502 



SCIENCE. 



[Vol. I., No. 18. 



when the results of scientific investigations are 

 used as a medium for Immor, their true objects 

 are, of course, entirely lost sight of, and sci- 

 ence is belittled ; and, as humor appeals to the 

 greater number the lower its order, it is clear 

 that the kind of humor we are dealing with 

 must appeal to large numbers of those who 

 are in special need of enlightenment. 



Scientific investigations are not proper sub- 

 jects for the display of wit. The object of 

 these investigations is to discover the founda- 

 tion of all things, — the truth. Let a man 

 once grasp that idea, let him become imbued 

 with it, let him go through the process of in- 

 tellectual regeneration necessarj- to enable him 

 fullj' to appreciate it, and it will henceforth be 

 impossible for him to touch upon the subject 

 of investigation without experiencing feelings 

 which are totally incompatible with ordinary 

 wit. This is the right attitude towards scien- 

 tific matters. It cannot be brought about all 

 at once, but the day when it shall be the gen- 

 eral attitude can be hastened by those who 

 mould public opinion. 



Gentlemen of the press, it is your duty to 

 do all in jour power to encourage scientific 

 work, and to give the people right ideas con- 

 cerning it. We cannot expect this from all. 

 There are many among you whose highest 

 ambition it is to secure and construct ' reada- 

 ble ' articles at any sacrifice of principle. But 

 surelj' it is not too much to expect of those 

 who evidently recognize the importance of 

 higher things. 



THE DRY- AND WET -BULB HYGROM- 

 ETER.^ 



It is not mj' purpose at present to discuss 

 the theories which underlie hygrometric obser- 

 vations, but rather to ascertain if it is possible 

 to obtain uniform and trustworthy- results from 

 the simple observation of this instrument. 

 There has been much discussion of late upon 

 this subject, and grave doubts are continuallj^ 

 being thrown upon its accuracj'. 



It is proposed to ascertain, first, the best 

 method of conducting observations, and, sec- 

 ond, the accuracy of the results when comjjared 



1 Read before the Philosophical society of Washington, D.C., 

 May 6, 1883, at its 236th meeting. 



with a fixed standard. The following is a brief 

 statement of the principles upon which the 

 action of this instrument is based : — 



" The evapoi'ation of a liquid involves the 

 conversion of sensible into latent heat ; and the 

 supply of heat must be drawn from the liquid 

 or from surrounding objects. At some point 

 the amounts of heat subtracted and communi- 

 cated will be equal, and an invariable tempera- 

 ture of evaporation will result, depending upon 

 the amount of moisture present." 



From this invariable temperature we maj^ be 

 able, b}- suitable formulae, to obtain the hj-gro- 

 metric state of the atmosphere. 



It would seem as though a thermometer- 

 bulb, from which moisture is continuously 

 evaporated, ought to give this needed temper- 

 ature ; yet everj- one who has had occasion to 

 make such observations has encountered great 

 difHculties, and has become satisfied, that as 

 commonlj' made, though the readings are of the 

 simplest character, yet the results are frequently 

 entirely inaccurate. This is partially shown 

 bj- aii examination of the various directions 

 that have been published from time to time. 

 Regnault, writing in 1845, says, " I prefer ther- 

 mometers with cylindrical bulbs as more sus- 

 ceptible to the variations of temperature, and 

 because, for the same mass of mercury, they 

 present a much, greater surface to the air. 

 The manner of moistening, I find, makes no 

 difference so long as there is an abundance of 

 liquid. If a drop falls fi'om time to time from 

 the extremitj- of the bulb, I have still observed 

 no sensible difference. The longer or shorter 

 course which the water runs on the cotton wick 

 exercised no perceptible influence." Other 

 authorities maj- be quoted as follows : — 



Bulbs of both thermometers should project 

 an inch and a half to two inches below the 

 scales ; and all objects, metallic or otherwise, 

 wliich can affect the temperature, should be re- 

 moved.^ 



All authorities mention the necessity of using 

 rain or distilled water, of frequent cleansing of 

 the muslin, and of changing it at intervals 

 of from half a month to three months. The 

 greatest difference of opinion, however, is in 

 relation to observations below freezing, ' under 

 which cii'cumstances,' sajs Mr. Scott in his 



' This is an important matter. I liave seen several illustra- 

 tions of this instrument, showins the scales extendim; below the 

 thermometer-bulb; and many otherwise accurate thermometers 

 are made with a metallic scale piolonged so as to att'ord protec- 

 tion to the bulb. In using such a thci-momcter as a wet bulb, I 

 have found, with the scale, a mean temperature 1.2° higher than 

 ■without it; the air was still ; there was an abundance of moisture, 

 and over 10° difference between the dry and the wet. This is 

 due partly to the heat radiated from so near an approach of metal 

 at least 10° hotter than the wet bulb, and partly to the arrest 

 of evaporation by the scale. 



