220 ANNUAL OF SCIENTIFIC DISCOVERY. 



thence occasionally down to the 20th of July. They were accompanied 

 by notes of the barometer, the temperature, and the direction and force 

 of the wind. Among the results obtained were the following, as briefly 

 given by Prof. H. 



That, other things being equal, the moisture is in general propor- 

 tioned to the temperature ; that slight variations of temperature are not 

 accompanied by corresponding variations in the quantity of moisture, 

 and that great variations in the quantity of moisture may take place, 

 while the temperature and altitude of the mercurial column remain 

 constant. The quantity of the moisture, too, has even doubled in the 

 course of an hour, although the temperature became reduced. In 

 general, again, the moisture on the same day seems to depend chiefly on 

 the direction of the wind. 



The least quantity of moisture was observed during a northwest or 

 north-northwest wind ; the largest, during a southwest or south-south- 

 west wind. The former occurred on the 12th of March, and the latter on 

 the 23d of June last. The quantity on the latter day was to that on the 

 former as more than fifty to one. 



The method employed was that of Brunner, which consists of an appa- 

 ratus for transmitting a known volume of atmospheric air through 

 a chloride-of-calcium tube, previously and subsequently weighed. The 

 difference between the weights before and after the experiment presents 

 the amount of moisture in a given volume of air. 



The permeability of atmospheric air to aqueous vapor was established 

 by experiment, and the observations extended through a period of several 

 months. It has been observed, that the striking through of ink emploijed 

 in writing takes place more promptly in very hot than in cooler weather. 

 A piece of writing paper of known superficial area was placed in a glass 

 tube closed at one end, and weighed from day to day, noting at the same 

 time the temperature. It was found to weigh more as the temperature 

 was higher. 



The quantity of ammonia in the air was determined by an appara- 

 tus of the author's construction. The object in view in the arrange- 

 ment of the apparatus was. to provide that the air should, by means 

 of an aspirator, be transmitted through a constantly renewed at- 

 mosphere of hydrochloric acid vapor. To this end, a series of tubes 

 and flasks containing asbestos drenched with hydrochloric acid were 

 connected with a safety-tube, which was connected with an aspirator. 

 Through this apparatus a known volume of air was transmitted. At 

 the conclusion of the experiment, the apparatus was thoroughly rinsed 

 with distilled water, and the ammonia determined in the usual manner 

 with bichloride of platinum. Several determinations having been 

 made, it was ascertained that the quantities of ammonia in the east 

 loind varied considerably from each other; and such was the discrep- 

 ancy of the Professor's results that he forbore a statement of quanti- 

 ties ascertained, except so far as to remark, that they very greatly 

 exceed those obtained by Fresenius in his recent determinations. One 

 determination was made in a locality in Boston pointed out by one of 

 the police-officers as the worst habitable part of the city, and the at- 

 mosphere, which was in the highest degree offensive, was not found to 



