532 THE POPULAR SCIENCE MONTHLY. 



as dry-rot can only thrive upon decaying timber, it is apparent that 

 the best protection against both these evils is careful seasoning. When 

 wood dries gradually in the air by the process of natural seasoning, it 

 should be placed in a dry yard and sheltered from sun and wind. 

 This method may be recommended for specimens of moderate thick- 

 ness ; and the time needed is two years for timber used in carpentry, 

 which in this period loses one fifth of its weight. Four years are 

 needed for timber that is to be used in joinery, in which time it will 

 lose one third of its weight. It is important that timber be reduced 

 to its proper size for use before seasoning ; for, however dry it may 

 become, when it is cut smaller it will shrink and lose weight. At first 

 the seasoning should proceed slowly, and the pores upon the surface 

 should remain open to permit the free evaporation of internal moisture. 

 It should be set on bearers to admit a circulation of air all around it. 

 The sleepers at the bottom of the pile should be perfectly level and 

 solid ; for timber bent in seasoning will retain the same form when 

 dried. The time required for drying under cover is shorter than in 

 the open air in the proportion of five to seven. Three years are re- 

 quired to season ship-timber ; the timbers are shaped a year before 

 they are formed, and then left a year in a skeleton shape to complete 

 the seasoning. 



Sappy timber that must be seasoned quickly, in cases where strength 

 is not chiefly required, should be immersed in running water as soon 

 as felled. It should be chained down beneath the surface, as partial 

 immersion is very destructive. Boards placed end on at the head of 

 a mill-race for two or three weeks, and then set upright in the air, and 

 turned daily, are said to floor better than timber that has been years 

 in dry seasoning. The longer wood has been under water the faster 

 it dries. The process of water-seasoning is easily explained. Sap is 

 denser than pure water, and it is inclosed in membrane. By osmotic 

 action pure water takes the place of the sap and so renders the wood 

 less liable to ferment. Again, pure water evaporates more readily 

 than water which contains certain principles in solution, and hence 

 water-soaked timber dries more rapidly. Timber steeped in water 

 has some of its substance dissolved thereby. Boiling and steaming 

 are said to prevent dry-rot by getting rid of spores and coagulating 

 albumen. 







GENEKIC IMAGES. 



By FRANCIS GALTON, F. K. S. 



IN the prescientific stage of every branch of knowledge, the preva- 

 lent notions of phenomena are mainly founded on general im- 

 pressions. But when that stage is passed, and the phenomena are 

 submitted to measurement and numbering, very many of the notions 



