284 APPENDIX. 



The power gained in the wheel and axle is as the radius 

 of the wheel to that of the axle. 



The power gained by an inclined plane is as the length 

 to the height. 



The power of the wedge is generally as the length to 

 the thickness of the back. 



The power of the screw is as the circumference to the 

 distance of the thread, or as 6.2832 to that distance. 



Resistance is an affair of experiment, sometimes a third, 

 and at other times less. 



The friction of cylinders or wheels is as the pressure, 

 and inversely as the diameter. 



The least friction is when polished iron moves on brass. 



The area of a circle is the product of the diameter and 

 circumference, divided by 4. 



A fall of one tenth of an inch per mile, will produce a 

 motion in rivers. The greatest velocity is at the surface 

 and in the middle, and the least at the bottom and sides. 

 But as the velocity increases, the action on the sides and 

 bottom increases also. 



Eclipses return in the very same order every 18 years 

 and 1 1 days, supposing four leap years in the interval, and 

 if five, then every 10 days. Other cycles of motion, how- 

 ever, vary the phenomenon or measure. The moon's shad- 

 ow is less than 170 miles broad ; but the eclipse, in de- 

 gree, for 2,000 miles. 



A pump ten feet above a well, with seven inches bore, 

 will discharge 70 gallons a minute ; and at 30 feet 4 inches, 

 23 gallons. 



The specific gravity of water being 1.000, that of al- 

 cohol, pure, is 0.829 ; beer, 1.034 ; cider, 1.018 ; milk, 

 1.032; linseed oil, 0.94; vinegar, 1.025; sea-water, 

 1.026; ox bone, 1.666; brass, 7.824; brick, 2.; cork, 

 0.24; gold, 19.2587; granite, 2.728 ; bar iron, 7.68; lead, 

 11.352; lignum-vitse, 1.33; mahogany, 1.06; marble, 

 2.716 ; mercury, 13.58 ; oak, 1.17 ; platina, 20.722 ; sil- 

 ver, 10.474; clay-slate, 2.67; tin, 10.717, limestone, 

 1.386 ; elm, 0.671 ; honey, 1.45. — Treasury of Knowledge. 



MEASURES OF LENGTH. 



Measures of length are the distance of one object from 

 another, accordinjr to some agreed standard. 



A line is the twelfth of an inch, and the 144th of a foot. 



