FLUENTS, OR INTEGRALS.
SECTION I. Definitions.—II. General Theorems.—III. Rational Fluxions.—IV. Irrational Fluxions.—V. Circular Fluxions.—VI. Logarithmic Fluxions.—VII. Exponential Fluxions.—VIII. Index of Fluxions.
SECT. I.—Definitions.
THE fluents of such expressions, as are the most likely to occur in the solution of physical problems, may be very conveniently arranged in the form of a TABLE; the principal materials of which will be extracted from Meier Hirsch's Integraltafeln. 4. Berlin, 1810. It might have been somewhat enlarged by additional matter that may be found in the earlier publications of our countrymen Waring and Landen, which have been particularly consulted on the occasion; but Waring's improvements relate most commonly to cases so complicated, as seldom to be applicable to practical purposes; and Landen's theorems, though incomparably more distinct and better arranged than Waring's, tend rather to the investigation of some elegant analogies, than to the facilitation of actual computations. Some of these, however, will be briefly noticed, and an improvement in the mode of notation will be attempted, which, if universally adopted, would tend to save much unnecessary circumlocution in the enunciation of many general theorems.
1. The earlier letters of the alphabet, as far as q, and sometimes r, are commonly employed to denote constant quantities; the subsequent letters generally for quantities considered as variable. They are here employed as relating indifferently to quantities positive or negative, and to numbers whole or fractional; except when they are used as indices or exponents.
2. The Italic character is employed, in preference to others, for denoting quantities in general, the Roman for characteristic marks, as d for a fluxion, or differential, sin, cos, or f, ϕ, for sine and cosine; and
hl for hyperbolic logarithm. The long Italic , however, not being otherwise used, serves very conveniently as a characteristic, to denote a fluent.
3. When the Italic letters m, n, p, q, r, or any others, are employed as indices, they are to be here understood as denoting any numbers without limitation; the Roman small letters, m, n, will be applied to whole numbers only, excluding fractions, but either positive or negative, or 0; the small Italic Capitals M, N, to positive numbers, whether whole or fractional, excluding negative numbers only; and the small Roman Capitals M, N, to positive integers only, including however 0.
4. The characteristic implies the sum of a finite number of terms, derived from all the possible variations of a quantity, which is here denoted by a small letter of the Greek alphabet.
5. A comma, in an index, denotes or.
6. The fluents, indicated by the table, are to be understood as corresponding equally to any particular values of the quantities concerned; so that, in order to obtain the expression of the definite quantity required by the conditions of any problem, we must always take the difference of the two values found by substituting two values of the elementary variable quantities; and this rule being general, it supersedes the necessity of introducing a constant correction of the fluent in each particular case.
7. Particular values of fluents, limited on both sides, are distinguished by accents, .
SECT. II.—General Theorems.
Exception. In the case , the theorem fails, and we must substitute
x being the initial value of y, this theorem gives the increment of y corresponding to any increment of x beginning at the same time: it may be called the master key which opens a way to all the treasures of analysis. From Taylor, Meth. Incr.
SECT. III.—Rational Fluxions.
Examples.
Examples.
Put , .
Fluents. 88.
89.
E.
a. , an odd number; putting ,
, values.
90.
; the characteristic implying the sum of the values depending on those of . From Cotes's discoveries.
91. ; 1, when is negative, putting ; ; relating to the values of
; 2, when is positive, putting ;
; relating to the values of
F.
92. ; first, being , and
putting and ,
;
; secondly, being , and putting ,
G.
93.
94.
95.
96.
97.
98.
H.
99. ; being successively each of the roots of the equation , and ; provided, however, that the denominator contain higher powers of than the numerator, and that all the values of be different; a limitation first laid down by Newton.
100.
101.
. The ambiguity of the roots being decided by the conditions of the problem.
Remark. In some of these cases, the signs of the roots, being ambiguous, require to be determined by the conditions of the problem; but we must adhere to the same root in the same solution.
Particular values, from to ; putting .
Particular values, from to ; putting .
Fluents. 212.
Particular values, from to ; putting .
i.
ii.
iii.
iv.
v.
vi.
m.
213.
214.
215.
E.
a.
216. ; thus
217.
218.
219.
b.
220.
221.
222.
c.
223.
224.
225.
226.
d.
227.
228.
229.
e.
230.
231.
232.
233.
f.
234.
235.
236.
(A): thus
Particular values, from to .
Relation of particular values, from to
Particular value, from to
SECTION V.—Circular Fluxions.
It may be remarked that
; continuing the series through all positive angles, and putting instead of .
We have for the powers of , ; + when , - when
; and
,
+ when , and - when ; the
last term, when it becomes , being altered
to .
c.
c.
f.
g.
D.
E.
405.
hl tang
406.
f.
a.
407.
408.
409.
410.
411.
412.
b.
413.
414.
415.
416.
417.
418.
c.
419.
420.
421.
422.
tang
423.
424.
d.
425.
426.
427.
428.
429.
430.
e.
431.
432.
tang
433.
434.
tang
435.
436.
f.
G.
a.
b.
c.
Fluents.
hl
d.
e.
f.
H.
a.
b.
c.
d.
e.
N. .
I. ,
K. ,
L. ,
M. . For all values of .
O. .
P.
or, for
Q.
R. . For fractional powers see Méc. Cél.; also Ivory and Wallace, Ed. Trans. 1798, 1805.
SECT. VI.—Logarithmic Fluxions.
A.
B.
Since (n5), taking the of this theorem = , and , we have
When is a negative whole number = , we may obtain a finite series by making , and , but the last term still contains a fluent.
Particular values, from to .
SECT. VII.—Exponential Fluxions.
A.
In the theorem
we may put either , , and , or , , and ; and, in the former manner, we obtain,
Fluents. 560.
561.
562.
563.
564.
565.
566.
567. ; making
568.
Particular value, from to
569.
Putting, in the Taylorian theorem,
(n.5) , , and , we have,
570.
Particular value, from to
571. , Laplace, Méc. Cél. X.; or thus,
, , , ; ; , and
(n.554): in this expression we may make , then , and if we wish to have ,
we must take , and will be , so that the series will give us
; but these series will fail in the extreme cases, although they converge with sufficient rapidity in most others.
Putting , we have and taking , and , we obtain the series.
572.
573.
574.
575.
G.
H.
I.
SECT. VIII.—Index of Fluxions.
- 1.
- 2.
- 3.
- 4.
- 5.
- 6.
- 7.
- 30.
- 51.
- 72.
- 90.
- 92.
- 93.
- 99.
- 102.
- 144.
- 172.
- 216.
- 258.
- 300.
- 301.
Transformations. For