have laughed at as the absurd fancies of an unbalanced mind. The lesson to be learnt from the practical aviation of the present day is that of the triumph of principle over precedent, of the working out of an idea to its logical conclusions in spite of the accumulated testimony of all past experience to the contrary; and with such a notable example before us can we say that it is futile to enquire whether by the same method we may not unlock still more important secrets and gain some knowledge of the unseen causes which are at the back of external and visible conditions, and then by bringing these unseen causes into a better order make practical working realities of possibilities which at present seem but fantastic dreams? It is at least worth while taking a preliminary canter over the course, and this is all that this little volume professes to attempt; yet this may be sufficient to show the lay of the ground.

Now the first thing in any investigation is to have some idea of what you are looking for — to have at least some notion of the general direction in which to go — just as you would not go up a tree to find fish though you would for birds’ eggs. Well, the general direction in