X PREFACE. 



although at the eleventh hour, to fulfil our engagement 

 to our pupils and to the public. 



To our friend Dr. H. Hyde Salter we are indebted for 

 several excellent drawings, as well as for other valuable 

 assistance. 



We desire also to express our thanks to Mr. Vasey 

 for the skill and ability with which he has executed his 

 portion of the task, that of engraving the drawings on 

 wood. 



W.B. R.B.T. 



LONDON, 



December 1st, 1856. 



