Table of contents

An instrument is described in which the momentum of single cosmic-ray particles is measured, the particles leaving the instrument in a sufficiently collimated beam for use in subsequent experiments. The `maximum detectable momentum' of the apparatus is about 3 × 10¹⁰ eV/c., almost all particles are collected within 10° of the zenith and in directions individually defined to ±1°, the output is about 400 particles/day, and the proportion of spurious records is of the order of, or less than, 0.1%.

The paper describes the electronic selection and recording systems of the spectrograph and the performance and overall serviceability of the equipment as shown in continuous operation over about one year.

Penetrating showers have been investigated, using Geiger counters, at a depth of 30 m. below ground, at sea level and at an altitude of 3,457 m. The influence of the geometry of the absorbers was studied. The transition curves for local showers, corrected for this geometric effect, give the following collision lengths of the generating particles: Pb, 180±40; Al, 85±15; Paraffin similar 80 gm/cm². These values correspond to a collision cross section close to the geometric cross section of the nuclei. From the results obtained for extensive penetrating showers, it is concluded that most of the penetrating particles in these showers appear to be generated in the atmosphere. In 40 days, no penetrating showers were recorded below ground. Using photographic plates, the density distribution of shower tracks associated with nuclear disintegrations was found to be similar at sea level and 3,457 m.

Using the method of ` delayed coincidences ' measurements have been made at sea level on the flux of slow mesons travelling backwards from the ground.

The second moments of the electron-photon cascades are evaluated. It is found that the mean square fluctuation at the cascade maximum is that expected for a Poisson distribution or less; before and after the maximum the fluctuation exceeds greatly that expected for a Poisson distribution. The correlation coefficient between electrons and photons is zero for small thicknesses or near the cascade maximum. For other regions the correlation coefficient is positive. Both mean square fluctuation and correlation between electrons and photons can be understood qualitatively in terms of fluctuation of effective depth.

The cross section for the scattering of electrons by atomic nuclei is investigated at energies for which the nuclei can no longer be treated as point charges. Two simple nuclear models are used. A general expression is obtained using Born's approximation, and an exact numerical calculation is carried through for 20 MeV. electrons scattered by gold nuclei. It is concluded that at this energy considerable deviations from the formulac which treat the nucleus as a point charge should be expected, and that these should furnish some information about the charge distribution within the nucleus.

An approximate linear form of the Peierls-McManus equations of motion for an electron is shown to yield runaway solutions for a particular influence function, which otherwise satisfies all the conditions imposed by the theory. The general problem is to discuss the existence of complex roots of a transcendental equation for an arbitrary form of the influence function. It is shown that this equation always has roots. These, however, may be such that the corresponding motion of the free electron is of a damped nature. It has not been found possible to construct a function which avoids runaway solutions or to prove whether or not such a function exists when all conditions are satisfied.

The band-spectrum of BaO between 5000 and 7000 Å., which consists of a single ¹Σ - ¹Σ system, has been the subject of a new rotational analysis in which the following bands have been examined: 5,0, 4,0, 3,0, 3,1, 2,0, 2,1, 1,1, 1,2, 0,2, 0,3 and 0,4. The constants derived are:

Bν'' = 0.31249 - 0.00130(ν'' + ½) - 0.00002(ν'' + ½)2	Bν' = 0.2584 - 0.00111(ν' + ½)
D'' = 26.5 × 10-8	D' = 28 × 10-8
re'' = 1.940 × 10-8 cm.	re' = 2.133 × 10-8 cm.
ωe'' = 669.81, xe''ωe'' = 2.054	ωe' ~ 500, x'ωe' = 1.6
ν0, 0 = 16722.25 cm-1.

In the upper state some 16 perturbations have been found. They appear to arise from interactions with at least four electronic states or substates. Fairly complete information about one of the perturbing levels has been obtained. The constants of this state are: Bν = 0.2254 - 0.0013₅(ν + ½), Gν = 450.₄(ν + ½) - 2.₉(ν + ½)², ν_{0, 0} =17476.₇ cm^-1.

The band-constants of the other perturbing states are very similar to those given above.

The spectrum of ZrO has been photographed in the ultra-violet, the visible and the infra-red, from arcs running under special conditions. This has made possible the identification of three new systems in the ultra-violet, as well as two less conspicuous ones in the infra-red. It has also made it possible to extend the blue system α of ZrO.