1859.] on the Estimation of the Organic Matter of the Air. 93 



of this to be that a drier air does not allow the offensive matter to rise 

 so readily. This fact has many ramifications, but it will explain 

 several difficulties in our sanitary science. It is with the assistance of 

 moisture that the organic matter is conveyed into the air. 



Moisture itself, as may be supposed, does not produce any action 

 on the test ; one of the lowest numbers obtained was on the German 

 Ocean, about 60 miles from land ; the day was calm and clear. In 

 the straits of Dover, when the wind was blowing briskly from the 

 German Sea, the amount obtained was very high, but as there was a 

 slight spray the experiments were disregarded. About 8000 feet high 

 on the Alps, a dense fog showed also one of the smallest amounts 

 obtained ; the ground was entirely bare rock, and could not give out 

 organic matter. The amount was 2 • 8. 



The influence of height was very decided. In the higher grounds 

 of Lancashire, near Preston, the numbers being from 2 to 4. A wind 

 blowing down from the Mer de Glace gave rather more than at a 

 lower point, although coming down the hill ; a dry pine forest in the 

 neighbourhood, although very fragrant, did not appear to raise the num- 

 ber. The influence of the sea and of height seem equally decided. 



A few hasty experiments made in the hothouses at Kew led me to 

 believe that there was less increase there than might have been ex- 

 pected, the amounts obtained being less than in London, but more than 

 outside the houses, where it was cooler. At the same time weeks 

 or months should be given, when only hours were allowed for the 

 experiments. 



The influence of heat appears to be to increase the amount, when 

 there is moisture present. 



The influence of dryness seems to be towards diminishing the 

 amount. 



The influence of great cold has not been tried yet. 



The influence of rain in hot weather, to some extent of course a 

 cooling influence but chiefly a means of washing the air, seems most 

 decided. After a thunderstorm and shower at Camden-square, the 

 number, which was previously 31, fell to 12. 



The influence of our towns, especially our smoky towns, is most 

 decided also ; it is easy to tell by this test, when in the outskirts of a 

 town, whether the wind is blowing from the town or the country. 



A distinct difference was always found between the front and back 

 of Manchester houses : a similar difference obtained when a room had 

 been inhabited for some time, and the difference was of course very 

 marked when the smell of a sewer came into the house. I had a good 

 opportunity of observing this in my laboratory last year. 



It must be remembered that the numbers given for some places 

 were obtained on one day of the year only, and we must be careful not to 

 draw too many conclusions : we have yet to learn what kind of organic 

 matter is wholesome and what is unwholesome. I believe that this is 

 the next great point to be attended to ; at present we are only be- 

 coming able to ascertain the gross amount. I feel this caution to be 

 needful, lest the numbers should be used to prove too much. 



