24 MR JOHN ATTKEN ON 



on gases in the atmosphere is : after they are formed, do they remain active for any 

 length of time, or are they short-lived ? Unfortunately, for reasons already given, 

 this point has not been thoroughly worked out ; but this much has been ascer- 

 tained: some of them, such as the hydrogen peroxide nuclei, arc very short-lived — 

 fifteen minutes to half-an-hour being sufficient for the air in the flask to lose its 

 power of cloudy condensation ; whilst the nuclei from sulphurous acid remain active 

 for a long time, half an hour having no appreciable effect on the density of the 

 condensation when that substance forms the nuclei. In this case the nuclei are 

 probably particles of fine sulphur dust, and their action seems to be as permanent as 

 that of ordinary atmospheric dust. 



As might be expected, all the gases do not respond to light rays of the same rate 

 of vibration ; but no extensive experiments have been made in this direction. It may, 

 however, be mentioned that whilst sulphurous acid is easily made active by means of 

 the light of burning magnesium, on many of the other gases that light has little if any 

 action. The action of burning magnesium on sulphurous acid makes a convenient 

 lecture experiment, the flask being shown free from cloudy condensation when the moist 

 air and sulphurous acid vapour are expanded, if the room be lit with gas. On now 

 burning two or three inches of magnesium ribbon, and expanding, the air in the flask 

 becomes densely white with cloudy condensation. 



Whilst these experiments show that many gases which are frequently found in the 

 atmosphere form nuclei of condensation after being acted on by sunlight, yet it must 

 be admitted that they throw but little light on the abnormally high dust readings got 

 at Kingairloch, when the wind blew from a pure direction and the sun shone. On 

 looking for a source of impurities in the atmosphere at Kingairloch, I found there 

 was a " mineral well" to the north-west of the place of observation, at a distance of 

 about three miles ; and on inquiry I found that there are a number of these wells in the 

 district. The water in these wells contains sulphuretted hydrogen, and it seemed 

 possible that this gas under the action of sunlight might be the cause of the abnormal 

 number of nuclei ; but as yet I have not been able to get evidence sufficient to bring- 

 in a verdict against it. Since I discovered that the sunlight was in some way 

 connected with the production of these nuclei of condensation in N.W. winds, I have 

 only been once at Kingairloch to test if the mineral springs supplied the gas out of 

 which the nuclei were produced, but unfortunately the weather was never favourable 

 for a test. If the sun shone, the wind was in the wrong direction, and when the wind 

 was N.W., there was no sunshine. Only on one day did I get a minute or two of weak 

 sunshine while the wind was N.W., but on that occasion I got no evidence against the 

 well. The numbers were the same in the air coming to the well as in the air leaving 

 it. The test, however, was too imperfect to put any reliance on, as by the time I got 

 to a small distance to the lee side of the well, to get the air after the sun had time to 

 act on it, the sun was under a cloud. I have also had some of the water bottled and 

 brought here, where it was tested by placing some of it in the test-flask, and sunning 



