[3] Inclination is the dip of the magnetic needle with a tendency to incline towards the earth. "What may that be, Uncle? Your information interests me." "Why, that the needle instead of dipping towards the pole as it does on earth, in the northern hemisphere, has an upward tendency." "This proves," I cried, "that the great point of magnetic attraction lies somewhere between the surface of the earth and the spot we have succeeded in reaching." "Exactly, my observant nephew," exclaimed my uncle, elated and delighted, "and it is quite probable that if we succeed in getting toward the polar regions--somewhere near the seventy-third degree of latitude, where Sir James Ross discovered the magnetic pole, we shall behold the needle point directly upward. We have therefore discovered by analogy, that this great centre of attraction is not situated at a very great depth." "Well," said I, rather surprised, "this discovery will astonish experimental philosophers. It was never suspected." "Science, great, mighty and in the end unerring," replied my uncle dogmatically, "science has fallen into many errors--errors which have been fortunate and useful rather than otherwise, for they have been the steppingstones to truth." After some further discussion, I turned to another matter. "Have you any idea of the depth we have reached?" "We are now," continued the Professor, "exactly thirty-five leagues--above a hundred miles--down into the interior of the earth." "So," said I, after measuring the distance on the map, "we are now beneath the Scottish Highlands, and have over our heads the lofty Grampian Hills." "You are quite right," said the Professor, laughing; "it sounds very alarming, the weight being heavy--but the vault which supports this vast mass of earth and rock is solid and safe; the mighty Architect of the Universe has constructed it of solid materials. Man, even in his highest flights of vivid and poetic imagination, never thought of such things! What are the finest arches of our bridges, what the vaulted roofs of our cathedrals, to that mighty dome above us, and beneath which floats an ocean with its storms and calms and tides!" "I admire it all as much as you can, Uncle, and have no fear that our granite sky will fall upon our heads. But now that we have discussed matters of science and discovery, what are your future intentions? Are you not thinking of getting back to the surface of our beautiful earth?" This was said more as a feeler than with any hope of success. "Go back, nephew," cried my uncle in a tone of alarm, "you are not surely thinking of anything so absurd or cowardly. No, my intention is to advance and continue our journey. We have as yet been singularly fortunate, and henceforth I hope we shall be more so." "But," said I, "how are we to cross yonder liquid plain?"