Descrlptlve units To the Editor: Strobel ( I ) and Wadlineer (2) discuss the use of "descriptive units'; i'n connectionkith periodic motion and suggest that T should have units attached to it. The foUowiug comments may further help clarify this matter. In mathematics the quantity 0 in expressions like sin0 stands for the numerical value? of a n angle measured in radians. The reason why 0 is treated as a number is seen in de Moivre's theorem: exp(i0) = cos0 i sin0. For B to be used in an expression like exp(i0) clearly 0 has to be a number. The matter bv traditional inconsistencies in - - - ~ - - is com~licated notation and definition. ~ h uangle i is often defined by angle = arclradius. More exactlv. anele = (ardradius) radian. The ratio arclradius measures on& the numerical value of the anele in radian. Another inconsistencv in this area is the use of an expression like sin 30"; it is expressions like these that lead us to think that 0 must bean ande. O is certainly related to an angle, but it is not an angle. 1f0 is to be treated as an anele, notational consistency would require us to write sin (8i;ad) or sin[i9/(l80/n)deg) snd erp(iblrad). Expresxions like cos Z r u t are notationally consistent since ut is number and so is T, but an expression like cos(2svt 6 ) would be notationally consistent only if 6 is regarded as the numerical value of the phase angle in radians. If w is in rad s-I, an expression like cos (wt) should be more properly written as cos (wtlrad). Whatever the merits of Wadlinaer and Strobel's s"ggesti'ons about the descriptive units to-be attached to ?r, it seemsvery likely that the scientific community will continue the use of the present notation, inconsistent though it may be, for quite some time. Indeed, chemistry abounds in inconsistent notation. For example, we often treat the eauilibrium constant as a quantity with units but continue td use expressions like AGO =
