In 1935 van der Corput, in connection with his work on distribution functions, was led to the following conjecture which expresses the fact that no sequence can, in a certain sense, be too evenly distributed.

That these two subjects—the History of Science and the Psychology of Invention—are intimately connected with one another, is immediately evident and needs no explanation. Perhaps, however, it has not always been sufficiently appreciated. The recent Congress for the History of Science (Jerusalem, 1953) has given me an opportunity of trying to apply to the latter the data of the former.

Among Schubert's many experiments in the application of a symbolic calculus to problems of enumerative geometry, some special attention is due to his long memoir entitled “Anzahlgeometrische Behandlung des Dreiecks” [1]. For one thing, he is dealing here with a simple, though not elementary, kind of geometric variable, the triangle in a fixed plane, so that the paper gives a clear insight into his general method; and, for another, there is contained in this paper, as was recently suggested by Freudenthal ([2], p. 19), an apparently miraculous device, the introduction of “infinitesimal triangles”, which we can now recognize (§4) as having had the effect of desingularizing the triangle domain in which the calculus was to operate. The principal target of Schubert's investigations was the discovery of Bézout-type formulae for the number of triangles common to two algebraic systems Σr and Σ6-r (r = 1, 2, 3) of complementary dimensions, the systems being supposed to intersect in only a finite number of triangles, and the multiplicities of these triangles being assumed to be suitably defined. His systems, also, had to be “normal” i.e. they could only contain such sub-systems of degenerate triangles as were of the dimensions he regarded as normal. He found, by his methods, that “normal” system Σ1 and Σ5 are each characterized (in so far as intersection numbers are concerned) by 7 projective characters, systems Σ2 and Σ4 by 17 such characters, and systems Σ3 by 22 such characters.

This functional equation for Dedekind's

has been established in many different ways; however, it seems that the following proof, a straightforward application of the theorem of residues, has not been observed before. Since

it suffices to prove that

As is well known the stability of viscous flow between two concentric rotating cylinders was first successfully treated both experimentally and theoretically by G. I. Taylor [1]. The mathematical problem underlying this classical investigation in hydrodynamic stability is the following:

The hydrodynamical equations allow the stationary solution

for the rotational velocity at a distance r from the axis of rotation, where A and B are constants related to the angular velocities Ω1 and Ω2 with which the inner and outer cylinders (of radii R1 and R2, R2 > R1) are rotated. Thus

where

Graham Higman (1) has investigated quasi-order [(2), p. 4] relations a ≤ b on a set S which, in his terminology, have the following finite basis property:

If A ⊂ S, then there is a finite set B ⊂ A such that, given any a α A, there is some b α B satisfying b ≤ a.

Let q(x1; …, xn) be a positive definite quadratic form in n variables with real coefficients. Minkowski defined the successive minima of q as follows. Let S1 denote the least value assumed by q for integers x1 …, xn, not all zero, and let be a point at which this value is attained. Let S2 denote the least value assumed by q at integral points which are not multiples of x(1), and let x(2) be such a point at which this value is attained. Let S3 be the least value of q at integral points which are not linearly dependent on x(1) and x(2), and so on. We have

and it is easy to see that these numbers are uniquely defined, even though there may be several choices for the points x(1), …, x(n). The determinant N of the coordinates of the points x(1), …, x(n) is a non-zero integer. We denote by N (q) the least value of this integer (taken positively) for all permissible choices of the n minimal points, and by N′(q) its greatest value. Plainly N(q) and N′(q) are arithmetical invariants of q, that is, they are the same for two forms which are equivalent under a linear substitution with integral coefficients and determinant ±1.

The object of this paper is to solve the Saint-Venant torsion problem for those cross-sections with inclusions, which are such that the z-plane boundaries involved can be mapped into concentric circles in a complex ζ-plane by the transformation

with z´(ζ) ≠ 0 or ∞ within the cross-section. We shall consider both solid and hollow inclusions having different elastic rigidities μ. In the case of the solid inclusion we have to restrict the coefficients as to be zero for all negative s, but it is an advantage to leave this restriction to the end of the analysis, since the forms of certain coefficients in the two cases differ only in this respect.

