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X-ray scattering from single crystals of the di-n-alkyl ethers of pentadecaethylene glycol with n = 13, 15 and 16 was consistent, for all practical purposes, with an orthorhombic unit cell including 4 molecules with space group Pcca. The long spacing varied with chain length but the other unit cell dimensions were common to all three samples. Powder photographs from a wider range of pentadecaethylene glycol di-n-alkyl ethers, n = 13 to 18 inclusive, were indexed by means of the orthorhombic unit cell with average values of a = 9.38 A and c = 9.11 A . Scattering from the samples orientated by directional crystallisation was also indexed and the rotational axes identified.

The justification of discounting in project appraisal is often given as the diminishing marginal utility of increasing per capita GNP. However, rates of individual income growth vary greatly between project beneficiaries, implying different group discount rates. Use of average rates of income growth can seriously distort calculated present values of projects, particularly those of long duration.

The application of Kula's sum of discounted consumption flows method to forestry investment gives a more favourable result than NPV, but leads to some curious consequences. In particular, the immediate future generation may not be provided with a timber resource by the present generation, while being expected to provide such a resource for its own successors. The method does not in fact treat future generations equitably: downward revision of the social discount rate, possibly to zero, is a better means of achieving this objective.

The potential applications of chemical intensification in dental radiography are explored. Three standard photographic intensifiers and three methods designed for radiographic use are evaluated. One of these methods is shown to be capable of reducing radiation dose to one half, without loss of diagnostic quality. Further work is necessary to achieve a system sufficiently practicable to deserve widespread use in routine clinical dental radiography.

A lithium polystyrene carboxylate was synthesized with a number-average molecular weight of 576 ± 46 g mol−1. The synthesis involved adding lithium polystyryl (prepared anionically using sec-butyl lithium as initiator) in a toluene/tetrahydrofuran mixture to a saturated solution of carbon dioxide in a similar solvent mixture. Molecular motion in globular particles formed by the association of the lithium polystyrene carboxylate in water was studied by 300 MHz 1H and 75.5 MHz 13C NMR over a temperature range of 10°–120°C. Longitudinal relaxation times (T1) were measured using the (π-τ-π/2) inversion recovery sequence, whilst apparent transverse relaxation times ( T 2 ∗ ) were obtained from line-widths at half height. An interesting feature of the system is that the segmental and diffusional motions are sufficiently hindered to allow the overall tumbling of the particles to strongly influence the relaxation processes. From T2 data at 23°C, it is estimated that the colloidal particles have a radius of 6 nm, which compares favourably with a solid radius of 5.7 nm determined by electron microscopy. The size of the colloidal particles suggests that some ion pairs are trapped in the cores.

Poly(oxyethylene) n-alkyl ethers of formula CH3(OCH2CH2)m O(CH2)nH, where m has number-average values of 27 or 53 and n has unique values in the range 12 to 30, have been investigated with regard to the behavior of their aqueous micellar solutions in size-exclusion chromatography (SEC) on Sepharose 4B gel. Semiquantitative agreement is found between the experimental SEC curves and the behavior predicted by Coll's equations. The results can be used to show that the micellar aggregation numbers are large (⩾100) and that the micellar size distributions are narrow.

The thermodynamics of micelle formation by a polystyrene-b-polyisoprene block copolymer in n-hexadecane, which is a selectively bad solvent for polystyrene, has been investigated. The temperature dependence of the critical micelle concentration (c.m.c.) was determined from measurements of scattering intensity against temperature carried out at seven concentrations within the range (1.24–3.25) × 10−4 mol dm−3. A plot of 1n (c.m.c.) against T−1 gave a value for the standard enthalpy of micellisation of −40.7 ± 2.2 kJ mol−1 of copolymer chains. The standard entropy contribution ( −TΔS ⊖ ) to the standard free energy of micellisation was found to be positive. The results are in strong contrast to those reported for synthetic surfactants in aqueous media below 50°C for which a favourable standard entropy change is the factor mainly responsible for micelle formation.

A study was made of stereocomplex formation by a mixture of isotactic and syndiotactic samples of poly(methyl methacrylate) in tetrahydrofuran. Specimens were isolated from solution at various times and examined by electron microscopy after first evaporating off the solvent. Initially, globular particles were found; later, branched fibrillar stuctures were observed. Finally, the stereocomplex particles started to form microgel. The structural development which was observed to occur explains the apparently diverse results of some earlier studies.

