436 TRANSACtlONS OF THE AMERICAN INSTITUTE. 



of this kind, the degree of atmospheric saturation at the time of an observa- 

 tion may be calculated. Suppose the teiiT^jeratuve of the air is at 80 deg". 

 Fah., and the dew-point, that is, the point at which the air is saturat,ed and 

 dew begins to be formed is 10 deg'., and that the saturating point .at 80 

 deg. be called 1000. Then as the quantity of vapor is directly as the ten- 

 sion, we have by proportion — 1.0221 : 0.1321 : : 1000 : ^, or ,t=116. 



Practically, however, it is easier to find the dew point by oieasuring the 

 rate of evaporation at the time of the observation of tempei^ature. This is 

 done by means of the wet bulb hygrometer, which consists of two ther- 

 mometers, both of which are covered with muslin and one is kept constantly 

 moist by means of capillary attraction — a few cotton fibers being connected 

 with the muslin and water in a separate vessel. The rate of evaporation 

 and consequejitly the depression of temperature of the moistened bulb will 

 be greater in proportion as the atmosphere is further removed from its 

 point of saturation. By means of prepared tables the dew point is calcu- 

 lated from these observations. 



The gentleman to address us this evening is a man of great experience, 

 having reached his seventy-eighth year. He has for more than thirty years 

 made regular meteorological observations, and he is one of the valuable 

 corps of observers who furnish reports of the weather for the Smithsonian 

 Institute at Washington. His views may be regarded by some as ultra, 

 but they will doubtless have the effect of directing our attention to really 

 important points which have hitherto been overlooked. 



Prof. Baer remarked, — There was no law in nature v/hich is more impor- 

 tant than that belonging to the dew point. What is meant by the dew 

 point is the relative amount of water, or moisture, in the atmosphere. No 

 manufacturer of iron can make a uniform quality without taking into con- 

 sideration the dew point; in fact evei-y branch of manufacture is affected 

 by it. Oxygen being a supporter of life, it becomes necessary that we 

 should know its purity, that is when the atoms of the air which consists of 

 oxygen and nitrogen in the proportion of about 21 volumes of oxygen to 19 

 of nitrogen. When these g-ases are disseminated, or fill up the interstices 

 of vapor, of water, in breathing which a large amount of vapor is taken 

 into the lungs that requires considerable effort w the system to get rid of, 

 and air thus saturated with moisture is rendered impure. And in the case 

 of the bloom-maker or blacksmith who wishes to make iron of a certain 

 quality, and as a certain amount of oxygen is required for the f?res, a south- 

 east wind coming up laden with moisture, and which holds the oxygen in 

 solution,' a very great amount of heat will be needed to get this oxygen 

 out of the moist atmosphere; and a No. 1 iron cannot be made ; it wiil 

 range somewhere about the quality of No. 4, or grey iron. As no more air 

 than the bellows is capable of furnishing can pass into the lire; and this 

 air being largely saturated with moisture which a large part of the heat is 

 employed in dispelling, an irtdifiei'ent "quality of iron will necessarily be the 

 result. We see here how important the d(^w point becomes in this exten- 

 sive branch of manufacture. He had watched this matter very closely 

 where he lived, as the "iron furnaces were about a mile from his residence. 

 He found that the month of June is generally a time when the dew point 

 is high, and during that month three bellows are required where with a 



