Source on Isaac Barrow

“[R]ecent work... removes him from a major role in the development of the calculus or in Newton's early mathematical thinking. ...[T]he new symbolic algebra... was essential to calculus. Barrow accepted neither the art nor the notion, and... avoided the technique wherever possible. The theorems in the Geometrical Lectures that historians juxtapose to form the fundamental theorem of calculus belong to... different lines of inquiry, one... characterized by its freedom from... "tediousness of calculation" and divorced in Barrow's mind from... infinitesimals or limits. The central lectures contain a program of research, but... not... the program that led Newton and Leibniz to the calculus.”

“Michael Sean Mahoney, "Barrow's Mathematics: between ancients and moderns" Before Newton: the Life and Times of Isaac Barrow (1990) ed., Mordechai Feingold.”

“'''''Isaac Barrow was the first inventor of the Infinitesimal Calculus; Newton got the main idea of it from Barrow by personal communication; and Leibniz also was in some measure indebted to Barrow’s work''', obtaining confirmation of his own original ideas, and suggestions for their further development, from the copy of Barrow’s book that he purchased in 1673.''”

“By the "Infinitesimal Calculus," I intend "a complete set of standard forms for both the differential and integral sections of the subject, together with rules for their combination, such as for a product, a quotient, or a power of a function; and also a recognition and demonstration of the fact that differentiation and integration are inverse operations."”

“Barrow was familiar with the paraboliforms, and tangents and areas connected with them, in from 1655 to 1660 at the very latest; hence he could... differentiate and integrate by his own method any rational positive power of a variable, and thus also a sum of such powers.”

“He further developed... [infinitesimal calculus] in the years 1662-3-4, and in the latter year probably had it fairly complete. In this year he communicated to Newton the great secret of his geometrical constructions... and it was probably this that set Newton to... attempt to express everything as a sum of powers of the variable.”

“During the next year Newton began to "reflect on his method of fluxions," and actually did produce his Analysis per Æquationes. This, though composed in 1666, was not published until 1711.”

“Leibniz bought a copy of Barrow’s work in 1673, and was able "to communicate a candid account of his calculus to Newton" in 1677. In... the face of Leibniz’ persistent denial that he received any assistance whatever from Barrow’s book... bear... in mind Leibniz’ twofold idea of the "calculus":— (i) the freeing of the matter from geometry, (ii) the adoption of a convenient notation. ...[O]n these two points ...he derived not the slightest assistance from Barrow’s work; for the first ...would be dead against Barrow’s practice and instinct, and of the second Barrow had no knowledge whatever. ...[F]or [these points] ...the world has to thank Leibniz; but their inception does not mean the invention of the infinitesimal calculus. This, the epitome of the work of his predecessors, and its completion by his own discoveries until it formed a perfected method of dealing with the problems of tangents and areas for any curve in general, i.e. ...the differentiation and integration of any function whatever (such as were known in Barrow’s time), must be ascribed to Barrow.”

“My attention was arrested by a theorem in which Barrow... rectified the cycloid, which... has usually been ascribed to Sir C. Wren. ...What I found induced me to treat a number of the theorems ...I came to the conclusion that Barrow had got the calculus; but I queried even then whether Barrow himself recognized the fact.”

“Only on completing my annotation of the last chapter of this volume, Lect. XII, App. III, did I come to the conclusion that is given as the opening sentence of this Preface; for I then found that a batch of theorems.., on careful revision, turned out to be the few missing standard forms, necessary for completing the set for integration; and that one of his problems was a practical rule for finding the area under any curve, such as would not yield to the theoretical rules he had given, under the guise of an "inverse-tangent" problem.”

“[T]he conclusion is the effect of a gradual accumulation of evidence... I have given a wholly inadequate account of the work of Barrow’s immediate predecessors; but... to a sufficiency for... showing... the time was... ripe for the work of Barrow, Newton, and Leibniz.”

“I have to all intents rewritten Barrow’s book; although throughout I... adhered... to Barrows own words. I have only retained those parts which seemed... essential for the purpose in hand. This was necessary... that room might be found for... critical notes on the theorems.., proofs omitted by Barrow, which when given in Barrow’s style, and afterwards translated into analysis, had an important bearing on the point as to how he found out the more difficult of his constructions; and lastly for deductions therefrom that point steadily, one after the other, to the fact that Barrow was writing a calculus and knew that he was inventing a great thing.”

“I have used three distinct kinds of type: the most widely spaced type has been used for Barrow’s own words; only very occasionally have I inserted anything of my own in this, and then it will be found enclosed in heavy square brackets, that the reader will have no chance of confusing my explanations with the text... Barrow makes use of parentheses very frequently, so that the reader must understand that only remarks in heavy square brackets are mine... The small type is used for footnotes only. In the notes I... use the Leibniz notation, because it will... convey my meaning better; but there was really no absolute necessity for this, Barrow’s a and e, or its modern equivalent, h and k, would have done quite as well.”

“The beginnings of the Infinitesimal Calculus... arose from determinations of areas and volumes, and the finding of tangents to plane curves. The ancients attacked the problems in a strictly geometrical manner, making use of the "method of exhaustions." ... This was the method by means of which Archimedes proved most of his discoveries. But there seems to have been some distrust of the method, for we find... many... discoveries... proved by a reductio ad absurdum...”

