"Altitude or Position Line Tables." By Frederick Ball, Chaplain and Naval Instructor in His Majesty's Fleet. London: J. D. Potter. Price, fifteen shillings net per volume.
These tables have been compiled to enable navigators to find the computed true altitude and azimuth of an observed heavenly body, when working for a position point and line of position by the method of Marcq Saint-Hilaire, without the necessity of logarithmic computation. The tables appear in three volumes: one for latitudes 31° to 60° and declination 0° to 24°; one for latitudes 0° to 30° and declination 0° to 24°, and one for latitudes 24° to 60° and declination 24° to 60°; the first two are for use in all latitudes below 60° and with observations of all heavenly bodies whose declinations are less than 24°, the third extends the method to stars of high declination in high latitudes.
The tables give the altitude computed for each exact degree of latitude, declination and hour angle; hence in taking out altitudes the navigator does not use the dead reckoning position as he would if finding them by logarithmic computation, but he uses an assumed position in which the latitude is taken only to the nearest exact degree, and the longitude is such that when applied to the body's Greenwich hour angle the result will be an hour angle with an exact 4-minute interval of time. It is thus apparent that the altitude taken from the tables for this assumed position requires only correction for the odd minutes of declination, and a table (No. III) is specially provided to give this correction, the arguments in this table being the number of minutes of declination for which the correction is required and the difference of altitude for I° of declination found from the altitude table.
By a proper interchange of arguments, the azimuth may be found tabulated as hour angle in the altitude tables and converted into degrees; then having the assumed position, the observed true altitude of the heavenly body and its computed true altitude and azimuth from the tables, a position point and line of position may be found.
For all navigators who find logarithmic work laborious, these tables are recommended for their simplicity, the names of the author and his assistants being a sufficient guarantee of their accuracy.