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heels to port in the Northern hemisphere, the N. end of the compass needle being attracted to the highest side of the ship; the magnet A, with its North end uppermost, repels the North end of the compass needle and attracts the South end, and brings the compass to its proper position.
Fig. 5 shows the effect of the heel to port in the Southern hemisphere; the South end of the needle is drawn to the highest side, and the South end of the magnet A is uppermost to counteract the attraction.
QUESTIONS ON THE LAW OF STORMS.
FOR MASTERS, FIRST AND ONLY MATES.
The Candidate is to answer in writing the whole of these questions, num. bering his answers with numbers corresponding with the questions.
state the probable bearing of the centre in
2. And suppose the wind during the passage of the same
Cyclone were found to change towards the
Cyclone, and what action would you take ? 3. Under what conditions would the change in the direc
tion of the wind in the Cyclone be the reverse of
the above ? 4. What are the usual indications of a ship being on the
line of progression of the centre of a Cyclone ?
* The Examiners will fill in these blanks.
What are the usual indications that a ship is (a) ap
proaching the centre of a Cyclone, and (6)
receding from it ?
ANSWERS TO THE FOREGOING QUESTIONS. 1. Note.—The answer to this question is found by ap
plying the following rule:
Rule.—For Northern Hemisphere. Take eight points to the right of the direction of the wind.
For the Southern Hemisphere. Take eight points to the left of the direction of the wind.
Example.—In the N. Hemisphere suppose the wind is East, take eight points to the right of East, and we get South for the bearing of the
centre. 2. If the wind changes to the right.—The ship is on the
right hand side of the line of progression. Either shape a course away from the centre of
the storm, or heave to on the starboard tack. If the wind changes to the left.—The ship is on the left
hand side of the line of progression. Either shape a course away from the centre of the storm, or heave to on the port tack.
3. The change in the direction of the wind would be
the reverse to that given in question No. 2 if the ship and the storm were travelling in the same direction, but the ship going faster than the storm. The change would also be the reverse if the ship were on the other side of the line of
progression, but not going faster than the storm. The Barometer falling rapidly, the wind and sea in
creasing, but the wind not shifting. 5. (a) The Barometer falling, wind and sea increasing,
and the wind shifting more rapidly. (b) The Barometer rising, wind and sea moderating,
and the wind steadies. 6. North Atlantic.—They commence generally in lat. 8°
to 20°, travelling to the WNW. and NW, and when in about 30° to the N, NE, and ENE, gradually increasing in diameter, but somewhat less violent as they progress, until they become expended and break up, occurring most frequently in the months of July, August, September, and October.
Bay of Bengal. Westerly to NorthWesterly during the months of May, June, October, November, and December.
China Seas.-Westerly to North-Westerly in July and August, and South-Westerly to North-Westerly in the months of September, October, and November.
Indian Ocean.-They commence generally in lat. 8° to 20°, travelling to the WSW and SW, and when in about 30° to the S, SE, and ESE, gradually increasing in diameter, but somewhat less violent as they progress, until they become expended and break up, occurring most frequently in the months of January, February,
March, and April. For further information on the Law of Storms you are referred to page 110 of “ Newton's Seamanship Examiner.”
LOGARITHMS are a series of numbers by which we are enabled to perform the process of Multiplication and of Division by the ordinary rules of Addition and Subtraction.
The INDEX to the Log of a number is one less than the number of figures to the left hand of the decimal point.
3 The Log of any number consisting of four figures or less can be taken from the Table of Logs at sight. If the number consists of more than four figures a correction is required for the extra figures, unless they are cyphers, when no correction is required. Thus the Log of 7894000. is 6.897297 the same as the Log of 7894.
The Log of 2708 is 432649 Tab. Diff. 160
+7 Multiplied by 046
From 7360 cut off the three right-hand figures and 7 remains, which is to be added to the Log 432649. Then supply the Index by the above rule, and the required Log is found to be 4.432656.
EXAMPLE. Required the Log of 333.515.
3335 is 523096 Cor. for 15
Tab. Dif. 130
EXAMPLES FOR PRACTICE.
60009.05 For Answers, see end of book.
To find the log of a fractional or decimal number.--For the Index; subtract the number of cyphers (which follow the decimal point) from 9, and the remainder is the required index. Thus the index to the
Log of .0469 is 8.
.000469 6. The other portion of the log is found in the usual way, that for each of the above numbers is the of Log 469. Find the Logs of the following numbers :.96
.965 .0965 .0096532 .00096532
.8500065 For Answers, see end of book.
TO FIND THE NUMBER CORRESPONDING TO A GIVEN Log.-If the Index does not require more than four figures, the required number can be taken from the Table of Logs at sight. But if the Index requires more than four figures, and the given Log cannot be found in the Tables, then take out the next lesser Log to that given; subtract the Log taken out from the given Log. To the right of the remainder place one cypher and divide this number by the Tab. Diff. Add another cypher to the remainder, and divide again. Continue until the number of figures more than four required by the Index is found.