254 OBSERVATIONS 



Thus, let PA and D E (T. 2. fig. 4.) be two parallel lines, 

 and let A B and A G reprefent two ftraight mufcles, and 

 AD and AE two oblique mufcles, it is plain, that when the 

 two ftraight mufcles have fhortened themfelves one third part 

 of their length, their infertion A will be brought down to num- 

 ber 1. But when the oblique mufcles A D and AE, by acting 

 together, have brought the point A down to 1, and are in the 

 fituation of the dotted lines iD and iE, they cannot have loft 

 more of their length than the length of the perpendicular Ai, 

 which is fhorter than the hypotenufe AZ>, or lefs than the third 

 of the length of the oblique mufcle. In fact, they have loft 

 lefs of their length than At, becaufe the two fides Ai and iE 

 of the triangle AiE muft be longer than the third fide AE; 

 and therefore oblique mufcles can perform as great a degree of 

 motion as ftraight mufcles, without being fhortened in the fame 

 proportion ; or, which is the fame thing, if they continue to 

 act till they are fhortened in the fame proportion, the place of 

 their infertion, A, will defcend farther, or through a larger 

 fpace. 



I shall now proceed a flep farther, and endeavour to de- 

 monftrate, that where two oblique mufcles balance each other, 

 the motion of their infertion is more extenfive than can be pro- 

 duced by two ftraight mufcles of the fame length with the 

 oblique mufcles. 



Thus, in T. 2. fig. 5. let A B and A C reprefent two ftraight 

 mufcles, and A D and A E two oblique mufcles of the fame 

 length, and we fhall fuppofe the length of each mufcle to |con- 

 fift of any given number of inches or parts, fuppofe five parts, 



I, 2, 3, &c. or I, II, III, &c. and when in action to be capa- 

 ble of fhortening itfelf one fifth part or two fifth parts of its 

 length. Let the two correfponding numbers 1 and I, or 2 and 



II, be joined by the ftraight lines 1 I, and 2 II, fo as to form 

 the ifofceles triangles Ail, or A 2 II. When the two ftraight 



mufcles 



