In a highly interesting critical account of the mathematical work of James Gregory (1638–1675), written for the Proceedings of the Edinburgh Mathematical Society, (1) 41 (1923), 2–25, by the late Professor G. A. Gibson, there occurs at p. 8 something of a mathematical puzzle. On that page a pair of formulae are quoted, which certainly are striking examples of the analytical power of Gregory, and which run as follows:—

Gibson adds that “there is another formula (Rigaud, p. 207), but it is of a very complicated character and I do not reproduce it.” It will be convenient to refer to the above pair as formulae A′ and B′, and to the more complicated but analogous series as formula C, and to the original series, from which the above were transcribed, as formulse A and B. I am indebted to Mr A. Inglis for drawing my attention to the problem.

Absolute summability according to Cesàro's method has been defined by Fekete for positive integral orders, as follows:—

Denoting the rth partial sum of a series Σun by and its rth mean, namely2, by we can regard as the sum of the series

.

In a paper entitled “Sets of anticommuting matrices” Eddington proved that if El, E2, …., Eqform a set of q four-rowed square matrices satisfying the relations,

,

where E is the unit matrix, then the maximum value of q is five. Later Newman showed that this result is a particular case of the general theorem that ifE1, E2, …., Eqform a set of q t-rowed square matrices satisfying (1), where t = 2Pτ and τ is odd, then the maximum value of q is 2p + 1.

The present paper describes briefly a notation for representing continued fractions in many dimensions, which has the advantage providing a direct method of attack and of rendering intuitive, results which are usually proved by induction. The notation is the outcome of a generalisation which I previously made [1] in connection with the solution of certain difference equations. Only formal theorems are considered here. For a discussion of convergence reference may be made to the works [2, 3, 4, 5] cited at the end. The paper by Paley and XJrsell is particularly important since these authors discuss very fully the non-cyclic simple continued fraction

One of the many interesting problems discussed by Ramanujan is concerned with the effect of truncating at its maximum term nn/n! the exponential series for en, where n is a positive integer. When n is large, the sum of the first n terms is, roughly speaking, half the sum of the whole series.

There are various methods in existence for the practical solution of a set of simultaneous equations

Some of these methods are appropriate to special systems, as for example to the axisymmetric “normal equations” of Least Squares. In many applications, however, as in problems of statistical correlation of many variables, it may be desired not merely to solve a given set of equations but to obtain as much knowledge as possible about the system or matrix of coefficients; perhaps to evaluate its determinant and various minors, such as principal minors, possibly also to determine the elements of the adjugate matrix, or the reciprocal matrix. The examination of the sign of successive principal minors of an axisymmetric determinant, in order to find the signature of the corresponding quadratic form, is a case in point; and there are many such applications.

A lemma used in the above paper can be extended to cover the case of a sequence Sn determined by a recurrence relation of the form

r being any positive integer.

For convenience denote everywhere. Let us suppose that an inequality of the form

holds for p = 2, 3, … ., n — 1. The constant K can be determined from the initial values of Sn, when kn and ln have been found.

In der Theorie der Invarianten binärer Formen gilt der Satz, dass die projektiven Komitanten eines vollen Systems durch sukzessives Ueberschieben berechnet werden können. Hierauf beruht der Originalbeweis für die Endlichkeit, den. P. Gordan 1868 zuerst gegeben hat. Konstruktiv wird dieser Beweis aber erst dann, wenn man von vorneherein eine obere Grenze für den Grad der Komitanten eines vollen Systems in den Koeffizienten der Grundformen angeben kann. Also eine natürliche Zahl N, die die Sicherheit gibt, dass alle Komitanten eines vollen Systems gefunden sind, wenn man die Ueberschiebungen soweit berechnet hat, dass ihr Grad N nicht übersteigt.