In the uncertainty that surrounds the future availability of nonrenewable natural resources and the efficacy of technological advance, the economic costing of resources should be undertaken probabilistically. While optimistic assumptions entail little change from the costing procedures used in conventional cost-benefit analysis, even moderately pessimistic assumptions lead to a much increased cost for nonrenewable resources. These lead in turn to a reappraisal of the value of investment and of the cost ascribed to other factors of production. Even when optimistic assumptions are deemed the more plausible, a utility-maximizing evaluation may still give more emphasis to pessimism.

Aqueous size-exclusion chromatography was used to determine hydrodynamic volumes of micelles formed by four series of poly(oxyethyelene) methyl-n-alkyl ethers, CH3(OCH2CH2_mO(CH2)nH, with m having number-average values in the range 13–53 and n having values in the range 12–21. The surfactants in solution were injected at concentrations far above their critical micelle concentrations in order to avoid complexities due to the micelle-free-chain equilibrium. The hydrodynamic volumes of the micelles were found to increase with increase in n at fixed m and also with increase in m at fixed n. The effects of block lengths m and n on the aggregation numbers of the micelles was roughly estimated by combining their hydrodynamic volumes with measures of their intrinsic viscosities.

Lamella spacings, specific volumes and melting points have been determined for a series of well characterized poly(ethylene oxide)/poly(propylene oxide) type PEP block copolymers with E-block length 48 chain units and P-block lengths 0 to 7 chain units. These properties are interpreted in terms of a stacked lamella model with alternating amorphous and crystalline layers. Both extended-chain and once-folded-chain crystalline lamellae are found, the former with thickness about 32 E chain units and the latter with thickness about 21 E chain units. Compared with the specific volume of supercooled melt of the same composition the specific volume of the polymer in the amorphous lamellae is lower in the extended-chain polycrystals and higher in the once-folded-chain polycrystals. The melting points of the copolymers are low compared to that of perfectly crystalline poly(ethylene oxide), i.e. 37 to 55°C compared with T 0 m = 76°C. This is due to the large positive free energy of formation from the melt of the crystalline/amorphous end interface ( σ o ) and the amorphous layer ( σ a ). For extended-chain polycrystals we find σ o ∼ 3 kJ/mol and σ a ∼ 3.5 kJ/mol; for once-folded-chain polycrystals we find σ o ∼ 6 kJ/mol and σ a ∼ 2 kJ/mol. We also find σ o , x = 2.5 kJ/mol for a completely extended-chain end interface and σ o , f = 10 kJ/mol for a completely folded-chain end interface.

The crystallization of two fractions of poly(ethylene oxide), with molecular weights of 6000 and 360 000, has been studied by simultaneous dilatometry and calorimetry. The crystallization isotherms obtained by the two techniques are identical for the low molecular weight fraction, but differ for the high molecular weight fraction.

Overuse of recreation sites seems to justify regulation, and the principal tools for this are fee charging or physical exclusion. Both seem equally costly to administer. Both involve equal costs to consumers if recreationists visit from one origin, but if they come from different origins, costs may be greater and consumers' surplus less under either tool, depending on the shape of the demand curve. Which is the more equitable tool depends on the relative representation of rich and poor participants from near and distant origins. Potentially beneficial use of site revenues is an advantage of charging. Neither availability of substitutes nor variation in daily demand seems likely to change these results substantially, but a system of booking admissions before the trip outset might neutralize the advantages of charging. The optimal level of use varies with the regulatory tool chosen. The optimal admissions under exclusion could be fewer than or more than under charging, or may even be equal to unregulated use.

The profitability of forestry depends on the future trend of timber prices. Three plausible price predictions placed the margin of profitability at three widely differing levels of physical productivity. A good estimate of the elevation at which marginal profitability could be expected under each price prediction was given by productivity/elevation regressions for existing plantations in each of three localities in North Wales. Cartographic sampling enabled the cumulative area of rough grazings below this elevation to be estimated. By combining empirical relationships between price trend, profitability, productivity, elevation and cumulative area, a heavy dependence of afforestable area on future price trend can be demonstrated for North Wales; similar results would be expected throughout Britain. Inclusion of land products other than timber complicates the exercise. The significance of price trend for many forestry decisions justifies much more research on price prediction.

