570 



SCIENCE. 



[N. S. Vol. XXII. No. 566. 



v X .005 X 2 X 110 X 80 X 108 + 



TT X .06 X 23 X 80 X 108 

 = 67,342.6 square iiini. 

 = 673.426 square cm. 



Fig. 2. The diagram to the left shows a hair- 

 let, single cell, cavity filled with air. Tlie other 

 diagram is an optical longitudinal section through 

 the diameter of a hair, showing the long, narrow, 

 thin-walled cells. These are filled with air. m, 

 cross wall; kt, hairlet; a, narrowing due to the 

 extended cell ht. This illustrates the chief means 

 of tapering of the hair, it being smaller at this 

 point by the size of the hairlet. 



Now, if this down-substance be considered 

 as a flat lamina, it would have an area of one 

 half of 673.426 sq. cm., because the lamina 

 has two sides ; and, as the lamina would be so 

 exceedingly thin, the other surfaces may be 

 neglected. Now, if t represent the thickness 

 in centimeters, a the area in sq. cm., and s the 

 specific gravity of cellulose, 



then ats = weight in grams, 

 but, by actual experiment, the weight of all 



the downs (excluding achenes) in a heac''. is 

 .0561 grams. 



thei'efore ats ■ 



.0561 

 .0561 



.0561 



336 713X1-13' 

 .0000375 



the thickness of the lamina in cm. It would, 

 therefore, require over 26,000 o± such laminae 

 to produce a thickness of one cm. 



\ 





V 



rd^.ll'0■-^■l^■<l^'>^ 



Fig. 3. Illustrates the parachute action of the 

 lamina abdc when it is horizontal and, therefore, 

 capable of producing its greatest effort. In the 

 calculation, to ^150 lbs. 



In the Standard Dictionary there are about 

 2,300 pages, having a total thickness of 11 cm., 

 something over 200 pages to the centimeter. 

 Therefore, to express in a striking manner, 

 it may be said that it would take about 130 

 of such laminae to make the thickness of one 

 leaf of the paper just mentioned. 



The weight of the achenes themselves — ex- 

 cluding the down — in a head, are approxi- 

 mately .108 gram; so that, for each gram 

 weight of achenes, there is a surface area of 

 6,235.42 square centimeters. 



' The specific gravity of cellulose in Swedish 

 filter paper is 1.13 very approximately. 



