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At the present two Swedish group solar heating plants with seasonal storage, connected to residential areas with about 50 single-family houses, have been in operation for four years. The Lambohov Plant has a total of 2700 m2 of flat plate collectors and a 10000 m3 rock pit store. The Ingelstad plant has a total of 1300 m2 of concentrating collectors and a 5000 m3 free-standing tank. The emphasis of the assessment has been on system performance as a whole. Most of the emphasis has been placed on general conclusions concerning technology and economy for seasonal storage plants.

Effective solar U-values are introduced, permitting a simple calculation of building heat loads and accounting for solar heat gains as well. This can be done by multiplying the normal U-values of walls and windows with special reduction factors. They are determined by a rational procedure and depend on climatic and building-related parameters. An application of the solar U-value concept to the case of a facade shows how heat loads, various influences and optimum fenestration percentages can be predicted.

The objectives of using chemical processes in solar-thermal facilities are derived. The possible applications of these chemical processes are given under the boundary aspects of meteorology and operating conditions. Radiative and thermal energy transfer procedures are considered.

Dehydration of vegetation varies in degree according to its intended function and the money available in production. Many countries have part of the year in which there is sufficient solar heat and dry air for drying by exposure. If vegetable tissue can be dried down to an equivalent of 70% relative humidity, micro-organisms cannot find sufficient moisture to be active and some insects are less effective as destructive consumers. The equivalent moisture content varies with the tissue but is mainly of the order of 10–12%. Where climates are unkind and do not offer dry heat it is necessary to use forced drying, but this is made difficult by the relatively low world prices for bulk commodities sold into a competitive market.

A wide range of solar technologies capable of delivering thermal energy at temperatures from 30°C to 600°C and above have been developed. Active solar technologies, which encompass the low end of this temperature range (30°C–120°C), have been technically proven for water and space heating applications, and, where economical, have gained a measure of commercial success. Promising active solar cooling technologies have also been introduced, but remain largely developmental. Solar thermal technologies, which encompass the temperature range from 100°C and above, have been demonstrated in applications ranging from industrial process heating to utility electricity generation. Distributed and central receiver solar thermal systems have been constructed capable of generating electricity in the multimegawatt range. This paper reviews the recent advances and future prospects for both active solar and solar thermal technologies. Although based largely on the United States experience, solar technology developments from other nations are also included.

In the Netherlands a study has been carried out on the feasibility of seasonal storage of solar heat using the soil as storage medium. This study was carried out in the period January 1978 to July 1980 by the Delft Soil Mechanics Laboratory in cooperation with Philips Eindhoven and the Institute of Apllied Physics (TPD-TNO-TH) in Delft.

The objective to decrease the cost of distillation by the use of solar heat and a vacuum system combined was achieved. My original design of a single pot type still was altered during construction by dividing the distillation tank into three sections with a condenser coil after each section so that 160+ proof alcohol can be acquired without extensive reflux. However, some reflux will still be necessary to extract the most alcohol possible from the mash. This proto-type still could be reproduced for use as an On the Farm Plant if the components are size matched and the modifications are incorporated as I have outlined in Conclusions and Recommendations on page No. 4 of this report.

This project consists in the development of design methods of solar plants for heating of housing by means of the interseasonal storage of solar energy through water tanks located under or above ground. In this report the two-dimensional transient conduction PACI computer code for cylindrical tanks is described and some results are commented on.

The thermal behaviour of common building forms is well known but this behaviour is altered when buildings are laid out in clusters. The overall building form, the extent of glazed and unglazed surface area, the building orientation and the proximity of other buildings determine solar heat gains to the building. A geometrical property of the building called solar exposure can be used to determine relative effi ciency of different types of building clusters in both warm and cold climates. For air-conditioned and/or heated buildings the solar exposure bears a direct relationship to the energy used for heating and air-conditioning, but no such relationship exists between discomfort (or comfort) obtained in non air-conditioned buildings in warm climates and the building solar exposure. However, it is found that solar exposure per unit surface area of building is related to the discomfort index and the former is therefore a good indicator of the relative thermal performance of buildings in different urban layouts. Extended building forms with large external surface areas are useful in hot climates, but even better results can be obtained when compact forms are used with highly articulated surfaces.

