1875.] 



671 



fBlasius, 



Chestnut street, the gas works above Market street, cemeteries, etc. 

 Any one who wants practical illustrations of the different effects of the 

 ' same air current on the western and eastern side of the Schuylkill, may 

 pay attention to his breathing before and after passing the Chestnut 

 street bridge. It is also a reason why the streets of a city should run from 

 southwest to northeast, and from northwest to southeast, in order that 

 during the warm season the prevailing currents could ventilate them and 

 change the poisonous air which generates in the sti'eets and yards. It is 

 probably the reason why in cities certain diseases become epidemic as it 

 enlarges, which before are comparatively unknown. 



How the direction and nature of prevailing air currents affect the 

 health of cities can be seen by comparing the rate of death in two suc- 

 cessive years, of which one brings quite a tropical, the other a more are- 

 tic climate, during summer. • This would seem to be due fully as much 

 to miasma as to the direct effects of the heat on the system. 



The Public Ledger of July 14, 1874, had an article comparing the 

 health of Philadelphia for the period June 15th to July 15th, of the years 

 1872, 1873 and 1874, in which the writer seems to ascribe the improvement 

 manifested to better aiTangements in city government. This of course 

 would have its effect, but the difference seems to me unquestionably due 

 in large part to the difference in the prevailing air-currents. 



From the data the Ledger article furnishes, I have compiled the follow- 

 ing comparison of mortality in the principal diseases, which is very strik- 

 ing in view of the fact that in June and July of 1872, the prevailing cur- 

 rents were from the southern semi-circle, and in the same time of 1874, 

 from the northern semi-circle : 



I have compared 1872 and 1874, because the contrast is strikingly 

 marked ; the mortality during the same weeks of 1873 was about midway 

 between, in conformity with the air-currents. 



The whole subject is of the greatest interest and the utmost import- 

 ance ; and the field of inquiry a very wide one, promising the most satis- 

 factory results. 



I have given these few suggestions merely to call attention to the sub- 

 ject. 



