460 



Dr. T. Carnelley and Mr. T. Wilson. 



From these experiments it is evident that Hesse's method is not 

 reliable for outside air, except when there is little or no wind. 



By reference to Table II it will be observed that, of the six 

 experiments made in outside air only two were concordant, the 

 discrepancy in the other four being very considerable. In order to 

 learn if this discrepancy was due to the effect of the wind, the state 

 of the latter was ascertained from the Observatory at the Dundee 

 Harbour, for all the dates on which experiments had been made in 

 outside air. The results were as follows : — 



Table IY. 



No. 



Direction 

 of 

 wind. 



Miles 

 per 

 hour. 



Wind as felt. 



Date. 



Micro- 

 organisms 

 in Hesse 



tube. 



Micro- 

 organisms 

 in flask. 



2 



S.W. 



7 



Little or none. 



April 22nd. 



3 



3 



3 



s. 



H 



Little or none. 



April 23rd. 



13 



12 



7 



S.W. to S. 



6 



Might be gusty. 



April 28th. 



47 



14 



9 



E. to N.E. 



11 



Steady. 



May 2nd. 



59 



26 



16 



W. to S.W. 



13i 



G-usty. 



May 19th. 



60 



11 



19 



W. to N.W. 



a* 



Gusty, 



May 21st. 



22 



5 



In the two cases in which the number of micro-organisms in the 

 flask corresponded with that in the tube, little or no wind was felt, 

 and the wind was travelling at the rate of about 6 miles per hour ; 

 whereas in the other four cases in which discordant results were 

 obtained, the wind was travelling at an average of about 10 miles per 

 hour, and was gusty besides. It would seem, therefore, that the 

 flask method gives more correct results than Hesse tubes for outside 

 air when there is any aerial disturbance. 



The only two cases in which there was any discrepancy for inside 

 air were Nos. 6 and 15. Both of these were samples of school air, 

 and it was noted at the time the samples were taken that in both 

 cases there was a considerable draught through the rooms, for the 

 day being warm, the windows and doors were all open. On com- 

 paring the determinations of carbonic acid made in these rooms at the 

 same time, it was found that in both they were comparatively very 

 low, viz., 10-6 vols, per 10,000 in No. 6, and 7 3 vols, in No. 15 ; 

 whereas average school air in Dundee contains about 19 vols, of car- 

 bonic acid per 10,000. This comparatively low amount of carbonic 

 acid can only be accounted for by the fact that there must have been 

 a draught in the room at the time the experiments were made. 



Experiments were also made in order to ascertain if any micro- 



