1. What causes the mercury to sink in a barometer before a storm? 2. How do persons foretell the state of the weather from the movements of the barometer? 3. How far ahead can storms be predicted?
F. J. Elliott.
Answer.—The sinking of the mercury in the tube of a barometer is due to the lightness of the atmosphere, which is indicative, in most cases, of humidity, or aqueous vapor, in the air. The construction of a mercurial barometer may be stated in a few words. A glass tube, about 33 inches in length, open at one end, is filled with mercury, and while the unsealed end is covered, is inverted in a basin of mercury. As soon as the cover is removed the mercury in the tube will flow out until it stands about thirty inches above the mercury in the basin. At that point the pressure of the air upon the liquid in the basin is equal to the pressure of the liquid in the tube (the space in the upper part of the tube being a vacuum) and the flow ceases. When the air becomes heavier its pressure upon the basin will be greater and force the mercury in the tube higher; if the air becomes lighter the mercury in the tube will sink. The barometer therefore shows directly only the weight of the atmosphere, but thereby indirectly the future state of the weather is indicated. 2. This is explained in “Our Curiosity Shop” for 1881, pages 144-5. 3. How far ahead the changes of weather can be predicted depends upon so many other considerations besides that of the mere weight of the atmosphere, varying in different seasons of the year and different localities, that no answer suited to all can be given. In some instances storms have been predicted from observations of the barometer alone as much as thirty-six to forty hours before their arrival. The United States Signal Service bases its weather predictions not only on barometric phenomena, but on telegraphic reports from a multitude of stations of the temperature, humidity, clouds, direction, force and rate of motion of the winds, etc. In some cases it has given notice of storms starting in the Rocky Mountains and traveling eastward sixty hours before their arrival on the Atlantic seaboard.
EXEMPTIONS OF PRE-EMPTIONS AND HOMESTEADS.
Plankington, D. T.
Can a judgment rendered in Iowa eight or ten years ago attach to a pre-emption after the latter is proved and title taken from the government?
C. P. Wilton.
Answer.—It is expressly declared in the homestead law that “no lands acquired under the provisions of this chapter shall in any event become liable to the satisfaction of any debt contracted prior to the issuing of the patent therefor.” There is no such provision in the pre-emption law. Lands acquired under the latter law are protected from previous judgments only by the State or Territorial homestead and exemption laws.