228 report— 1859. 



1854 the quantity of cotton manufactured goods exported was only 39,000,000 

 yards, and in 1858 it rose to 728,000,000 yards. The total value of our exports of 

 cotton stuffs and yams to India in 1858 was £10,249,826. Machinery has been 

 exported to India since 1855 to the extent of half a million annually. 



On the Statistics of Colour- Blindness. By Professor George Wilson, M.D. 

 The object of this communication was to urge the importance of an extended 

 inquiry into the prevalence of colour-blindness. The number of persons markedly 

 Qolour-blind was, according to 



Dalton (1st determination) , . 12 per cent. 



Dalton (2nd determination) , , , 8 „ 



Pierre Prevost , 5 „ 



Seebeck , , 12 „ 



Kelland 2 „ 



Q. Wilson 1-8 say 2. 



In a recent Report to the Royal Society, Sir John Herschel has expressed his sur- 

 prise at the high per-centage obtained by the author, which appeared to him incom- 

 patible with the apparent rarity of colour-blindness among his own circle of acquaint- 

 ances. Dr. Wilson's figures, however, are the lowest which have been given, and 

 they were obtained by the examination of 1154 persons, the largest number which 

 has hitherto been examined in reference to their vision of colour. How far the 

 per-centage thus obtained represented the condition of the entire community, it was 

 impossible to decide. That colour-blindness, nevertheless, was far from being very 

 rare, and that its comparative abundance had, in relation to workers in coloiu's and 

 to railway and naval coloured signals, an important bearing on many professions, 

 and on the welfare of the entire community, the author illustrated by many exam- 

 ples, ending by asking the assistance of the Section in collecting its statistics. 



MECHANICAL SCIENCE. 



On the Rivers " Dee" forming the Ports of Aberdeen and Chester. 

 By J. Abernetiiy, C.E. 



On Coal-pit Accidents. By Captain J. Addison. 

 The author proposes to detect the presence of the explosive gas in coal mines by 

 the use of balloons filled with hydrogen ; and carbonic acid gas, or "choke damp," 

 by the use of balloons filled with common air. These, when introduced into a mine, 

 would at once show the force of gravity, the nature and extent of the gaseous accu- 

 mulation; ventilation might then be accomplished by the introduction of copper 

 cylinders filled with compressed atmospheric air, which could be liberated, and thus 

 expel the noxious gases. 



On an Improved Method of maintaining a True Liquid Level, particularly 

 applicable to Wet Gas-Meters. By Alexander Allan. 



The author proceeded to explain the working of a model and drawings illustrating 

 his method of measuring the consumption of gas, and explained that, whereas by the 

 present law an error ranging up to 5 per cent, was legalized, by the plan proposed, 

 tried under severe tests, and in actual operation with gas passing through in a con- 

 siderably greater quantity than the size was calculated for, the result was that the 

 maximum per-centage of error amounted to only one-fourth per cent., a result 

 hitherto unequalled. 



On a Safety Cage for Miners. By Robert Aytoun. 

 To cause the cage, on the failure of the winding tackle, to cling to the guide-rods 



