“Papa explained it to me once, but I could not understand it,” replied the fair maiden.

“Then we will explain that first.  One of the great circles extending through the poles is called the prime meridian; and any one may be selected, though that of Greenwich has been almost universally adopted.  This place is near London.  From this prime meridian longitude is calculated, which means that any given locality is so many degrees east or west of it.  Sandy Hook is in longitude 74 deg., or it is that number of degrees west of Greenwich.  Aden is in 45 deg. east longitude.”

“Then you find how many miles it is by multiplying the number of degrees by 69,” suggested Miss Blanche.

“You have forgotten about knots, or sea-miles,” said Louis.

“So I have!  I should have said multiply by 60,” added the young lady.

“That would not do it any better,” replied Scott.

“Degrees of latitude are always the same for all practical purposes; but degrees of longitude are as—­

    ’Variable as the shade
  By the light quivering aspen made,’”

continued the third officer, who was about to say “as a woman’s mind;” but he concluded that it was not quite respectful to the lovely being before him.

“What a poetical sea-monster you are, Mr. Scott!” exclaimed Miss Blanche with a silvery laugh.

“I won’t do so any more,” Scott protested, and then continued his explanation.  “Degrees of longitude vary from nothing at the poles, up to 69.07 statute, or 60 geographical or sea-miles, at the equator.  We are now in about 15 deg. north latitude; and a degree of longitude is 66.65 statute miles, or 57.9855 sea-miles, near enough to call it 58.  By the way, Louis, multiply the number of statute miles by .87, and it gives you the sea-miles.  Divide the knots by the same decimal, and it gives the statute miles.”

“I will try to remember that decimal as you have done,” replied Louis.  “Now, Mr. Scott, don’t open Bowditch’s Navigator to us, or talk about projection,’ ‘logarithms,’ ‘Gunter,’ and ‘inspection;’ for I am not capable of understanding them, for my trigonometry has gone to the weeping willows.”

“Talk to us in English, Mr. Scott,” laughed Miss Blanche.

“Let us go up to Conference Hall, where there is a table,” said the third officer, as he produced a book he had brought up from his state-room.  He led the way to the promenade, where he spread out a chart in the “Orient Guide,” which had twenty-six diagrams of a clock, one at the foot of every fifteen degrees of longitude.  At this point the commander came upon the promenade.

“Formerly the figures on a timepiece in Italy, and perhaps elsewhere, went up to twenty-four, instead of repeating the numbers up to twelve; and these diagrams are constructed on that plan,” continued Scott.

“An attempt has been made to re-establish this method in our own country.  I learned once from a folder that a certain steamer would leave Detroit at half-past twenty-two; meaning half-past ten.  But the plan was soon abandoned,” interposed the captain.