8 



K n;o w l e d g e 



[November 1, 1889. 



down " in tbe reverse of the usual order, i.e. from right to 

 left instead of from left to right. 



Ex.\.MPLE in.— Fuid the quotient of 733827l■60503-^ 748. 

 Piide. — Jfultiply all divisors ending in 3 by 7. 

 Thus we have 513679012352.1-4-5201. 

 Now multiply by 520, and point off the answer as 

 before. 



513679012352.1 

 520 



4680.9 

 4680 

 The quotient is 987654321. 



It wlQ be observed that there is here notbiag " tenta- 

 tive," as in ordinary long di\ision. In fact, tbe most 

 difficult work required is multiphcation by one figure, and 

 I liave no doubt that any intelligent child could be taught 

 to j5nd the quotient by this method much easier and more 

 quickly than by the usual one. 



Ex.\MPLE IV.— Find the quotient of 41107567 -f-9001. 

 Ride. — Di\isors ending in uiiiti/ need no multiplier. 

 Therefore x bv 900. 



411.0756.7 



6300 

 410445.6 



5400 

 40504.5 

 4500 



3600.4 

 3600 

 The quotient is 4567. 



Ex.«n>LE v.— Find the quotient of 2929559^389. 

 Rule. — Multiply divisors endmg ui 9 bv 9. 

 Thus ' 26366031-^3501. 



Now multiplv bv 350, and point off the quotient as 

 before. " " 2636603.1 



350 



3625.3 

 J050 

 6257.5 

 1750 



2450.7 

 2150 

 The required quotient is 7531. 



I have now given all the varieties which wLU be re- 

 quired, viz. dinsors ending in 1, 3. 7, or 9. 



In a future paper I purpose, with your kind permission, 

 giving a few further particulars showing the adaptability 

 of the method to all divisors whatsoever. 



COLOUR BLINDNESS. 



By Rich.\rd Beynon. 



THE first prominent case of colour blindness of which 

 we have authentic record is that of John Dalton, 

 tbe propounder of the Atomic theory. Although 

 in his Lectures on Natural Philosophy he had 

 discom'sed on the '• Doctrine of Colours," Dalton 

 did not discover his own intirniity until a later date, and 

 then quite by accident. The blooms of the geraniinn 

 appeared to him a different colour by candle-light than by- 

 day. In spite of the assurances of his friends that the 

 vivid red of the flowers was constant, to liim the blooms 

 were sky-blue by day and red by candle-hght. From this 

 discovery he was led to investigate the pecuharity of his 

 own colour \-ision by means of the solar spectrimi. As a 

 result of his researches he clearly demonstrated that there 

 are some people who experience the same sensation of 

 colour from two such opposite colours as red and green. 

 From the date of Dalton's discovery in 1794 down to a 

 few years ago, very little light was thrown upon the 

 apparent vagaries of this disease. It is true that several 

 treatises were writteu on the subject, but they treated 

 colour blindness rather as a rare and ctu-ious phenomenon 

 than a malady which had any practical bearing upon the 

 relations of every-day life. In the year 1877 public atten- 

 tion was dfrected in a very forcible manner to the practical 

 issues hinging upon colour bUnduess. In the December 

 of 1876 the railway accident commonly known as the 

 Arsley .Jimction Disaster occurred, caused by the inability 

 of a responsible person to discriminate between red and 

 green signal lights ; and then a series of letters and articles 

 appeared in the Times drawing pubhc attention to the great 

 importance of this subject, and as a result the Board of 

 Trade inaugiu'ated compulsory tests for those engaged in 

 the Mercantile Marine as to this visual defect. There seem 

 to be three primary colour sensations which give rise to 

 all other sensations of colour — these are red, green, and 

 violet. The person who is not colour bhnd can perceive 

 with the central portion of liis retina all three of these 

 colom's. In a zone outside tliis, red is not seen ; and in a 

 zone outside of this again both red and green fail us, and 

 we can perceive only blue or violet. Colour blindness is 

 the failure of one or more of these three sensations. A 

 person may be bhnd to red, to green, to violet, or to all 

 three. The first two, however, involve each other, for a 

 person blind to red is also blind to its complementary 

 green. Blindness to violet includes blindness to yellow 

 also, but this phase of the disease is very rare indeed. It 

 must not be supposed, however, that a jjerson blind to red 

 sees green as a person possessed of normal vision does ; he 

 sees both red and green as greyish, and, in proportion as 

 he is colour bhnd, all colours containing red and green 

 will appear as if so much grey, or white and black mixed, had 

 been used in producing the colour, instead of the ordinary 

 red and green jngments. Colour-blind subjects instinctively 

 and of necessity learn to judge of the colour of light by its 

 intensity. Cases of total colour blindness, m which the 

 person is devoid of all colour perception and sees coloured 

 objects merely as shades of black and white, are exceedingly- 

 rare. 



Examinations of males and females of all races and ages 

 prove that about 3-5 of the former and 1-5 of the latter are 

 afflicted with colour blindness. 



Professor Holmgren, of Upsala, examined 32,165 men 

 and foimd 1,019 or316 per cent, colom- blind. Of 18,556 

 men tested by Dr. .Joy Jeffries, of Boston, Mass., 764 or 4-11 

 per cent, were colour blind. 



The London Committee for investigating the prevalence 



