Of GREATEST ATTRACTION. 229 
Ir we fuppofe BC and BL to be equal, and therefore the 
angle BAL = the angle BAC, calling either of them 2, then 
fin @ = fin 7, by what has been already fhewn ; and from this 
equation, as 4 is fuppofed to be given, ¢ is determined. 
Tus expreflion for the attraction of an ifofceles pyramid, 
having a rectangular bafe, may be of ufe in many computations 
concerning the attraction of bodies. 
Ir the folidity of the pyramid be given, from the equations 
f=4/ 9, and fin g = fin 7’, we may determine 2, and , that is, 
the form of the pyramid when f is a maximum. 
Ler the folidity of the pyramid = m3, then , being the al- 
titude of the pyramid, and half the angle at the vertex 
ptany= half the fide of the bafe, (which is a fquare), and 
_ therefore the area of the bafe = 4 p* tan 7, and the folidity of 
the pyramid 3 p3tany ; fo that ¢ Pitan, = m3, 
Now tan 7? = ine, and fin @=fin 7’, alfo 1 — fin o= 
fin @ 
1 —fin 7 = cof’, therefore tan 77 = ———*— 
é I1—fng 
3 fo that m= 
4 p3 fin and p3 ia 3, 5 
3° ° 1—fn?’ 4 fag? he? fue 
m/f see, we have, therefore, f, that is 499 = 
9/30 Ee AP 0): This lat is; ther 
amo i/ 5 ra This laft is, therefore, a maximum 
Ef 2 by 