Let f = f(x, y, z) be a positive definite form of the type

where x, y, z are integral valued variables, and the coefficients a, …, t are integers whose highest common factor is 1. As the determinant of such a form may be fractional, I define

and

thus — C is the discriminant of the binary form f(x, y, 0), and the necessary and sufficient condition for f to be positive definite is that a > 0, C > 0, and d > 0.

In §§2, 3 a simple expression in finite terms is found for the small transverse displacement of a thin plane elastic plate due to a transverse force applied at an arbitrary point of the plate. The plate is clamped along, and is bounded internally by, the parabola CDE shown in Fig. 1.

The following theorem is typical of a group of results which have been found to be of importance in the theory of Cesàro summability.

Theorem A. If 0 ≤ ρ ≤ κ (κ, ρ integer), p > −1,p+q −1 and

and ifsn = 0(np) (C, κ), thensn εn = 0(np+q) (C, ρ).

Minkowski's fundamental theorem and the Minkowski-Hlawka theorem play basic complementary roles in the Geometry of Numbers. Blichfeldt showed essentially that Minkowski's fundamental theorem was a simple consequence of a more general theorem, in which the convex body was replaced by any measurable set and the lattice was replaced by a discrete set of points having a definite asymptotic density. Hlawka himself showed that the Minkowski-Hlawka theorem could be proved in a slightly modified form, when the star body was replaced by any measurable set, but he did not replace the lattice by a more general set of points.

Stokes's stream-function for an axisymmetrical irrotational motion of perfect incompressible liquid, bounded by a plane [1], or by a sphere [2], has been expressed in terms of the stream-function for the motion in an unbounded liquid. Corresponding results are found in this note for the slow steady motion of a viscous liquid, when the motion in unbounded liquid is irrotational.

The problem of the stability of a fluid rotating about an axis to an axisymmetric disturbance has been examined in the inviscid case by Rayleigh [1], who derived a simple criterion based on an analogy with the stability of plane stratified fluid of variable density. Later a complete discussion of the stability of viscous motion between rotating cylinders for small axisymmetric disturbances was given by G. I. Taylor [2]. More recently, the problem of magneto-hydrodynamic stability has claimed the attention of several workers, and, amongst other problems, the stability of a rotating fluid, when a constant magnetic field is applied in the direction of the axis of rotation, has been examined by Chandrasekhar [3]

It is well known that every irrational number θ possesses an infinity of rational approximations p/q satisfying

It is also well known that there is a wide class of irrational numbers which admit of no approximations which are essentially better, namely those θ whose continued fractions have bounded partial quotients. For any such θ there is a positive number c such that all rational approximations satisfy

The general features of the interaction of hydrodynamic and electromagnetic effects, when an electrically conducting fluid medium is in motion in the presence of a magnetic field, are now well established. A discussion of these effects in which the equations of the system are set out and an analogy is drawn between the behaviour of the magnetic field and that of vorticity in a viscous fluid, is given by Batchelor [1]. The development of the subject may be divided broadly into two sections. First, there are the problems of engineering interest, such as flow of conducting fluid in pipes, with associated problems of stability, and secondly there are the problems of astrophysical and geophysical interest.

A method of assessing the accuracy of an approximation to the steady two-dimensional flow of viscous incompressible liquid past a flat plate is developed. The approximate solution, with stream-function ψ1 is closely related to the boundary-layer solution, and is expressed in terms of the function used in that theory. The conditions at the surface of the plate and at infinity are exactly satisfied by ψ1 but the equation of (finite) motion is not exactly satisfied. However, ψ1 is an exact solution of a problem in fluid motion, if a body force, of appropriate magnitude depending on ψ1 is assumed to act on the fluid. The magnitude of this force provides a criterion of the accuracy of ψ1, and some use has been made [5] of this means of estimating accuracy. This criterion is, in effect, only qualitative, since it is not possible to make a numerical estimate of the effect on the motion of a body force which is non-conservative and acts over the whole field of flow.