PREFACE TO THE SECOND EDITION 



IN addition to a thorough revision, Lessons VI. and 

 XXIV. have been largely re-written. Figs. 9, 10, 52, 60, 

 64, and 66 are new, and Figs. 9, 10, n, 64, 66, and 67 of 

 the first edition have been withdrawn. 



I have received valuable help from Professors W. N. 

 Parker and G. B. Howes, Miss M. Greenwood, and 

 Mr. J. E. S. Moore. Much of the proof-correcting has, 

 as before, fallen upon my brother. 



March 1893. 