The accomplishments of a program of continued development of a solar heat supply system employing a faceted fixed mirror concentrator (FFMC) are summarized. This concentrator has provided heated air at several hundred degrees Celcius with efficiency exceeding conventional collectors. Under this contract the prototype FFMC was fitted with a liquid-heating receiver which employs evacuated tubular collectors of high efficiency. The new contract was initiated in March 1976 with a subcontract to Scientific-Atlanta to: (1) fit the concentrator with a receiver using a selective absorbing surface and a liquid collecting medium, (2) develop a mechanical design based on mass production manufacturing techniques, (3) develop cost estimates to produce this design, and (4) predict annual performance of the resulting collector. Progress is reported.

In Groninqen, the Netherlands, a project with seasonal heat storaqe of solar heat in the upper layer of the soil has been realized [1]. The project involves 96 solar houses, each with 25 m 2 of high performance solar collectors mounted on the south facing roofs, and a seasonal heat store of about 23,000 m 3 (depth 20 m) of water saturated sandy soil. The seasonal heat store in the soil consists of a layer of soil in which a vertical tube heat exchanger is inserted. The Groningen project has been realized in two phases: - The construction and testing of the seasonal heat store. In 1983, when the seasonal store was ready, the experimental phase started. Heat input and heat output of the store were simulated with a boiler and a cooler. - The construction of the solar houses and the coupling to the seasonal heat store. By the end of 1984 the system as a whole was in full operation. This paper describes the solar heating plant as a whole. Design backgrounds are given in brief. The practical experience with the operation of the seasonal heat store is discussed. Finally, the first results of the monitoring phase are given.

An improved technical assessment of active solar heating — space heating and domestic hot water (DHW) with hydronic systems — in the various climatic zones of Switzerland and, hence, of Central Europe is presented and the identified important technical factors determining the amount of solar heat which can be effectively used in a system are described. We used a combined experimental and theoretical approach: (i) We measured the thermal performance of nearly 100 different collectors on our test facility and we monitored the thermal performance of approximately 20 commercial solar energy systems located at various places in Switzerland; (ii) We developed and validated a simplified model to predict the all-day performance of a collector in a given climate under known operating conditions. The resulting upper limits for the useful solar heat have been found to vary by a factor of 4. This points out the essential role of system optimization in order to achieve the breakthrough of active use of solar energy. We further conclude that no global assessment of the potential of this technology is possible in Central Europe; a detailed analysis is required.

The automated Venetian blind window system consists of a double glazed unit incorporating louvers hermetically sealed between two glass panes. In this paper, a simplified design method for sunspaces is carried out, based on the results obtained with the thermal model developed earlier by Rheault and Bilgen (1987). The simplified method is based on the calculation of the solar heat gains through a window system by the ASHRAE method (1981). The hourly optimum louver angles for minimum auxiliary energy requirements are determined with the thermal model; then the associated shading coefficients (SC) and thermal resistance (Rtop) are computed and used to evaluate the solar heat gains through the louvered system. The application of the simplified method is illustrated using a sunspace in the Montreal region and the results are compared to a reference system without automated Venetian blind. The results indicate a considerable system thermal improvement.

The initial project phase, a pre-study, has recently been carried out concerning technology and economics for a very big solar heating plant planned to be in operation around 1990 in the town of Kungalv in the west of Sweden. The essential aim of the project is to present a feasible system concept featuring substantial solar heat coverage for the entire building stock of the town. About 50 % of the total building space is planned to be heated by the central solar heting plant. The annual energy requirement is 52 GWh including residential houses for 6000 inhabitants and 115 000 m 2 of buildings for commerce, municipial service and industry. The preliminary outlined plant design employs 116 000 m 2 of high-temperature flat plate solar collectors and 380 000 m 3 of waterfilled rock caverns for seasonal heat storage. The plant is connected to an extensive district heating network. The design objective is to meet 75 % of the annual heating requirement by solar energy and the rest by fossil fuelling. The calculated cost of the heat produced by the plant is SEK 0,42/kWh (1 SEK ≈ 0,16 US$).

