(4) 4)13 + (P23 + 033 30)10203 = 1. The addition formulae and other properties have been given in recent times by Silberstein [1], Oniga [2] and Bruwier [3], [4], while Mikusinski [5], [6] and Poli [7], [8] have studied the corresponding third order circular functions. Earlier workers in this field were Appell [9], Glaisher [10] and Villarceau [11]. It is the object of this note to show that the solution of a special type of Abel's nonlinear differential equation of the first kind ([12], [13], [14]), viz., dy = fo(x) + fi(X)y + f2(X)y2 + f3(x)y3 dx X)3 can be expressed explicitly in terms of combinations of 4)-functions and the