PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 441 



that but one pound per square inch pressure was lost by this plan. If tlic 

 pipe were made still larger there would be less loss of pressure, although 

 there might be a great loss of heat. ' 



A Four Legged Hen. 



Dr. Rowell exhibited a lusui^ natnrcc jn the form of a live hen having four 

 legs. T!ie pair of legs not used were nearly full size, and were drawn up 

 under the tail uf the animal. This freak of nature wasadouhtless the pro- 

 duct of a 'double yolked egg. It is said to be tlie general habit of the hen ■ 

 to throw out of the nest eggs of this description. 



The regular subject for discussion Avas then taken up. 



The Cause of the Impurity of our City Atmosphere. 



The Chairman said those present were doubtless aware that we were 

 often annoyed by a noxious odor or stench which passes away as suddenly 

 as it comes. Prof. Mapes had informed him that the cause did not originate 

 in the sewers, for he had taken pains to examine the openings to thenj 

 during the time the stench was strongest, and detected no odor arising 

 from that quarter; He had noted the position of the wind vanes visible 

 from his residence in Bleecker street, and had found that during the prdva- 

 lence of these odors the vanes always pointed in a northeast direction, or 

 in other words towards the gas works situated on tlie East river. 



Dr. Rich thought it impossible that the stench should arise from the 

 sewers. Prof. Everett had informed him that when certain changes \>ere 

 made in the gas works in the night tliis odor came so strong into his sum- 

 mer residence up town, that he was compelled to get up and close the 

 windows. 



Mr. Charles A. Seelye said this question of odors was well understood 

 up town. The stench from the gas works was quite distinct from that 

 arising from the bone boiling establishments. There is angtiier kind of 

 odor prevalent down town which is generated by decaj-ed vegetable matter. 



Gen. Hall said he had noticed that in the part of the city where the odor 

 comphiined of is the strongest, the children are remarkably plump and 

 healthy. , , 



Dr. D. D. Parmclce remarked that he had been, formerly, engaged in the 

 manufacture of a chemical coujpound which required the generatien of large 

 quantities of the unpleasant smelling gas coming from gas factories, but nio 

 complaint was ever made by his neighbors because he caused all the gas to be 

 absorbed by water, lime and other means. On Murray hill, where he livedo 

 he and his neighbors weYe obliged to stop using illuminating gas on account 

 of the sulphuretted hydrogen in it. 



Gen. Hall said thia might be accounted for by the fapt that the new com- 

 pany supply families abo^'e Thirty-fourth street, and they are not as success- 

 ful as the old donqmnies in arresting and destroying the gas complained of. 



The Chairman presented to the audience on the black board albthc formula 

 representing the impurities found in common air. Our atmosphere is called 

 a mixture of gases and not a true chemical compound. The great mass of it 

 consists of about four parts of nitrogen to one part of oxygen, by measure or 

 bulk. The water present varies in quantity with the temperature of the air. 