Transparently insulated massive walls reduce heating loads to an impressive degree. The heating season of a building can be shortened by several months. Good transparent insulation materials (TIM's) have transmittances of up to 70 percent for diffuse irradiation and U-values in the range from 0.5 to 1.5 Wm−2K−1.The combined effect of thermal insulation and collecting solar radiation allows the use of these materials not only for southern, but also for other orientations. Steady-state theory gives upper limits for the potential of this passive component to reverse the heat flow towards the interior. Experimental data indicate that it may be applied for periods greater than the time constant of the wall. Apart from overheating in summer, which makes some shading device necessary in most cases, there is always some mismatch between solar heat gains and heating demand. This leads to a non-utilizable fraction of the solar gains. Simulations allow the inclusion of dynamical, non-linear effects and non-utilizability depending on the storage capacity of the system, but easy and rapid design methods are desirable. The Solar-Savings-Fraction method of Heidt (1985) and the method of Monsen (1982) shall be compared with simulation results. Results show that the most relevant parameters can be incorporated in the steady-state theory. Corrections are due to the storage capacity of the house, which influences utilizability especially in spring and autumn. The wall heat capacity has little influence on heat gains, but determines the maximum absorber temperatures.

A small solar heat engine designed by the authors consisted of a small solar furnace and a Stirling engine; the fabricating apparatus for the parabolic mirror was reported in the last conference of 13th 'Ea") In this paper, the construction for this solar furnace and the efficiency of the Stirling engine are reported.

Black selective solar energy absorbers are usually metallic mouldings carrying one or more special coatings. The nature of the composite leads to problems of high IR emissivity, low stability and high cost. The purpose of this project is to solve these problems by showing that a selective surface may be produced simply by controlling the topography of a metallic absorber.

Selected results of a multi-year, multi-organization program of solar heating system development based mainly on experimental and demonstration projects supported by the Office of Solar Heat Technologies of the U.S. Department of Energy are presented. The capabilities of various types of solar water heating and space heating systems are compared, the low performance of most systems in practical use is contrasted with that of well designed experimental systems, and opportunities for improving the average efficiency of solar heating are shown There is a trend toward considerably better average performance and toward higher efficiencies of the best systems in practical use. It is concluded that even without major design changes or system cost increases, there are excellent prospects for significant increases in average performance of solar heating systems.

Although some thought has been given to clothing hygiene over the last two centuries, specific garments for the tropics are a matter of the last fifty years. “Flannel next the skin” was worn until almost recent times because it was believed that wool, by combating the “cold dews of the dawn” and the chills arising from sweating, prevented diarrhoea and dysentry. Hence the origin of the flannel or “cholera” belt. Fear of the sun's rays penetrating bone and entering the central nervous system led to the use of the sun helmet and the now forgotten spine pad. Sun glasses have been used on and off for a century to prevent ophthalmia and even sunstroke. The warmth of a textile material is independent of its chemical nature and due mainly to the air clinging to the surface of the fibres and yarns and to that in the interstices. In the case of natural fibres (wool, cotton, linen and silk), vapour and liquid water pass not only through the air interstices but will be rapidly absorbed into the fibre substance. Hence these materials, even in tight weaves, do not feel particularly damp to the skin in the presence of sweating. On the other hand, continuous-filament synthetic materials (nylon, Terylene, etc.) take up very little water into the fibre substance, and in tight weaves do not absorb moisture easily. Thus, in the presence of continuous sweating, prickly heat and fungus skin infection may be aggravated. Special manufacturing techniques allow synthetic fibres to be woven into porous materials which transmit sweat efficiently by a wicking process. The good properties of synthetic fibres (hard wear, non-shrink, drip-dry), however, show themselves best in blends with wool, cotton or linen which make suitable light weight materials for socks, underwear and outer garments for the tropics. In a hot climatic chamber, nudity is associated with less sweat production than when wearing clothing. However, in the damp tropics, clothing increases the efficiency of evaporation, and loose garments aid convection and ventilative cooling. When in the jungle, protection may be required from flora and fauna. For this, thin tight weaves (of natural fibres) are suitable and are as cool as are thicker but open materials. Under desert conditions clothing acts as a tent, and keeps hot air, sand and flies, solar heat and ultra-violet radiation away from the skin. Light-coloured clothing reflects solar heat better than dark clothing but the effect may be less than generally believed. Good protective footwear is required for the hot sand of the desert. Any light-weight hat is suitable for the tropics, and sunglasses are of value in the presence of glare and blown sand.

