percentages from tables reported 

 by Dr. Jeffries : — 



Austria 



Denmark 



Belgium 



Holland 



Finland 



Norway 



Sweden 



Switzerland 



Germany 



Russia 



Italy 



England 



United States 



Average per cent 



3 79 

 3-74 

 413 



3 73 

 5.36 



3.76 



No great reliance can be placed upon these results. The numbers 

 examined are too small, the methods of testing not uniform, not 

 equally reliable. However, the probabilities of error are about 

 equally distributed ; so that the conclusion is fairly well established, 

 even without great accuracy of data, that among civilized nations 

 color-blindness is at present almost equally common. 



Second, among uncivilized people. Dr. Favre's results from Al- 

 giers, already alluded to, show 414 examined, and only 2.6 per 

 cent color-blind. Dr. Fox reports 161 young* Indians tested, and 

 only 1. 81 per cent color-blind. These percentages, so low com- 

 pared with those for civilized people, suggested to us that color- 

 blindness may be a product of civilization, and have led to our tests 

 here reported. At the Haskell Institute at Lawrence, Kan., are 

 several hundred Indians, representing many tribes. These we 

 have recently examined by Holmgren's method with Berlin 

 worsteds. Out of 418 tested, — 285 males and 133 females, — onlv 

 three cases of color blindness exist, or only .7 of one per cent. 

 These three are full blooded Indians of the Pottawattamie, Pawnee, 

 and Crow tribes. Of these, two have defective color-sense for red, 

 and one for green. 



The Indians of the school are about equally divided as full-bloods 

 and half-breeds. It seemed to us that the half-breeds showed 

 more instances of blunted color-sense than the full-bloods. This 

 was evidenced in more frequent and prolonged hesitation among 

 them in comparing the colors than among the full-bloods. If this 

 be confirmed by more extended examinations, it would, in con- 

 junction with the low percentages obtained as above, be an argu- 

 ment in the theory proposed by us that defective color-vision is in 

 some way the product of civilization. 



The use of tobacco suggests itself as a possible cause. This 

 would explain also the low percentage among females. It leads 

 also to the thought of increase of color-blindness in males in future 



generations. But the data are at present too meagre to more than 

 suggest this explanation. 



It is certainly not accidental that nearly every case of color- 

 blindness is for red, few for green, and seldom one for violet. Why 

 are the defects thus limited, at present at least, to the longer wave- 

 lengths of light ? 



The Young-Helmholtz theory of color- perception will locate the 

 affection in that layer of the retina corresponding to the first of the 

 three primary sensations of color. But why this special layer, with 

 few exceptions, is the only one affected, has at present no explanation. 



The law of heredity indicates increasing sensitiveness in those 

 nerves which are subjected to special use through many genera- 

 tions. It seems reasonable to look for an explanation of the more 

 perfect color-sense in females to this fact ; but among males there 

 will probably be an increase, in future generations, of the number 

 of cases of defective color-sense. L. I. Blake. 



W. S. Franklin. 



e, Kan , Feb. 19. 



Note on the Wind-Pressure Constant. 



There is a very old formula in use among English and American 

 engineers and meteorologists for obtaining the force of the wind 

 from its velocity. The product of the square of the wind's velocity 

 in miles per hour into the factor .005 is taken as the pressure in 

 pounds upon each square foot. It is used alike at sea-level and on 

 the tops of high mountains, and in the extreme temperatures of 

 winter and of summer, notwithstanding the pressure must vary as 

 the density of the air. This is the value of the factor determined 

 by Rouse from experiment about one hundred and fifty years ago, 

 and of all the crude experiments which have been made from that 

 time to this, and before. It seems to be an extreme value. Of a 

 number of the older determinations of this factor, it is stated, in 

 Gehler's " Physicalische Worterbuch," that this is the worst, while 

 those of Hutton and Woltman are perhaps not much in error. It 

 is astonishing to see, therefore, with what tenacity engineers and 

 meteorologists still hold on to this factor. It has been maintained 

 by the writer for several years that this factor is much too large, — 

 first in Vau Nostra7id's Journal, 1881; then in "Recent Advances 

 in Meteorology ; " and in the American Meteorological Journal, 

 1887. It was shown that the theoretical value of the factor, not 

 considering friction, is .0027; and it was thought that this could not 

 possibly be increased to .005 by the friction of the air. And it was 

 shown that this view of the matter is confirmed by Loomis's results 

 obtained from the discussion of experiments made by the request of 

 Newton in St. Paul's Cathedral, London, upon the velocity of the 

 falling of hollow glass globes and of bladders, and of Hutton's ex- 

 periments with a whirling-machine. From all these researches, 

 and also the somewhat recent experiments of Hazen with a whirling- 

 machine, it was concluded that the theoretical constant above could 

 not be increased by friction more than one-tenth, or, at most, one- 

 eighth part. But the old factor has been in use so long, that conser- 

 vatives think it must be correct, and so are unwilling to give it up. 



A further confirmation of the erroneousness of the factor is now 

 found in the last number of the Quarterly Journal of the Royal 

 Meteorological Society, which contains a report from the wind- 

 force committee appointed by that society. The committee, as yet, 

 have made only a few preliminary experiments in this part of their 

 work ; but the average value of the factor from these is .003, which 

 is about one-tenth part greater than the theoretical value given 

 above. This will, no doubt, be changed a little in their final report, 

 after more experiments shall have been made ; but as it agrees 

 nearly with the factor obtained by Hazen, and with what is to be 

 inferred from other experiments, it is not probable that the final 

 result will vary much from this. 



This is a factor in which engineers are especially interested, and 

 its value ought to have been accurately determined by them long 

 ago ; but, as the Royal Meteorological Society has now taken it in 

 hand, it is to be hoped that its committee will do the work 

 thoroughly, as they apparently intend to, and determine the value 

 of this factor accurately, not only for plates of different sizes and 

 shapes, but also for different temperatures and barometric pressures. 



Wm. Ferrel. 



Kansas City, Mo., Feb. zo. 



