CLIMATE, ARTIFICIAL. The usual significance of the word climate is to indicate the result of all the solar and terrestrial influences or factors which affect animal or vegetable life. These factors include temperature and humidity; gaseous composition; pressure and movement of air; light intensity and quality. An arti ficial climate may be similarly defined as a more or less mechani cal control of one or more of these factors in a comparatively restricted space independent of and in contrast to the natural climate at that particular location. In a broader sense the appli cation of air conditioning to industrial processes might be included under the term artificial climate. In some processes such as the textile industries large quantities of energy, used in driving, spin ning and weaving machinery, are liberated as heat in a relatively small space. Air conditioning is important in this case both to provide a liveable humidity and temperature for the employee, and a suitable temperature and humidity for working the fibre. (See AIR CONDITIONING.) In a more restricted sense artificial climate, as it affects animal or vegetable life, has a more limited application. The mechanical control of temperature and humidity has been used in theatres, schools, churches and other similar public meeting places to insure the comfort and well-being of the audience at all seasons of the year. For this work it has been found that a temperature of about F and a relative humidity of 55% is most comfortable for the average person in summer, while 7o° F and 35 to 4o% relative humidity are the most satisfactory in winter. In the crowded theatre the problem both summer and winter is to get rid of the heat generated. The average individual radiates sufficient energy as heat to raise the temperature of 3o cu.ft. of air approximately 9° F per minute. From this it is calculated that about 3o cu.ft. of air per person per minute is necessary. The incoming air is nor mally supplied at a temperature a few degrees lower than the opti mum for comfort so that it can function in removing heat from the audience. The air intakes or positive pressure supply openings are usually placed in the ceiling of the room, while the exhaust duct or negative pressure openings are distributed more or less uni formly along the floor, beneath the seats. There is also need for humidification of air in dwelling houses in winter, as it has been shown that air taken from the outside at a temperature of 3 2 ° F or less and heated to 7o° is, in general, much too low in humidity for human comfort. Mechanical devices for spraying or other wise introducing additional water vapor in appreciable amounts are now used for this purpose.
Light has been used in the treatment of human diseases, since Finsen studied the effects of various regions of sunlight and arti ficial light sources during the years 1893 to 1904. More recently (1918-22) Huldschinsky, Hess and others have shown that the extreme ultra-violet region of sunlight (wave-length 312 to 290 millimicrons) is effective in the cure of the disease rickets, quite generally in animals, and particularly in human beings. Since this time the control of light intensity and quality along with air conditioning has been used in sanitaria and solaria for the treat ment of specific diseases and as a general tonic, both physical and mental in its effects on the individual. Human patients have been treated at the Battle Creek sanitarium, Battle Creek, Mich., for several years with a typical installation of this sort. Four carbon arc lamps of about 22 amperes current consumption placed at a distance of 3oin. from each patient are used in general irradiations at this institution. The air temperature is regulated to about 78° F and relative humidity is maintained at about 7o%. The quality of light output of the carbon arc lamps can be altered within limits by using carbons impregnated or cored with different metallic salts. Carbons cored with cerium fluoride are commonly used in the production of a light source which approximates sunlight very closely, both in the visible and ultra-violet regions. More of the extreme ultra-violet beyond wave-length 290 millimicrons can be added by the addition of iron to the core material. Mercury vapour arcs in quartz tubes have also been generally used for irradiating human patients. This light source includes the extreme ultra violet region which is not found in sunlight and has in addition several bright lines in the visible region and the near ultra-violet. It does not, however, approach sunlight in colour distribution.