Solar heat loads on seated subjects, wearing hot-weather uniforms in various colors, were determined during a series of 30 three-hour experiments in the desert near Yuma, Arizona. Black and white uniforms were compared during one summer, green and khaki during the next. The conclusions were derived from sweat evaporation data in sun and shade, assuming that evaporative heat loss e aled the total heat load. The calculated solar heat loads were 145-kg-cal/hr and 92 kgcal/hr for black and white uniforms, and 113 kgcal/hr an 92 kg-cal/hr for green and khaki. In terms of the total heat load on the man, the differences with color represented increases of only 17% for black over white, and 7% for green over khaki. The white uniform had much less advantage than fabric reflectance measurements would indicate, possibly because multiple reflections in the vicinity of folds and creases increased the amount of radiation absorbed.

MR. H. A. PHILLIPS, in NATURE, vol. xxvii. p. 127, thinks that the effect of the increasing quantity of hydrocarbons in the air from the combustion of coal will be to make climates more extreme. It seems to me the effect will be the direct contrary. Gaseous and vaporous hydrocarbons absorb heat much more powerfully than air, and whatever makes the atmosphere absorb and retain more solar heat than at present will tend to equalise temperatures between day and night, and also between different latitudes. I think, however, that any possible effect of hydrocarbons will be quite insignificant in comparison with the effect of the watery vapour of the atmosphere, which, as Tyndall has shown, moderates climates by its power of absorbing solar heat.

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SIR ERNEST RUTHERFORD in his book “Radioactive Substances and their Radiations” has suggested the possibility that solar heat may be supplied from radioactive energy derived from elements which had become radioactive under the extreme thermal conditions prevailing.

IN your last week's issue Mr. Hardy directs attention to the fact that no Becquerel rays can be detected from the sun, and regards this as an objection to the view that the solar heat may be accounted, for by the presence of radium.

To utilize solar energy advantageously for the lighting and heating of buildings, additional data are required on the availability of daylight and solar heat for variously oriented surfaces and for numerous geographical locations. This study presents data on daylight availability at Ann Arbor, Michigan for the period March 1953 to March 1954 and correlates these data with theoretical considerations and climatological data as recorded by the U. S. Weather Bureau.

Having considered the bearing of the theory of hydrostatic equilibrium on internal structure of the Moon, and compared its consequences with available observations, let us turn now to investigate the conclusions which can be drawn from an application, to the Moon’s interior, of the principle of the conservation of energy in so far as the internal temperature in lunar interior is concerned.

EIGHT BITUMINOUS MATERIALS, CONSISTING OF ASPHALT CEMENTS, LIQUID ASPHALTS AND TARS WERE EXPOSED IN LAYERS APPROXIMATELY ONE EIGHTH INCH IN THICKNESS IN SHALLOW CONTAINERS PLACED IN GLASS-COVERED BOXES TO THE ACTION OF LIGHT, AIR AND SOLAR HEAT. THE EXPOSURES BEGAN IN DECEMBER AND CONTINUED FOR ONE YEAR. THE EXPOSED SAMPLES WERE REMOVED AT VARIOUS INTERVALS AND THE CHANGES IN WEIGHT AND CONSISTENCY DETERMINED. THE PERCENTAGE GAIN IN INSOLUBLE ORGANIC MATTER WAS ALSO DETERMINED. THE SOLUBILITY OF THE ASPHALTIC MATERIALS WAS DETERMINED BY 86 DEGREE B-NAPHTHA AND THE TAR PRODUCTS BY CARBON DISULFIDE. TEST DATA SHOWED THAT THE HARDENING OF ALL BITUMENS UPON EXPOSURE IS NOT DUE TO LOSS BY VOLATILIZATION OF THE LIGHT CONSTITUENTS ALONE, AND THE INCREASE OF INSOLUBLE MATTER IN THE TWO SOLVENTS INDICATE THAT OXIDATION CONTRIBUTES TO THE DEVELOPMENT OF INSOLUBLE MATTER IN THE ASPHALTIC AND TAR PRODUCTS.

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According to modern data water ice is the main constituent of cometary nuclei. The rate of its evaporation determines the rate of liberation of other constituents, including those that determine the photometric properties of comets. The estimates of the total mass loss per perihelion passage seem to give values about one order of magnitude smaller than those necessary to explain the nongravitational forces as due to the reactive force of material leaving the nuclei. Thus the conventional explanation of the nongravitational forces deserves further study from the point of view of the physical theory of comets.

