There is one more very important fact to know about the chronometer. It is physically impossible to keep it absolutely accurate over a long period of time. Instead of continually fussing with its adjustment and hands, the daily rate of error is ascertained, and from this the exact time for any given day. It is an invariable practice among good mariners to leave the chronometer alone. When you are in port, you can find out from a time ball or from some chronometer maker what your error is. With this in mind, you can apply the new correction from day to day. Here is an example (Put in your Note-Book):
On June 1st, CT 7h 20m 15s, CC 2m 40s fast. On June 16th, (same CT) CC 1m 30s fast. What was the corresponding G.M.T. on June 10th?
| June 1st 2m 40s fast | ||
| 16th 1m 30s fast | ||
| ———————— | ||
| 1m 10s | ||
| 60 | ||
| — | ||
| 60 | ||
| 10 | ||
| — | ||
| 15) 70s (4.6 sec. Daily Rate of error losing | ||
| June 1st-10th, 9 days times 4.6 sec. = 41 sec. losing | ||
| June 1st 2m 40s fast | ||
| June 10th 41s losing | ||
| ———— | ||
| June 10th 1m 59s fast | ||
| CT 7h 20m 15s | ||
| CC - 1 59 | ||
| —————— | ||
| G.M.T. 7h 18m 16s on June 10th | ||
| If CC is fast, subtract from CT | ||
| If CC is slow, add to CT |
WEEK III—CELESTIAL NAVIGATION
TUESDAY LECTURE
Celestial Co-ordinates, Equinoctial System, Etc.
We have already discussed the way in which the earth is divided so as to aid us in finding our position at sea, i.e., with an equator, parallels of latitude, meridians of longitude starting at the Greenwich meridian, etc. We now take up the way in which the celestial sphere is correspondingly divided and also simple explanations of some of the more important terms used in Celestial Navigation.