15B Methods of fokecasting the weather. 



make .sure that the weather scale is correctly fixed on it. The makers 

 of these instruments must know the mean pressure at the dwelling- 

 place of the purchaser; there they place the term "changeable;" the 

 point where the pressure is about 10 millimeters above the mean is 

 " line," and at about 20 millimeters above the point designated as 

 "changeable" will be "steady," "fine," or "dry," or the like, kt 

 about the same distance below "changeable" is placed "rain" and 

 "storm." 



Whoever has provided himself with an instrument of this kind 

 believes himself to l)e the possessor of a self -registering weather 

 prophet and is generally highly indignant if it rains when his barome- 

 ter stands at "fine," or astonished if it is fine weather when the barom- 

 eter says." rain." Since these erroneous indications are not unusual 

 with the barometer, therefore faith in it as an indicator of the weather 

 is very much diminished, and is only maintained at all, on the one 

 hand, by the fact that the barometer frequently "indicates correctly," 

 and, on the other hand, by force of habit. Frequently, however, one 

 has taken refuge in another instrument, namely, the hygrometer. 

 This instrument shows only the amount of moisture actually prevail- 

 ing in the air, in the same way that the barometer indicates the act- 

 ually prevailing- pressure. As the pressure and the moisture are both 

 connected with the weather, the hygrometer may be used as a weather 

 prophet in the same way as the barometer, although that is not its real 

 vocation. If the h3'grometer shows a high degree of moisture, that 

 only indicates that the air is just then very moist, and this generall}' 

 happens onl}^ when the weather is already bad. However, it happens 

 sometimes that the moisture in the air increases while the weather is 

 still fine, so that the hygrometer then indicates approaching ])ad 

 weather. In the same way, the hygrometer will generally indicate 

 dryness when the weather is fine; it will sometimes, however, when 

 the weather is not j^et fine, point to decreasing moisture, and there))y 

 foretell approaching drier and finer weather. The best of these 

 hj^grometers are made of human hairs, divested of grease, which have 

 the property of being expanded by dampness and contracted by dry- 

 ness in a most admirable manner. This property of varying its dimen- 

 sions with the changing moisture is also possessed, by other animal 

 and vegetable substances. There are a number of weather indicators 

 of this kind, among which the little house with the little man and 

 woman, in which the man goes out in bad weather and the woman in 

 fine w^eather, is probably the best known. 



The discredit into which the hygrometer as a weather prophet has 

 often faHen is as easily understood as in the case of the barometer. 

 Its duty is only to show the moisture actually prevailing at its locality, 

 and this knowledge does not enable one to make determinations of the 

 approaching weather any more accurately than does a knowledge of 

 the pressure at any place. 