This report covers the development of an experimental low cost green solar reflectant and low visibility coating for use on missile systems. The currently specified enamel based on a special and single source pigment, cobalt titanate, has a raw material cost of approximately $9 per gallon compared to $1. 50 per gallon for the experimental material. In addition the test data indicated the experimental material to have a 2 - 3F. advantage over the currently specified material. Exterior exposure and field tests are in progress.

Decentralized surplus feed-in of solar heat into a District Heating Network (DHN) is here addressed. The heat collected from solar panels located on rooftops of DHN connected buildings may either be used locally for domestic hot water and space heating or fed into the DHN. Two-way substations able to transfer heat from and into the network seem then to be required utilities. The present paper presents the specifications (60kW capacity, return-to-supply connection) and promising architectures of such two-way substation based on a previous analysis. A first-of-a-kind Modelica-based dynamic model of the substation together with the consumer and the solar field connected to it is then detailed. Two-day simulations considering real operating conditions of DHN were then performed. The results highlighted i) the good match between the periods of solar heat reinjection with the periods of low supply temperature and differential pressure and ii) the decisive benefit of the reinjection to increase the part of useful solar energy.

Orientation with respect to the sun has been observed in a wide range of species and has generally been interpreted in terms of thermoregulation and/or ultraviolet (UV) protection. For countershaded animals, orientation with respect to the sun may also result from the pressure to exploit the gradient of coloration optimally to enhance crypsis.Here, we use computational modelling to predict the optimal countershading pattern for an oriented body. We assess how camouflage performance declines as orientation varies using a computational model that incorporates realistic lighting environments.Once an optimal countershading pattern for crypsis has been chosen, we determine separately how UV protection/irradiation and solar thermal inflow fluctuate with orientation.We show that body orientations that could optimally use countershading to enhance crypsis are very similar to those that allow optimal solar heat inflow and UV protection.Our findings suggest that crypsis has been overlooked as a selective pressure on orientation and that new experiments should be designed to tease apart the respective roles of these different selective pressures. We propose potential experiments that could achieve this.

Decentralized surplus feed-in of solar heat into a District Heating Network (DHN) is here addressed. The heat collected from solar panels located on rooftops of DHN connected buildings may either be used locally for domestic hot water and space heating or fed into the DHN. Two-way substations able to transfer heat from and into the network seem then to be required utilities. The present paper presents the specifications (60kW capacity, return-to-supply connection) and promising architectures of such two-way substation based on a previous analysis. A first-of-a-kind Modelica-based dynamic model of the substation together with the consumer and the solar field connected to it is then detailed. Two-day simulations considering real operating conditions of DHN were then performed. The results highlighted i) the good match between the periods of solar heat reinjection with the periods of low supply temperature and differential pressure and ii) the decisive benefit of the reinjection to increase the part of useful solar energy.

The statistical distributions of solar irradiation accumulated over periods of consecutive days were determined for Lisbon according to the number of days and the long-term clearness index. These distributions were found of interest in connection with the design of storage capacity associated with solar heat collecting systems to guarantee desired heat output rates. A statistical analysis of time series of daily solar irradiation sums observed in Lisbon was carried out. Evidence is obtained for a medium-term correlation (for at least 10–15 days long) and for short- and medium-term periodicities (of about 3 and 10–15 days). A zeroeth order Markov chain does not account for the observed behaviour and a first order Markov chain neither, except perhaps in the short term in July.

Heterothermic insects like honeybees, foraging in a variable environment, face the challenge of keeping their body temperature high to enable immediate flight and to promote fast exploitation of resources. Because of their small size they have to cope with an enormous heat loss and, therefore, high costs of thermoregulation. This calls for energetic optimisation which may be achieved by different strategies. An ‘economizing’ strategy would be to reduce energetic investment whenever possible, for example by using external heat from the sun for thermoregulation. An ‘investment-guided’ strategy, by contrast, would be to invest additional heat production or external heat gain to optimize physiological parameters like body temperature which promise increased energetic returns. Here we show how honeybees balance these strategies in response to changes of their local microclimate. In a novel approach of simultaneous measurement of respiration and body temperature foragers displayed a flexible strategy of thermoregulatory and energetic management. While foraging in shade on an artificial flower they did not save energy with increasing ambient temperature as expected but acted according to an ‘investment-guided’ strategy, keeping the energy turnover at a high level (∼56–69 mW). This increased thorax temperature and speeded up foraging as ambient temperature increased. Solar heat was invested to increase thorax temperature at low ambient temperature (‘investment-guided’ strategy) but to save energy at high temperature (‘economizing’ strategy), leading to energy savings per stay of ∼18–76% in sunshine. This flexible economic strategy minimized costs of foraging, and optimized energetic efficiency in response to broad variation of environmental conditions.

