iv 



PREFACE. 



Great then indeed must be my anxiety on 

 the present occasion, when I am rash enough to 

 deviate another time from the Spanish line of 

 certitude, into the mazes of chance and danger ; 

 where the track which I am to pursue is ill 

 defined and flinty, and may possibly lead me 

 and my new little book into some quagmire or 

 other ; there to perish without assistance ; the 

 scorn of the critics, and the pity of disappointed 

 friends. However, be this as it may, my die is 

 cast, my steam is on, and I am already at the 

 opposite bank of the Rubicon. 



The volume which I now present to an in- 

 dulgent public, is an unsolicited donation to the 

 widow of my poor departed friend Mr. Loudon, 

 whose vast labours in the cause of Science 

 have insured to him an imperishable reputation. 

 If this trifling present on my part shall be the 

 medium of conveying one single drop of balm 

 to the wound, which it has pleased Heaven 

 lately to inflict on the heart of that excellent 

 lady, my time will have been well employed, 

 and my endeavours amply requited. 