The volume concentration of oxygen gas in air has been accu rately regulated in hospital rooms designed for the treatment of pneumonia patients at the Rockefeller Institute for medical re search, New York city. Oxygen is maintained at about 4o% or about twice the normal concentration of the atmosphere in these rooms. The use of such an atmosphere is often successful in sup plying sufficient oxygen to the lungs of a patient whose effective lung capacity has been greatly diminished by the disease. Arti ficial climate has been used at the Boyce Thompson institute for plant research, Yonkers, N.Y., and other similar institutions to study the effects of environmental factors on plant development, reproduction and other life processes. In such a study applied to plants the main factors considered are temperature, humidity and movement of air, carbon dioxide supply, light intensity and quality and day length. Most seed plants grow well within a temperature range of 6o to 8o° F but the optimum temperature for growth varies with the species. It may also vary with carbon dioxide supply and light intensity since it has been observed that many plants will grow more rapidly at a higher temperature when carbon dioxide supply and light intensity are both increased. A relative humidity of 5o to 8o% is favourable for many seed plants, but desert species exist in nature at a much lower humidity, and some aquatic plants live in a humidity which closely approximates com plete saturation. Many common crop plants will increase in growth rate and amount of carbon fixed when solar light intensity is high, if the concentration of carbon dioxide in the atmosphere is increased. The normal concentration is approximately three volumes of this gas in Io,000 of air, while the rate of photosyn thesis, or carbon fixation by green plants, increases at least up to Io times this concentration. This fact was first applied com mercially in Germany about 1917 when flue gases from the com bustion of coal or coke were purified and the resulting carbon dioxide piped into greenhouses among growing plants. This method has also been used in outdoor plots to increase the con centration of the gas locally over sugar beet fields and other grow ing crops. More recently pure charcoal briquettes have been burned in open stoves placed inside greenhouses, as a source for carbon dioxide. Increases of 500/0 or more in the green weight of plant tissue produced in a given time have been obtained in this way. The success of the method depends in part on light intensity since the plant uses the energy of light to synthesize carbohydrates from the carbon dioxide in the air and water, entering the plant from the soil. In the temperate zones during the winter months, light intensity is too low and day length too short for maximum photosynthesis of a number of plants. This can be overcome by the use of artificial light of a suitable intensity and quality for a few hours each night. Most seed plants grow well in greenhouses in the winter when daylight is supplemented with about six hours of artificial light each night. Longer light periods produce leaf injury or even death in a number of species. Many seed plants can be grown entirely with artificial light as a source of energy for photosynthesis. A room has been equipped for this work at the Boyce Thompson institute for plant research. This room is about II ft. square and is illuminated by 25 1,500-watt incandescent type gas-filled lamps arranged in the ceiling so as to give equal distribution of light over the floor area. A false ceiling of glass over which water can be circulated is placed between the lamps and the chamber in which the plants are grown. This serves as a ray filter which absorbs the infra red or heat rays from the lamps. Both temperature and humidity are controlled in this room by standard air conditioning machinery. The refrigeration unit used to cool water for this work has a capacity of 15 tons of ice per 24 hours. The air conditioning system has sufficient capacity to maintain any temperature between 45° and 90° F, accurately regu lated in the chamber under the bank of lamps. Carbon dioxide is delivered continuously into the growth chamber through a system of meters so as to maintain a concentration of about 3o parts in of air. The effects of temperature, humidity, light intensity, quality and day length, and carbon dioxide supply can be studied in such an artificial climate during the entire life history of the plant.
Many plants grow very rapidly in an artificial climate. Some of the grains such as spring wheat and oats were grown from seed to head in 3 5 days. Red clover, a biennial in the present system of agriculture, grew from seed to flower in 38 days. Illumination values of the order of 300-1,000-f oot candles are required for normal photosynthesis in plants. The light quality must be similar to sunlight, that is, it must contain both the red and blue regions of the spectrum. The gas-filled incandescent type of lamp is not an ideal source of light for plant growth, as it has too much red and infra red and insufficient blue. It has a distinct advan tage, however, in that it is easily maintained over long periods of time. It should be noted that day length is an important consid eration in the flowering of plants growing in artificial climates. As shown originally by Garner and Allard in 192o, some plants, such as the salvia and cosmos, flower on the short day lengths of fall, spring and winter. Other plants like the lettuce and radish, flower on the long days of summer. A third group, like the buck wheat, is not affected by day length and is, therefore, an ever blooming type. These considerations apply equally well when plants are grown under artificial illumination. Day lengths of 15 hours or less usually cause flowering in short day plants, while day lengths greater than this cause flowering only in long day plants or in the everblooming types.
To date there has been no practical application of the growth of plants solely with artificial light in a mechanically controlled environment. Artificial light has been used commercially to sup plement sunlight for a short time in forcing especially valuable flowers. With the advent of a more suitable light source and cheaper power, an application may be found in the future.
(J. M. A.) See also DAYLIGHT, ARTIFICIAL ; CLIMATE IN THE TREATMENT OF DISEASE ; HELIOTHERAPY.