Seasonal solar thermal energy storage (SSTES) has been investigated widely to solve the mismatch between majority solar thermal energy in summer and majority heating demand in winter. To study the feasibility of SSTES in domestic dwellings in the UK, eight representative cities including Edinburgh, Newcastle, Belfast, Manchester, Birmingham, Cardiff, London and Plymouth have been selected in the present paper to study and compare the useful solar heat available on dwelling roofs and the heating demand of the dwellings. The heating demands of space and hot water in domestic dwellings with a range of overall heat loss coefficients (50 W/K, 150 W/K and 250 W/K) in different cities were calculated; then the useful heat obtained by the heat transfer fluid (HTF) flowing through tilted flat-plate solar collectors installed on the dwelling roof was calculated with varied HTF inlet temperature (30 °C, 40 °C and 50 °C). By comparing the available useful heat and heating demands, the critical solar collector area and storage capacity to meet 100% solar fraction have been obtained and discussed; the corresponding critical storage volume sizes using different storage technologies, including sensible heat water storage, latent heat storage and various thermochemical sorption cycles using different storage materials were estimated.

Ethanol production sites utilizing sugarcane as feedstock are usually located in regions with high land availability and decent solar radiation. This offers the opportunity to cover parts of the process energy demand with concentrated solar power (CSP) and thereby increase the fuel production and carbon conversion efficiency. A plant is examined that produces 1st and 2nd generation ethanol by fermentation of sugars (from sugarcane) and enzymatic hydrolysis of the lignocellulosic residues (bagasse), respectively. Enzymatic hydrolysis is a promising alternative for 2nd generation biofuels due to its high conversion efficiency and low environmental impact. In conventional ethanol production processes, electrical and thermal power is delivered to the system by burning parts of the feedstock to drive a steam based cogeneration cycle (between 400 and 800K). Introducing high temperature thermal power (at 800K) from a solar trough field coupled with sensible heat storage, for continuous operation, offers the opportunity to replace the heat generated from biomass burning, and thus increase the product yield. In this work, the potential for process integration of a solar trough field coupled with packed bed thermal storage to a 1st and 2nd generation ethanol production site is evaluated by means of pinch analysis. Decision parameters such as the solar fraction, the percentage of bagasse to 2nd generation, and the solar field size are optimized via multi- objective optimization based on evolutionary algorithms to maximize the carbon conversion efficiency and minimize the total annual cost for a plant located in Ribeirao Preto, Brazil.

The method of treating trachoma by exposure to the concentrated rays of the sun, is here recommended and described. Such rays are more potent than those of the electric light, which may, however, be substituted when solar rays are not obtainable. The applications include solar heat, which must not be applied in excess. They are especially valuable in the treatment of corneal ulcers that appear in this disease.

A study has been made of optical aspects of airport control towers as part of a planned general optimization of control towers by Transport Canada. Problems found were reflections, glare, visual obstructions, identification of distant objects, and excessive solar heat. The study makes recommendations on cab shape, tower height, glazing, shades, sunglasses, binoculars, and internal lighting. Proper choice of cab shape (e.g., 30 degrees window inclination and 12-28 sides) provided effective control of reflections. Some plastic shades werefound to increase the risk of eye damage. Two tower cabs incorporating the recommendations have been built and were found to be satisfactory.

Through the kind generosity of Harry O. Wood and the manufacturers of the Wood-Anderson seismometer, Fred C. Henson Company, a long-period instrument was loaned to Canisius College for a study of building-tilt under the influence of solar radiation. These tests were continued through the summer of 1932, but definite measurements of tilt due to solar heat revealed complications not attributable to this cause directly. The study was continued during winter months under conditions of artificial heating in the building, and it was found that even slight temperature-changes caused appreciable shifting of the zero. Whether this shift is due to building-tilt, or solely to a temperature-effect in the instrument, has not been determined.