"We sailed from Suva, in the Fijis, didn't we?" it demands, and logical mind agrees."And Suva is in east longitude?" Again logical mind agrees."And we sailed west (which would take us deeper into east longitude), didn't we? Therefore, and you can't escape it, we are in east longitude.""Greenwich time best, longitude west," chants my logical mind; "and you must grant that twenty hours and twenty-five minutes is better than eight hours and nine minutes.""All right," I break in upon the squabble; "we'll work up the sight and then we'll see."And work it up I did, only to find that my longitude was 184 degrees west.
"I told you so," snorts my logical mind.
I am dumbfounded.So is my literal mind, for several minutes.Then it enounces:
"But there is no 184 degrees west longitude, nor east longitude, nor any other longitude.The largest meridian is 180 degrees as you ought to know very well."Having got this far, literal mind collapses from the brain strain, logical mind is dumb flabbergasted; and as for me, I get a bleak and wintry look in my eyes and go around wondering whether I am sailing toward the China coast or the Gulf of Darien.
Then a thin small voice, which I do not recognize, coming from nowhere in particular in my consciousness, says:
"The total number of degrees is 360.Subtract the 184 degrees west longitude from 360 degrees, and you will get 176 degrees east longitude.""That is sheer speculation," objects literal mind; and logical mind remonstrates."There is no rule for it.""Darn the rules!" I exclaim."Ain't I here?""The thing is self-evident," I continue."184 degrees west longitude means a lapping over in east longitude of four degrees.
Besides I have been in east longitude all the time.I sailed from Fiji, and Fiji is in east longitude.Now I shall chart my position and prove it by dead reckoning."But other troubles and doubts awaited me.Here is a sample of one.
In south latitude, when the sun is in northern declination, chronometer sights may be taken early in the morning.I took mine at eight o'clock.Now, one of the necessary elements in working up such a sight is latitude.But one gets latitude at twelve o'clock, noon, by a meridian observation.It is clear that in order to work up my eight o'clock chronometer sight I must have my eight o'clock latitude.Of course, if the Snark were sailing due west at six knots per hour, for the intervening four hours her latitude would not change.But if she were sailing due south, her latitude would change to the tune of twenty-four miles.In which case a simple addition or subtraction would convert the twelve o'clock latitude into eight o'clock latitude.But suppose the Snark were sailing southwest.Then the traverse tables must be consulted.
This is the illustration.At eight A.M.I took my chronometer sight.At the same moment the distance recorded on the log was noted.At twelve M., when the sight for latitude was taken.Iagain noted the log, which showed me that since eight o'clock the Snark had run 24 miles.Her true course had been west 0.75 south.
I entered Table I, in the distance column, on the page for 0.75point courses, and stopped at 24, the number of miles run.
Opposite, in the next two columns, I found that the Snark had made 3.5 miles of southing or latitude, and that she had made 23.7 miles of westing.To find my eight o'clock' latitude was easy.I had but to subtract 3.5 miles from my noon latitude.All the elements being present, I worked up my longitude.
But this was my eight o'clock longitude.Since then, and up till noon, I had made 23.7 miles of westing.What was my noon longitude?
I followed the rule, turning to Traverse Table No.II.Entering the table, according to rule, and going through every detail, according to rule, I found the difference of longitude for the four hours to be 25 miles.I was aghast.I entered the table again, according to rule; I entered the table half a dozen times, according to rule, and every time found that my difference of longitude was 25 miles.Ileave it to you, gentle reader.Suppose you had sailed 24 miles and that you had covered 3.5 miles of latitude, then how could you have covered 25 miles of longitude? Even if you had sailed due west 24miles, and not changed your latitude, how could you have changed your longitude 25 miles? In the name of human reason, how could you cover one mile more of longitude than the total number of miles you had sailed?
It was a reputable traverse table, being none other than Bowditch's.
The rule was simple (as navigators' rules go); I had made no error.
I spent an hour over it, and at the end still faced the glaring impossibility of having sailed 24 miles, in the course of which Ichanged my latitude 3.5 miles and my longitude 25 miles.The worst of it was that there was nobody to help me out.Neither Charmian nor Martin knew as much as I knew about navigation.And all the time the Snark was rushing madly along toward Tanna, in the New Hebrides.Something had to be done.
How it came to me I know not--call it an inspiration if you will;but the thought arose in me: if southing is latitude, why isn't westing longitude? Why should I have to change westing into longitude? And then the whole beautiful situation dawned upon me.
The meridians of longitude are 60 miles (nautical) apart at the equator.At the poles they run together.Thus, if I should travel up the 180 degrees meridian of longitude until I reached the North Pole, and if the astronomer at Greenwich travelled up the 0 meridian of longitude to the North Pole, then, at the North Pole, we could shake hands with each other, though before we started for the North Pole we had been some thousands of miles apart.Again: if a degree of longitude was 60 miles wide at the equator, and if the same degree, at the point of the Pole, had no width, then somewhere between the Pole and the equator that degree would be half a mile wide, and at other places a mile wide, two miles wide, ten miles wide, thirty miles wide, ay, and sixty miles wide.
