May 12, 1892] 



NATURE 



Ih 



qualiiy heat, which, being of itself motion, compels 

 us to infer that a molecule in motion without any 

 force to restrain or qualify it, is in every respect to be 

 considered as a free projectile. Allow such free pro- 

 jectiles to be endowed with perfect elasticity, and likewise 

 extend the same property to the elementary parts of all 

 bodies that they strike against, and we immediately 

 introduce the principle of the conservation oivis viva to 

 re.i^ulate the general effects of their fortuitous encounters. 

 \\hether gases do consist of such minute elastic pro- 

 jectiles or not, it seems worth while to inquire into the 

 physical attributes of media so con«-tituted, and to see 

 what analogy they bear to the elegant and symmetrical 

 laws of aeriform bodies. 



" Some years ago I made an attempt to do so, pro- 

 ceeding synthetically from this fundamental hypothesis, 

 and have lately obtained demonstration of one or two 

 points where the proof was then deficient. The results 

 have appeared so encouraging, although derived from 

 very humble applications of mathematics, that I have 

 been led to hope a popular account of the train of reason- 

 ing may not prove unacceptable to the Royal Society. — 

 September i, 1845." 



REPORT OF THE ROYAL SOCIETY'S COM- 

 MITTEE ON COLOUR VISION. 



A COMMITTEE, consisting of Lord Rayleigh as 

 ■^*- Chairman, Lord Kelvin, Mr. Brudenell Carter, Prof. 

 Church, Mr. J. Evans, Dr. Farquharson, M.P., Prof. 

 Michael Foster, Mr. Galton, Dr. Pole, Sir G. Stokes, 

 and Captain Abney, as Secretary, was appointed by the 

 Council of the Royal Society in March 1890, to consider 

 the question of testing for defective colour vision. Their 

 report has just been presented to the Royal Society, and 

 it possesses great practical interest for all classes, con- 

 sidering that on the average one male out of every 

 twenty-five suffers more or less from this form of blindness. 



The Committee have taken evidence as to the tests in 

 general use on the railv\ ays, and also as to those which have 

 been for some time adopted by the Board of Trade for 

 the mercantile marine service, and have supplemented it 

 by carrying on practical examinations on their own 

 account. Experts have also given evidence as to the 

 different forms of colour-blindness to be found, and the 

 fact that it may be induced by disease as well as be 

 congenital has been brought prominently forward by Dr. 

 Priestley Smith, of Birmingham, and Mr. Nettleship, of 

 St, Thomas's Hospital, and we have it on their authority 

 that this type is not a negligible one. As an outcome of 

 their investigations, the Committee have unanimously 

 agreed to the following recommendations : — 



(i) That the lioard of Trade, or some other central 

 authority, should schedule certain employments in the 

 mercantile marine and on railways, the filling of which by 

 persons whose vision is defective either for colour or form, 

 or who are ignorant of the names of colours, would involve 

 danger to life and property. 



(2) That the proper testing, both for colour and form, 

 of all candidates for such employments should be com- 

 pulsory, 



(3) That the testing should be intrusted to examiners 

 certificated by the central authority. 



(4) That the test for colour vision should be that of 

 Holmgren, the sets of wools being approved by the 

 central authority before use, especially as to the correct- 

 ness of the three test colours, and also of the confusion 

 colours. If the test be satisfactorily passed, it should 

 be followed by the candidate being required to name 

 without hesitation the colours which are employed as 

 signals or lights, and also white light. 



NO. I I 76, VOL. 46] 



(5) That the tests for form should be those of Snellen, 

 and that they should be carried out as laid down in 

 Appendix VI. It would probably, in most cases, suffice 

 if half normal vision in each eye were required. 



(6) That a candidate rejected for any of the specified 

 employments should have a right of appeal to an expert 

 approved by the central authority, whose decision should 

 be final. 



(7) That a candidate who is rejected for naming colours 

 wrongly, but who has been proved to possess normal 

 colour vision, should be allowed to be re-examined after 

 a proper interval of time. 



(8) That a certificate of the candidate's colour vision 

 and form vision according to the appointed tests, and his 

 capacity for naming the signal colours, should be given 

 by the examiner ; and that a schedule of persons 

 examined, showing the results, together with the nature 

 of the employments for which examinations were held, 

 should be sent annually to the central authority. 



(9) That every third year, or oftener, persons filling 

 the scheduled employments should be examined for 

 form vision. 



(10) That the tests in use, and the mode of conducting 

 examinations at the different testing stations, should be 

 inspected periodically by a scientific expert, appointed 

 for that purpose by the central authority. 



(11) That the colours used for lights on board ship, and 

 for lamp signals on railways, should, so far as possible, 

 be uniform, and that glasses of the same colour as the 

 green and red sealed pattern glasses of the Royal Navy, 

 should be generally adopted, 



(12) That in case of judicial inquiries as to collisions 

 or accidents, witnesses giving evidence as to the nature 

 or position of coloured signals or lights should be them- 

 selves tested for colour and form vision. 



These recommendations have been framed after duly 

 weighing all the evidence they have collected, and from the 

 results of the experiments they have carried out during the 

 last two years : and the reasons for adopting them are set 

 forth at some length in the report. The Committee have, 

 perhaps wisely, refused to endorse any particular hypothesis 

 of colour vision, though they have described two, those 

 of Young and Hering, in some detail, no doubt con- 

 sidering that everything which might be debatable had 

 better be avoided when practical recommendations alone 

 were in question. It is, however, a matter of some regret 

 that this should be the case, as a Committee so strongly 

 constituted should have been able, if not to convince 

 every one, at least to lead opinion into proper channels. 

 What httle they have said in the notes to the report leads 

 one to suspect that they are not satisfied that either 

 Young or Hering has given a theory which will satisfy 

 all requirements. Leaving, however, the question of 

 theory, we may point out that the practical necessity of 

 insisting, on the grounds of public safety, that 

 certain posts on railways and on board ship 

 should only be filled by persons possessing normal 

 colour vision, no sane man would call in 

 question. The peril that must arise, for instance, if 

 an engine-driver could by any possibility mistake a red 

 signal of danger for a green signal of safety, or if a look- 

 out man on board ship should be liable to make a similar 

 error, is self-evident ; and it is to prevent any such 

 risks being run that the Committee buckled to the task of 

 recommending tests which should be efficient and per- 

 fectly trustworthy. There has been for a long time a 

 suspicion, if not more than a suspicion, that the examina- 

 tions carried on for colour vision by the Board of Trade 

 in the mercantile marine were inadequate in both re- 

 spects ; and what little was known regarding the tests em- 

 ployed by the various railway companies engendered the 

 same feeling of distrust, in those who had considered the 

 subject in a scientific spirit. The evidence shows that 

 the Board of Trade examiners have passed on a second 