A sensitometric method was used to compare the effects of changing kilovoltage and filtration on the sensitivity of a dental radiographic emulsion. Five combinations were investigated: 90 kVp, 3.5 mm. aluminum filtration; 90 kVp, 2.5 mm. Al; 70 kVp, 2.5 mm. Al; 70 kVp, 1.5 mm. Al; and 50 kVp, 1.5 mm. Al. Maximum emulsion sensitivity was demonstrated at 90 kVp and 3.5 mm.aluminum filtration; 90 kVp, 2.5 mm. Al and 70 kVp, 2.5 mm. Al showed slight reductions in sensitivity (4 percent and 6 percent, respectively). A progressively greater reduction in emulsion sensitivity was observed at 70 kVp, 1.5 mm. Al (10 percent) and 50 kVp, 1.5 mm. Al (26 percent). Emulsion sensitivity is one factor to be considered when one is selecting beam quality.

In cost-benefit analysis, natural resources, like other factors of production, should be costed as a mixture of marginal social cost of exploiting additional resources and lost marginal social benefit of forgone alternative uses, according to the way in which extra resources are made available to a project. For a nonrenewable resource, changes in future marginal social cost and marginal social benefit are likely to add significantly to the immediate elements of cost, as successively less tractable resource stocks are exploited. Of the several reasons given for ignoring these future costs, the most plausible is that technological advance justifies a heavy discount on the future. However, neither historical nor logical arguments demonstrate the inevitability of efficacious technological advance.

The occupation of residential space imposes externalities on those travelling from the outer margin of that space to the city centre. The free market price does match the social cost under many models of city structure, and so promotes optimal occupation of space, provided that all journeys are to and from the centre. If additionally there are journeys to the countryside for recreation, the free market understates social cost at the periphery. Public land ownership to provide social services may cause the free market price to exceed the social cost near the centre. The implication that planned densities should be less variable than those generated by the free market is generally supported by other social and economic arguments.

A convenient route was established for synthesizing a polystyrene-b-poly(ethylene oxide) block copolymer. Polystyryl lithium, prepared by initiating the polymerization of styrene with sec-butyl lithium, was end-capped by reaction with ethylene oxide. After isolation and characterization, the product was reacted with potassium methoxide to give a polymeric anion with a potassium counterion. The system was then used to initiate the polymerization of ethylene oxide to form the second block. Micellar aggregates formed by the polystyrene-b-poly(ethylene oxide) block copolymer in water were investigated by transmission electron microscopy using a phosphotungstic acid stain for the polyether component. Two types of colloidal particle differing greatly in average size were shown to be present in solution.

Social cost-benefit analysis generally ignores the changes induced in markets which interact with a project, on grounds that the changes are small. A simulation model of interaction shows that this is not generally so; when distortion, maldistribution and factor inertia exist, cost-benefit analysis will normally produce a seriously incorrect evaluation of the overall utility change resulting from a project.

Intrinsic viscosity and light scattering data are reported for fractions of the poly(styrene oxide) and for fractions of a commercial sample of poly(ethylene oxide). A few results obtained for fractions of the poly( t -butyl ethylene oxide) are also included. The following intrinsic viscosity/molecular weight relationships are obtained: [η] ( benzene at 25°C )=3.97×10 −4 M 0.686 v [η] ( toluence at 25°C )=6.79×10 −5 M 0.766 v Estimates of the unperturbed dimensions of these polymers yield values of ( r 2 0 M ) 1 2 of 0·93 A for poly(ethylene oxide) and of 0·64 A for poly(styrene oxide).

Samples of natural rubber were vulcanized in the presence of n-decane, decalin and o-chlorobenzene. The diluents were then removed, and the force-extension characteristics of the samples studied over the range 1.1

