Let me note a few misprints in Jammer’s mathematical treatment of this material. In his Eq. (15.3) on p. 273, the minus sign should be a plus sign; and on p. 275, in the treatment leading to Eq. (15.9), he uses a metric of the opposite signature to the one he used on the previous page. Also, his reference to Eq. (15.1) in the line above Eq. (15.9) should be to Eq. (15.2).