The Gregorian epact being the age of the moon of Tebet at the beginning of the Gregorian year, it represents the day of Tebet which corresponds to January I; and thus the approximate date of Tisri I, the commencement of the Hebrew year, may be otherwise deduced by subtracting the epact from Sept.
Taking, for example, the number 1.087678, the object is to destroy the significant figure 8 in the second place of decimals; this is effected by multiplying the number by 1- 08, that is, by subtracting from the number eight times itself advanced two places, and we thus obtain 100066376.
The revenue in the Italian financial year 1905-1906 (July I, 1905 to June 30, 1906) was 102,486,108, and the expenditure 99,945,253, or, subtracting the partite di giro, 99,684,121 and 97,143,266, leaving a surplus of 2,54o,855.f The surplus was made up by contributions from every branch of the effective revenue, except the contributions and repayments from local authorities.
It is true that we obtain this result by subtracting 3 from io by means of a subtractiontable (concrete or ideal); but this table merely gives the generalized results of a number of operations of addition or subtraction performed with concrete units.
As the Syrian year began in autumn, the year of Christ corresponding to any year in the mundane era of Antioch is found by subtracting 5492 or 5493 according as the event falls between January and September or from September to January.
Dates expressed according to this era are reduced to the common era by subtracting 5502, up to the Alexandrian year 57 86 inclusive, and after that year by subtracting 5492; but if the date belongs to one of the four last months of the Christian year, we must subtract 5503 till the year 5786, and 5493 after that year.
Following the first chart of lines of equal variation compiled by Edmund Halley in 1700, charts of similar type have been published from time to time embodying recent observations and corrected for the secular change, thus providing seamen with values of the variation accurate to about 30' of arc. Possessing these data, it is easy to ascertain by observation the effects of the iron in a ship in disturbing the compass, and it will be found for the most part in every vessel that the needle is deflected from the magnetic meridian by a horizontal angle called the deviation of the compass; in some directions of the ship's head adding to the known variation of the place, in other directions subtracting from it.
Starting from the dividend, we in theory keep on subtracting the unit, and count the number of subtractions that have to be performed until nothing is left.
The year of the era, therefore, will be found by subtracting the number of the Olympic year from 776.
By subtracting the value for CH 2, which may be derived from two substances belonging to the same homologous series, from the molecular refraction of methane, CH 4, the value of hydrogen is obtained; subtracting this from CH 2, the value of carbon is determined.