PREFACE ix 



me the use of a number of figures which have done duty in other 

 books of mine. My thanks are also due to Mr. Murray, who 

 has encouraged me in a work which I was often tempted to 

 abandon, whose good-humoured patience over many delays I 

 should long since have exhausted had he been as many men 

 are. 



J. A. T, 



The University of Aberdeen, 

 August 1907. 



