Page:Popular Science Monthly Volume 10.djvu/525

Rh had rooms in the Cooper Union Building, but from the beginning it has been the intention of the leading members to secure possession of a building large enough to receive their valuable collection and library. The new headquarters is a large four-story and basement brown-stone front house on Twenty-ninth Street, near Fifth Avenue. On the first floor is a spacious reception-room, extending the entire depth of the house; its walls are covered with maps and charts. One of the curiosities of this room is the large map of South America once used by Humboldt. On this floor is also the room of the president of the Society. The second floor is devoted to the library and the secretary's room. In the library are 20,000 volumes, classified according to countries. The third floor contains the collection of maps and atlases. On the fourth floor is the Council's room, and in the basement are the offices for the clerical force.

On the evening of November 29th a second reception was held by the Society, and a paper on a journey to the Spitzbergen Sea was read by A. H. v. d. Hoeck. The author took occasion to expatiate upon the value of arctic research, pointing out the important results thence to be derived for anthropology, zoölogy, geology and paleontology, physics, and meteorology. Manuel M. Pereira, minister resident of Costa Rica, read a short paper on the projected canal across the Isthmus of Darien.

Hygrometers.—An hygrometer is an instrument for measuring the moisture of the atmosphere. It is often useful for gauging the dryness of rooms. It may not be generally known how simply such an instrument may be constructed.

When water, by means of a moist rag (whose moisture may be kept up by contact with water in a saucer or teacup), is spread over the surface of the bulb of a thermometer, the mercury in the latter falls, generally several degrees. The reason is, that the water evaporates and cools the bulb. The evaporation which takes place is, of course, produced by the absorption of heat from surrounding objects, the bulb included. The thermometer is affected in proportion to the reduction of temperature caused by the evaporation. It is evident that just as much heat as is required to convert water into vapor, just so much cold (or deprivation of heat) will be required to convert the vapor back again into water. When vapor begins to condense into water the temperature is at what is called the dew-point. It is evident, therefore, that theoretically the dew-point is twice as far as the vapor-point below the normal temperature of the atmosphere. Experiments show that it is a little more; a constant quantity of 1° Fahr. having to be added for heat lost and dissipated in the process.

These facts may be exemplified as follows: Hang two thermometers in a room of equable temperature, and suspend a third in a tin or glass vessel containing some tepid water. Wet the bulb of thermometer No. 2 as suggested above, and the evaporation will show the vapor-point. Pour ice water gradually and slowly into the vessel containing No. 3, and mingle it well with the water already there until the whole becomes so cold that the exterior of the vessel begins to contract moisture. It is then at the dew-point, and the thermometer in the vessel will be found to have fallen twice as much as No. 2, and 1° more.

No. 2 is a perfect hygrometer, as it shows the relative dampness of the atmosphere. When the latter is very dry, as in a room warmed by a hot-air furnace, evaporation takes place rapidly, and a large quantity of heat is abstracted from the bulb. When moist, as during a shower, very little evaporation takes place, and there is but a slight fall of the hygrometer. When the atmosphere is too dry the lungs suffer. It is in a wholesome condition when the hygrometer does not fall more than 7° Fahr. below the normal temperature. A hot-air furnace often sends it down 10° or 12° below.

The Studies of an Engineer.—Prof. Reynolds, of Owens College, Manchester, in an address on "Engineering as a Profession," proposes the following course of preparation for the student who aims to be an engineer: Up to the age of sixteen or seventeen he should devote himself to acquiring a "general education." Then he enters on his special course. In this he must learn something of science and something of art;