Febeuaey 19, 1897.] 



SCIENCE. 



Sll 



person, is occupied by red, yellow and green. 

 Nevertheless, it is stated in twenty text-books 

 that the sensations of the color-blind furnish 

 exceedingly strong, if not convincing, evidence 

 of the truth of the Young-Helmholtz theory. 

 Moreover, the belief that the warm color is 

 either red or green has become so ingrained 

 that the cases by which it has been shown be- 

 yond question that it is in fact yellow have 

 failed to produce any effect whatever. There 

 is hardly a physicist, and there are very few 

 physiologists, in the English-speaking world 

 who do not still hold to this belief; as recent 

 instances, we may cite the Century Dictionarj' 

 and Johnson's Cyclopaedia (both of which are, 

 in general, of good authority in scientific mat- 

 ters), and the recent extensive memoir on color- 

 blindness by Abney and Testing in the Philo- 

 sophical Transactions. These last authors say 

 that the examination of color-blind persons is 

 of prime importance for testing any theory of 

 color vision, and, nevertheless, they are con- 

 tent, like so many others, to infer the sensa- 

 tions of the color-blind from a theory which 

 they have already adopted. 



But as early as 1856 there was one man who, 

 himself color-blind, had convinced himself that 

 his own sensations were blue and yellow, and 

 he should have convinced all the world as well 

 if the world had been open to reason — if it had 

 not been preoccupied with a theory. This man 

 was William Pole, F. R. S., professor of civil 

 engineering in University College. His papers 

 on the subject were published in the Philosoph- 

 ical Transactions ; his argument is exceedingly 

 ingenious and it is little to the credit of the 

 reasoning public that it did not make headway. 

 Had it appeared a few years earlier than it did, 

 it is probable that the Young-Helmholtz com- 

 bination would never have been formed. Pro- 

 fessor Pole preserves the interest in the theory 

 of color visions which he felt forty years ago, 

 and he is the one person, so far as I know, who 

 has discussed Helmholtz's late profound mathe- 

 matical contributions to the subject. 



The history of opinion regarding color-blind- 

 ness presents, therefore, this series of occur- 

 rences : 



1. A deduction from a theory was taken for 

 a fact. 



2. That supposed fact was taken as confirm- 

 ing the theory. 



3. The same supposed fact was held so 

 strongly that the highly ingenious reasoning 

 by which Professor William Pole showed it to 

 be erroneous forty years ago failed to awaken 

 attention. 



4. Moreover, the cases of monocular color- 

 blindness, by which it is absolutely contra- 

 dicted, and which date from fifteen years ago, 

 are without effect upon it, with most people, 

 even at the present day. 



Cheistinb Ladd Feanklin. 

 Baltimore, Md. 



SCIENTIFIC LITERATURE. 

 Non-Euclidean Geometry, or The Science of Abso- 

 lute Space. By John Bolyai. Translated 

 from the Latin by Db. Geoege Bruce Hal- 

 STED. Austin, Texas, the Neomon. 

 This book of John Bolyai was published in 

 an appendix to a work of his father's in 1882 — 

 within the memory of many men now living. 

 The same date marks the publication of Fara- 

 day's experiments in the science of electricity, 

 which revolutionized the whole theory of elec- 

 tricity and gave to the world the dynamo. 

 Faraday's conception of electricity as an action 

 that pervades all space like that of light and 

 heat, and the later identification by Herz of all 

 three phenomena as very probably different 

 phases of one and the same action, is not more 

 strange, new, or revolutionary, than Bolyai's 

 science of absolute space. We are indebted for 

 this English translation to the zeal, energy and 

 ability of Dr. Halsted, who has long labored in 

 this field of mathematics. 



What is this science of absolute space ? Those 

 who wish to know in detail should get the book 

 and read it carefully. The translator's intro- 

 duction contains a complete historical summary, 

 and the earlier portions of the work are within 

 the comprehension of every student of elemen- 

 tary geometry. In general, Bolyai has shown 

 that the geometry of Euclid is an hypothesis ; 

 that there are an infinite number of geometries 

 equally probable with Euclid's, and that which 

 of these coincides with the true properties of 

 the space in which we live can be determined 