The Treasury's use of 10 per cent as a discount rate in its recent cost-benefit study of forestry has important implications for land use. A discount rate derived from the market rate of return on investment, or from political choice, tends consistently and irrationally to undervalue future consumption. The only rational function of a discount rate is to relate mean predicted value of a future product to the present value of a similar product. From trends of prices and marginal utility of money, and from economic and political predictions, different rates appropriate to different products could be calculated. The rates of land-based products are likely to be low, and such rates alter the presently-ascribed absolute and relative values of different land uses. Resume DU CHOIX JUDICIEUX DES ELEMENTS ET DU DANGER DES CRITERES IRRATIONNELS DANS LES CONJECTURES ECONOMIQUES: LE TAUX D'ESCOMPTE NATIONAL ET SES IMPLICATIONS DANS L'UTILISATION DES SOLS L'emploi par le Tresor d'un taux d'escompte de 10 pour cent, dans sa recente etude des couts et rendements de la sylviculture, a des effets implicites importants pour l'utilisation des sols. La decision d'assimiler le taux d'escompte au taux de remuneration des investissements sur le marche appelle des doutes du point de vue rationnel, et un taux d'escompte fonde sur le jeu du marche ou sur un choix politique tend uniformement et irrationnellement a sous-estimer la consommation future. Un taux d'escompte devrait faire la relation entre la valeur moyenne prevue d'un produit futur et la valeur presente du meme produit. En predisant les tendances des prix et l'utilite marginale de l'argent et en etablissant la differentiation des effets divers de l'incertitude, il est possible de calculer des taux differents pour des produits differents. Les taux afferents aux produits derives du sol sont susceptibles d'etre faibles, et ces taux modifient les valeurs absolue et relative a present attribuees aux differentes utilisations des sols. Zusammenfassung IN DIE ZUKUNFT: MIT GLEICHGULTIGKEIT ODER SORGE? Der Gebrauch eines Diskontsatzes von 10 Prozent in den letzten forstwirtschaftlichen Kosten-Nutzen-Studien durch das Finanzministerium beinhaltet wichtige Folgerungen fur den Gebrauch von Land. Die vernunftgemasse Erklarung, den Diskontsatz durch den Marktertragssatz fur Investitionen auszudrucken, ist zweifelhaft, und ein Diskontsatz, der durch marktmassige oder politische Wahl abgeleitet wird, tendiert dazu, konsistent und irrational den Zukunftskonsum unterzubewerten. Ein Diskontsatz sollte dem durchschnittlichen vorhergesagten Wert eines Zukunftsproduktes in Verbindung setzen zu dem Gegenwartswert des gleichen Produktes. Durch die Vorhersage von Preistrends und dem Grenznutzen des Geldes und durch die Unterscheidung verschiedener Unsicherheitseffekte konnen unterschiedliche Satze fur verschiedene Produkte berechnet werden. Die Satze fur landbezogene Produkte sind wahrscheinlich niedrig, und solche Satze verandern die gegenwartig festgelegten absoluten und relativen Werte fur verschiedene Landnutzungen.

The various levels of organisation which may be distinguished in non-crystalline block copolymers are considered. An account is given of the application of low-angle X-ray diffraction and electron microscopy to the characterisation of the two-phase morphology and grain texture of some styrene/isoprene copolymers. The first group of copolymers to be considered contains two series of samples of the type S–I, (S–I–)2X, (S–I–)3Y, and (S–I–)4Z where I is polyisoprene, S polystyrene and X, Y and Z are di-, tri- and tetra-functional coupling groups. The second group of copolymers which was subjected to a less detailed study than the first consists of just two polystyrene-g-polyisoprene samples.

The dilute solution properties of several fractions of poly(propylene oxide) have been determined in two solvent systems; hexane at 46°C and iso-octane in the temperature range 46° to 89°C. In general these properties show no dependence on the degree of tacticity of the fractions. An exception is the second virial coefficient measured by light scattering in hexane at 46°C, which varies considerably from fraction to fraction. A tentative explanation, in terms of the incipient crystallization of the polymer, is advanced to account for this anomaly.

Samples of natural rubber were vulcanized in the presence of n-decane, decalin and o-chlorobenzene. The diluents were then removed, and the force-extension characteristics of the samples studied over the range 1·1

The physical properties of the poly(epoxides) are summarized, and compared with each other and also with the properties of the corresponding poly(olefins). The nature of the side group has little effect upon the dynamic and equilibrium flexibilities of the poly(epoxides) unless the side group is bulky, e.g. t -butyl and phenyl.

A graft copolymer was prepared by adding poly(isoprenyl lithium) to chloromethylated polystyrene. Four samples, isolated from the product by a liquid-liquid separation scheme, were characterized with respect to molecular weight and chemical composition. The intrinsic viscosities of the samples in methyl cyclohexane and n-decane were studied over a range of temperatures. On cooling in both solvents the results suggested that before the temperatures of liquid-liquid separation were reached segregation and partial collapse of the polystyrene main chains occurred.

