Page:Popular Science Monthly Volume 39.djvu/587

Rh introduced into the dado space at a low level and in a lateral direction to promote diffusion, through a number of inlets from the outer atmosphere along the whole line. The total area of these inlets is proportioned to the area of the hot-air shaft provided for carrying off the impure air. The total space inclosed by the dados is much greater than the total area of the inlets from the outer atmosphere; and by this means the entering air is made to spread itself slowly through the interior of the reservoir, and to percolate gently through the gauzes so as to permeate the atmosphere of the room by gentle diffusion, instead of entering in a stream. In winter the air admitted may be warmed by a heating surface of pipes fitted along the length of the dado. For carrying off the impure air, a chimney of suitable capacity is provided, with a close-throated fire grate; or a connection is formed with any existing perpendicular flue. There should be an opening in the room, at a high level, into an outlet tube communicating with the perpendicular column of rarefied air in the chimney or flue. When a suitable chimney or upright flue is not available, the same results are produced by a suitable tube erected above a skylight in the roof of the hall, in which a current may also be promoted by means of a Bunsen burner.

Labor as a Means of Human Improvement.—The remark which has been a long time current is re-enforced by the latest studies, that the prevailing and dominant people, races, or nations, and the flow of superior human energy have always come from the cold, bleak, inhospitable regions of the north. Notwithstanding physiology indicates a tropical or subtropical origin for mankind, man in the tropical regions makes no advance, but tends, on the whole, to decline; and when men from the temperate zone settle in tropical regions, they are very liable to become enervated. The probable reason for this tendency is that living in such regions is too easy, and that the conditions prevailing there do not afford the stimulus to the exertion without which it is impossible to keep up vigor. So, when, anywhere, a hard-working, active people meet with fortune and settle into a life of ease, they begin at once to weaken. In England, it is the common people who are multiplying rapidly and swarming all over the earth; while the aristocracy can not even keep up its stock, but has to be refreshed from time to time by the interpolation of fresh blood. These facts are used by Prof. Williams to enforce the maxim that every human being should earn his daily bread by daily work, and that the inheritance of such an amount of wealth as shall render a man or a woman a mere purposeless pleasure-seeker is a most degrading curse.

Aniline Photographs.—Analogous to the photographic process with the salts of silver is the production of pictures by a similar process with the aniline colors. As described by Messrs. Green, Cross, and Bevan, in the Society of Arts, the simplest method of producing a picture in any of these colors is based upon the fact that they all fade more or less on exposure to sunlight. Prints obtained by exposure to sunlight of paper coated with eosine and methylene blue were exhibited by the authors, in which the gradations of shade were exactly reproduced; those parts which received the most light were the most bleached, whereas the shadows of the object had protected the parts of the paper beneath them, and the depth of the shadow of the original was thereby reproduced. These pictures have no practical value, because they are destined to be obliterated by the gradual fading out of the whole surface. In the diazotype process, the picture is fixed by causing a compound to be formed which will resist the further action of the light. The process starts with the yellow body called primuline—a substance constituted with ammonia, having one of the hydrogen atoms replaced by a complex group. It combines with nitrous acid to form a diazo compound, and this, like the other diazo derivatives, exercises a constructive or synthetic reaction with the amines and phenols, with which azo-coloring matters are formed. The essential conditions of primuline photography are that the reactions take place with primuline after its application to any surface or material as a dye, without affecting its union with the material; and that the diazo derivative produces the photo-sensitive in the highest degree. The prints obtained are positive, the light and