“Galileo... would appear to have led the way, by the introduction of the theory of composition of motions into mechanics; he also was one of the first to use infinitesimals in geometry, and from... what is equivalent to "virtual velocities" it is... inferred that the idea of time as the independent variable is due to him. Kepler... was the first to introduce... infinity into geometry and to note that the increment of a variable was evanescent for values of the variable in the immediate neighbourhood of a maximum or minimum; in 1613, an abundant vintage drew his attention to the defective methods in use for estimating the cubical contents of vessels, and his essay on the subject (Nova Stereometria Doliorum) entitles him to rank amongst those who made the discovery of the infinitesimal calculus possible.”

“In 1635 Cavalieri published a theory of "indivisibles," in which he considered a line as made up of an infinite number of points, a superficies as composed of a succession of lines, and a solid as a succession of superficies, thus laying the foundation for the "aggregations" of Barrow. Roberval seems... first, or... an independent, inventor of the method; but he lost credit... because he did not publish it, preferring to keep the method... for his own use... a usual thing... of that time, due perhaps to... professional jealousy. The method was severely criticized... especially by Guldin, but Pascal... showed that the method of indivisibles was as rigorous as... exhaustions... they were practically identical. ...[T]he progress... is much indebted to this defence by Pascal. Since this method is... analogous to... integration, Cavalieri and Roberval have... claim... as... inventors of... one branch of the calculus; if it were not for the fact that they only applied it to special cases, and seem... unable to generalize... owing to cumbrous algebraical notation, or to have failed to perceive the inner meaning... concealed under a geometrical form. Pascal... applied the method with great success, but also to special cases only; such as his work on the cycloid.”

“The next step was... more analytical... [B]y the method of indivisibles, Wallis... reduced... many areas and volumes to... the series (0^m + 1^m + 2^m +... n^m) / (n + 1)n^m, i.e. the ratio of the mean of all the terms to the last term, for integral values of n; and later he extended his method, by a theory of interpolation, to fractional values of n. Thus the idea of the Integral Calculus was in a fairly advanced stage in the days immediately antecedent to Barrow.”

“What Cavalieri and Roberval did for the integral calculus, Descartes... accomplished for the differential branch by his... application of algebra to geometry. Cartesian coordinates made possible the extension of... drawing... tangents to... curves of any kind. ...[H]e habitually used the index notation ...this had a very great deal to do with ...Newton's discovery of the general binomial expansion and of many other infinite series. Descartes failed, however, to make... great progress... in... drawing of tangents, owing to... an unfortunate choice of a definition for a tangent to a curve in general. Euclid's circle-tangent definition being more or less hopeless in the general case, Descartes had the choice of three:—  (1) a secant, of which the points of intersection with the curve became coincident (2) a prolongation of an element of the curve... considered as composed of an infinite succession of infinitesimal straight lines; (3) the direction of the resultant motion, by which the curve might have been described. Descartes chose the first. ...I cannot see that it would have been possible for a Descartes to miss the differential triangle and all its consequences if he had chosen the second definition. ... Descartes... in his rule for the tangents to roulettes... considers a curve as the ultimate form of a polygon. The third definition, if not originally due to Galileo, was a direct consequence of his conception of the composition of motions; this definition was used by Roberval... and applied successfully to a dozen or so... well-known curves; in it we have the germ of the method of "fluxions." Thus... Roberval occupies an almost unique position, in that he took a great part in the work preparatory to the invention of both branches of... calculus...”

“Fermat... adopted Kepler's notion of the increment of the variable becoming evanescent near a maximum or minimum value, and upon it based his method of drawing tangents. Fermat's method of finding the maximum or minimum... involved the differentiation of any explicit algebraic function, in the form that appears in any beginner's text book of today (though Fermat does not seem to have the "function" idea); that is, the maximum or minimum values of f(x) are the roots of f'(x) = 0, where f'(x) is the limiting value of [f(x+h) - f(x)]/h; only Fermat uses the letter e or E instead of h.”

“Here then we have all the essentials for the calculus; but only for explicit integral algebraic functions, needing the binomial expansion of Newton, or a general method of rationalization which did not impose too great algebraic difficulties, for their further development; also, on the authority of Poisson, Fermat is placed out of court, in that he also only applied his method to certain special cases. Following the lead of Roberval, Newton subsequently used the third definition of a tangent, and the idea of time as the independent variable, although this was only to insure that one at least of his working variables should increase uniformly. This uniform increase of the independent variable would seem to have been usual for mathematicians of the period and to have persisted for some time; for later we find with Leibniz and the Bernoullis that d(dy/dx) = (d2y/dx2)dx. Barrow also used time as the independent variable in order that, like Newton, he might insure that one of his variables, a moving point or line or superficies, should proceed uniformly; ...Barrow... chose his own definition of a tangent, the second of those given above; and to this choice is due in great measure his advance over his predecessors. For his areas and volumes he followed the idea of Cavalieri and Roberval.”

“Thus we see that in the time of Barrow, Newton, and Leibniz the ground had been surveyed, and in many directions levelled; all the material was at hand, and it only wanted the master mind to "finish the job." This was possible in two directions, by geometry or by analysis; each method wanted a master mind of a totally different type, and the men were forthcoming. For geometry, Barrow; for analysis, Newton, and Leibniz with his inspiration in the matter of the application of the simple and convenient notation of his calculus of finite differences to infinitesimals and to geometry. With all due honour to these three mathematical giants, however, I venture to assert that their discoveries would have been well-nigh impossible... if they had lived a hundred years earlier; with the possible exception of Barrow, who, being a geometer, was more dependent on the ancients and less on the moderns of his time than were the two analysts, they would have been sadly hampered but for the preliminary work of Descartes and the others I have mentioned (and some I have not—such as Oughtred), but especially Descartes.”