Poly(ethylene oxide) has been fractionated by crystallization from dilute solution in several solvents. Fractionation with respect to molecular weight is slight: there is a tendency for lower molecular weight polymer to crystallize first. The mechanism of crystallization of poly(ethylene oxide) from dilute solution is discussed briefly, and the application of fractional crystallization to both nominally crystalline and partially crystalline polymers is considered.

Block copolymers having structures of the type A-B, (A-B-) 2 X, (A-B-) 3 Y and (A-B-) 4 Z, where A is polystyrene, B is polyisoprene, and X, Y and Z are linking agents, have been synthesized by anionic polymerization. Electron microscopy of thin films cast from benzene solutions showed that all the polymers formed ordered arrays of regular domains. The inter-domain distances and domain radii of the two phase structures were not influenced by changes in chain geometry, provided the overall composition and the length of the A blocks remained constant. Some results are reported concerning the compatibility of polystyrene/polyisoprene and polystyrene/polybutadiene block copolymers.

Intrinsic viscosity and light scattering data are reported for fractions of poly(propylene oxide) in a theta solvent, isooctane at 50°C. These results are used to obtain a value for the unperturbed dimensions of poly(propylene oxide), i.e. ( r 2 M ) 1 2 =0·80 A .

Thermoelastic measurements have been made at constant volume on lightly crosslinked poly(dimethyl siloxane). The results show that 25 per cent of the retractive force is energetic in origin.

A study has been made of the domain morphologies of two block copolymers of the type, (styrene) x (butadiene) y (styrene) x ; for the first sample the weight-average molecular weights of the styrene and butadiene blocks were 13 300 and 75 000 respectively, whilst for the second sample they were 10 300 and 71 000 respectively. The morphologies of films cast at different rates of evaporation from benzene solution were investigated by electron microscopy. With the exception of those prepared at very high rates of evaporation, the films formed highly regular domain structures, which were subdivided into grains. Low-angle x-ray studies were made on both solvent cast and compression moulded test pieces. It was found that at the tertiary level the latter consisted of an hexagonal lattice of glassy cylinders embedded in a rubbery matrix. The solvent cast test pieces also formed a regular domain structure, but for these it was not possible to make a definite structural assignment. Finally an attempt was made to trace the interrelationship between the force-extension behaviour of the samples and the morphology.

The coefficients of isothermal compressibility, cubical expansion and thermal pressure, have been measured for lightly crosslinked butyl rubber over a range of temperatures and at several elongations. The “network contribution” to these coefficients is found to be negligibly small as predicted by analyses based on either the Mooney-Rivlin or Gaussian equations of state.

A method has been developed for studying the presence of micellar aggregates in block and graft copolymers. Specimens for examination in the electron microscope were prepared using a freeze-etching/replication technique. Four well-characterized copolymers were studied: a polystyrene-polyisoprene two-block copolymer, a (polystyrene-polyisoprene-) 4 Si star-block copolymer, and two polystyrene-g-polyisoprene graft copolymers. Technical white oil, which is a very poor solvent for polystyrene, was taken as the solvent for the copolymers. For the purpose of comparison, a study was also made of specimens prepared from polystyrene homopolymer dissolved in a 1:1 mixture by vol of technical white oil and toluene.

Binary ABA block copolymers where the central block is elastomeric possess a range of characteristic textures when observed as osmium tetroxide stained thin films (40 nm) in the electron microscope. A study of low styrene content samples (∼25%) prepared from dilute solution indicated three basic morphologies: an irregular phase structure, arrays of linear and hexagonally-packed circular styrene domains. The observed texture was a function of rate of preparation, decreasing rates resulting in greater domain ordering. Domains varied in size from 10 to 24 nm with corresponding spacings in the range 10–45 nm. Grain structure was only clearly observed in arrays of circular domains but quasi-spherulitic patterns occurred in linear morphologies. Coherent and random multilayers were also observed, in some cases giving rise to Moire fringes. Comparison of observed and calculated area fractions from dilute solution characterization implied a rod-like domain structure, although significant errors were introduced by strains in the thin films.

