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tioned. Thus, after what has been done, it would be proper, first of all, to calculate the hyperbolic logarithm of 11, then that of 13, &c.
Proceeding according to the method already explained, it will be found that The hyperbolic logarithm of 11 is 2.397895273016
of 13 is 2.564999357538 of 17 is 2.833213344878
of 19 is 2.944438979941 Logarithms were invented by Lord Neper, Baron of Merchiston in Scotland. In the year 1614, he published at Edinburgh a small quarto, containing tables of them, of the hyperbolic kind, and an account of their construction and use. The discovery afforded the highest pleasure to mathematicians, as they were fully sensible of the very great utility of logarithms; but it was soon suggested by Mr. Briggs, afterwards Savilian Professor of Geometry in Oxford, that another kind of logarithms would be more convenient, for general purposes, than the hyperbolic. That one set of logarithms may be obtained from another will readily appear from the following article.
14. It appears from articles 1, 3, and 7, that if all the logarithms of the geometrical progression 1, 1+a', 1+a)', 1+a', 1+a+, 1+a', &c. be multiplied or divided by any given number, the products and also the quotients will likewise be logarithms, for their addition or subtraction will answer to the multiplication or division of the terms in the geometrical progression to which they belong. The same terms in the geometrical progression may therefore be represented with different sets or kinds of logarithms in the following manner: 1, 1+ a)', 1+a?, 1+ a), 1 + a)", 1+a", 1+a", &c. 1, 1+a', 1+a)", 1+a", 1+a“, 1+a", 1+a", &c. 1, 1+ a", 17. a", 1+ am, I +a", 1+ a", i+a", &c.
In these expressions 1 and m denote any numbers, whole or fractional; and the positive value of the term in the geometrical progression, under the same number in the index, is understood to be the same in each of the three series. Thus if i ta' be equal to 7, then 1+a" is equal to 7, as is also 1 + a j. If i+albe equal to 10, then 1+a)" is equal to 10, as is also 1 +a", &c. If
therefore 1, 21, 31, &c. be hyperbolic logarithms, calculated by the methods already explained, the logarithms expressed by
1 2,3, &c. may be derived from them; for the hyperbolic logarithm of any given number is to the logarithm in the last-mentioned set, of the same
1 number, in a given ratio. Thus 41 : 4 ::1:
4lm Im; 6 also 61 :
6lm Im 15. Mr. Briggs's suggestion, above alluded to, was that I should be put for the logarithm of 10, and consequently 2 for the logarithm of 100, 3 for the logarithm of 1000, &c. This proposed alteration appears to have met with the full approbation of Lord Neper; and Mr. Briggs afterwards, with incredible labour and perseverance, calculated extensive tables of logarithms of this new kind, which are now called common logarithms. If the expeditious methods for calculating hyperbolic logarithms explained in the foregoing articles *, had been known to Mr. Briggs, his trouble would have been comparatively trivial with that which he must have experienced in his operations.
16. It has been already determined that the hyper bolic logarithm of 5 is 1.6094379127, and that of 2 is 0.69314718054, and therefore the sum of these logarithms, viz. 2.30258509324 is the hyperbolic logarithm of 10. If, therefore, for the sake of illustration, as in article 14, we suppose 1+a)' = 10, and allow, in addi
2 3 4 tion to the hypothesis there formed, that &c. denote common logarithms, then bl=2.30258509324, and = 1; and the ratio for reducing the hyperbolic logarithm of any number to the common logarithm of the same number, is that of 2.30258509324 to 1. Thus in order to find the common logarithm of 2, 2.30258509324 :1::0.69314718054 : 0.3010299956, the common logarithm of 2. The common logarithms of 10 and 2 being known, we obtain the common logarithm of 5, by subtracting the coinmon logarithm of 2
* Some of the principal particulars of the foregoing methods were discovered by the celebrated Thomas Simpson. See also Mr. Hellin's Mathematical Essays published in 1788.
from 1, the common logarithm of 10; for 10 being divided by 2, the quotient is 5. Hence the common logarithm of 5 is 0.6989700044. Again, to find the common logarithm of 3, 2.30258509324:1:: 1.0986122 8864 : 0.4771212546 the common logarithm of 3.
17. As the constant ratio, for the reduction of hyperbolic to common logarithms, is that of 2.30258509324 to 1, it is evident that the reduction may be made by multiplying the hyperbolic logarithm, of the number whose common logarithm is sought, by
Thus 1.9459 1014899, the hyperbolic logarithm of 7, being multiplied by .4342944818, the product, viz. .8450980373, &c. is the common logarithm of 7.
The common logarithms of prime numbers being derived from the hyperbolic, the common logarithms of other numbers may be obtained from those so derived, merely by addition or subtraction. For addition of logarithms, in any set or kind, answers to the multiplication of the natural numbers to which they belong, and consequently subtraction of logarithms to the division of the natural numbers. Hyperbolic logarithms are not only useful as a medium through which common logarithms may be obtained: they are absolutely necessary for finding the fluents of many fluxional expressions of the highest importance.
It is deemed unnecessary in this place to show the utility of logarithms by examples. Being once calculated and arranged in tables, not only for common numbers, but also for natural sines, tangents, and secants, it is manifest that a computer may save himself much time, and a great deal of labour, by means of their assistance; as otherwise multiplications and divisions of high numbers, or of decimals to a considerable number of places, would enter into his inquiries.
The writer of the foregoing articles now considers the design with which he set out as completed. He has endeavoured to explain, with perspicuity, the first principles of logarithms, and their relations to one another when of different sets or kinds; and he has laid before the young mathematical student the most improved and expeditious methods by which they may be calculated. If the reader should be desirous of further information on the subject, he may meet with full gratification by the perusal of the history of discoveries and writings relating to logarithms, prefixed to Dr. Hutton's Mathematical Tables. He will also find the Tables of Logarithms, contained in that volume, the most useful for calculation, if in his computations he does not go beyond degrees and minutes : if he aims at a higher degree of accuracy, he will have recourse to Taylor's Tables, in which the Logarithmic Sines and Tangents are calculated to every second of the Quadrant.
I. The pole of a circle of the sphere is a point in the
superficies of the sphere, from which all straight lines drawn to the circumference of the circle are equal.
II. A great circle of the sphere is any whose plane passes
through the centre of the sphere, and whose centre therefore is the same with that of the sphere.
III. A spherical triangle is a figure upon the superficies of
a sphere comprehended by three arches of three great circles, each of which is less than a semicircle.
A spherical angle is that which on the superficies of a
sphere is contained by two arches of great circles, and is the same with the inclination of the planes of these great circles.
PROP. I. Great circles bisect one another. As they have a common centre, their common section will be a diameter of each which will bisect them.
PROP. II. Fig. 'I. The arch of a great circle betwixt the pole and the circumference of another is a quadrant.
Let ABC be a great circle, and D its pole: if a great circle_ DC pass through D, and meet ABC in C, the arch DC will be a quadrant.
Let the great circle CD meet ABC again in A, and let AC be the common section of the great circles, which will pass through E, the centre of the sphere: join DE, DA, DC: by def. 1. DA, DC are equal, and AE, EC are also equal, and DE is common; there