P L A 



PIPES, leaden and iron,, weight of. (Gregory.) 



Let I be the length in feet, d the interior diameter, and t the thickness 

 both in inches and parts of an inch, W the weight in hundred weights j 

 then, 



In a leaden pipe, W = ,1382 It (d + f.) 



In a cast iron pipe, W = ,0876 lt(d+t.) 



PIPES for conveying Water. See Fluids t pressure of. 



PLANE inclined. See Inclined Plane. 



PLANETS, Elements, 8fc. of. 



What are usually called the elements of a planet's orbit are in number 

 seven. 



1. The longitude of the ascending node of the orbit. 



2. The inclination of the orbit to the plane of the Ecliptic. 



3. The mean motion of the planet round the sun. 



4. The mean distance of the planet from the sun. 



5. The eccentricity of the orbit. 



6. The longitude of the aphelion. 



7. The epoch at which the planet is in the aphelion. 



Elements and general view of the Planetary System. ( Laplace t 

 Maskelyne, Fince, Play fair.} 



205 