Global warming is becoming a reality, with growing evidence that anthropogenic activity on our planet is starting to influence our climate (IPCC, 2001). Due to the increase in significant weather-related disasters in recent years, it is important to investigate the role of global warming on such changes. In this paper we attempt to estimate the long term trends in lightning activity over tropical Africa during the past 50 years, using upper tropospheric water vapor as a proxy for regional lightning activity. We use the NCAR/NCEP reanalysis product available for the period 1948 to the present to estimate the long term trends in lightning activity. Similarity between the long term African lightning variability and observed rainfall and river discharge variability are demonstrated. Since 1950 the inferred lightning activity over Africa shows significant variability, reaching a maximum during the 1960s, followed by a decrease in activity during the following 30 years.

The dependence of the critical micelle temperature, c.m.t., on concentration was determined for four polystyrene-block-polyisoprene copolymers in n-hexadecane. The results were used to estimate the standard free energies of micellization, ΔGθ, and the standard enthalpy, ΔHθ, and entropy contributions, −TΔSθ. The values of ΔGθ and ΔHθ were found to be strongly dependent on the molecular weight of the polystyrene block, both becoming more negative as the molecular weight increased. Increasing the molecular weight of the polyisoprene block was also found to make ΔHθ more negative but it had a negligible effect on ΔGθ.

The thermodynamics of micelle formation by a polystyrene-b-polyisoprene block copolymer in N,N′-dimethylacetamide, which is a selectively bad solvent for polyisoprene, has been investigated. The micelles have a very narrow size distribution enabling the association process to be treated as a single-stage equilibrium. The temperature dependence of the critical micelle concentration was determined from measurements of scattering intensity against temperature carried out at six concentrations within the range 2.3 × 10−7 to 1.2 × 10−4 mol dm−3. A plot of 1n (c.m.c.) against T−1 gave a value for the standard enthalpy of micellisation (per mole of copolymer chains in the micelle) of − 153 ± 6 kJ mol−1. The standard entropy contribution (-TΔSΘ) to the standard free energy of micellisation was found to be positive. These results are in strong contrast to those reported for synthetic surfactants in aqueous media for which a favourable standard entropy change is the factor mainly responsible for micelle formation.

Coefficients of expansion and internal pressures (Pi) have been measured for samples of poly(ethylene oxide) of molecular weight (Mn) 2000, 6000 and 20000. The values of Pi found for the solids (Pi < 108 Pa, 10°) are low compared to those found for the liquids (Pi ⋍ 5 × 108Pa, 70°).

A study was made of the solubilisation of some polystyrene homopolymers in a paraffinic base oil containing polystyrene-b-poly(ethylene/propylene) copolymer micelles. The solubility was found to be dependent on the molecular weight of the polystyrene homopolymer and on the amount of the copolymer in solution. There was no significant solubilisation of a polystyrene homopolymer (Mn = 63,000 g mol−1) having a molecular weight greater than that of the polystyrene blocks (Mn = 35,000 g mol−1).

Samples of fluid polystyrene are converted into the glassy state at 20°C. and 1 atm. pressure by two different routes: (a) by cooling at 1 atm. pressure and (b) by cooling at 1250 atm. and then decompressing. The heats of solution of the samples are determined in toluene at 30°C. The samples are found to have similar enthalpies, although their densities are different. An attempt is made to explain the results in terms of freezing of rotational isomerism at the glass transition temperature.

Force-pressure measurements at constant length and temperature have been made on a sample of crosslinked cis-polybutadiene in the range1·11

Landscape values tend particularly to be under discussion at times of change. Change focuses attention and galvanises groups into action. Proposed changes of land use are the basic material of statutory planning control. Unless change is contemplated, the values of alternative forms of landscape are only of academic interest.

Events overtake the condition of the landscape, and change the reactions of consumers to that landscape. Values calculated by the expert as valid for today will not always be a correct assessment.

The ‘expert ’ is a quintessential character of modern life. Such are the complexities of every narrow sphere of human activity that it is beyond the means of any one person to be familiar with more than a small fraction of available knowledge and experience. So it is in technical matters, and so it is in matters of judgement. When a piece of landscape has to be evaluated, it is far easier, cheaper, and quicker for society to employ an expert in aesthetics than to assemble and analyse the opinions of all concerned. Especially when there are qualitative divergences of opinion between landscapes ’ consumers, convenient resolution lies in ex cathedra judgements, delivered by one whose aptitude for and training in a subject make his opinions authoritative.