COMPARATIVE VALUE OF VARIOUS KINDS OF STONE. 45 



It is observed by Professor Hodgkinson, in his experiments 

 on timber, that great discrepancies occurred when the woods 

 were in different degrees of dryness ; wet timber, though felled 

 for a considerable time, bearing in some instances less than 

 one-half what it bore when dry. 



Professor Hodgkinson has also experimented on round and 

 square columns of sandstone from Ped Delph, Littleborougb, 

 Lancashire, a much harder stone than that found on the 

 banks of the Aire. With regard to these experiments, it 

 appears " that there is a falling off in strength in all columns 

 from the shortest to the longest, but that the diminution is 

 so small, when the height of the column is not greater than 

 about twelve times the side of its square, that the strength 

 may be considered uniform, the mean being 10,000 lbs. per 

 square inch or upwards. 



"From the experiments on the columns lin. square, it 

 appears that when the height is fifteen times the side of the 

 square, the strength is slightly reduced ; when the height is 

 twenty-four times the height of the base, the falling off is 

 from 138 to 96 nearly; when it is thirty times the base, the 

 strength is reduced from 138 to 75 ; and when it is forty times 

 the base, the strength is reduced to 52, or to little more 

 than one-third. These numbers will be modified to some 

 extent by experiments now in progress. 



" As long columns always give way first at the ends, 

 showing that part to be ^weakest, we might economize 

 the material by making the areas of the ends greater than 

 that of the middle, increasing the strength from the middle 

 both ways towards the ends. If the areas of the ends be 

 to the area of the middle, as the strength of a short 

 column is to that of a long one, we should have for a 

 column, whose height was twenty-four times the breadth, 

 the areas of the ends and middle as 13766 to 9595 nearly. 

 . however, would make the ends somewhat too strong, 



