233 
1916-17.] On some Nuclei of Cloudy Condensation. 
If, however, two or three minutes were allowed for the nuclei to collect, 
there was a dense fog with the slightest supersaturation, requiring filtered 
air to be added before testing, when it was found that almost all the 
nuclei were large. It looks as if the particles coagulate and grow in size 
when they are in sufficient numbers and time is given for the action ; the 
aggregation of the nuclei to form large ones is probably assisted by the 
great number of ions produced by the oxidising phosphorus. The very 
small particles first formed are very short-lived, their electric charges 
possibly causing them to adhere to each other or to the walls of the flask ; 
but the large ones remain many hours, possibly because of the ions having 
neutralised each other. 
Aluminium, Magnesium, Zinc, and Lead. 
Inquiry was now made to see if any metals produced nuclei while 
oxidising at ordinary temperatures, in the same way as they do at high 
temperatures, the ordinary metals which have the power of displacing 
hydrogen being selected. Aluminium, which is generally supposed to oxi- 
dise rapidly at first though slowly afterwards, was first tested. 50 cm. 
of aluminium wire 1*6 mm. thick was polished with emery and wound 
into a spiral form, care being taken to touch it as little as possible. The 
wire was then introduced into the flask V and the apparatus filled with 
filtered air. After resting a time the air was drawn into the test-flask, but 
extremely few nuclei were found, and all required very high expansions. 
Magnesium was next tested in dry air, and found to be much more 
nucleus-producing than aluminium. 15 cm. of magnesium ribbon was 
polished, wound into a spiral, and hung in the flask V. After being 
pumped clear it was left for half an hour. On testing, a number of 
showers were obtained (see test No. 10, Table III). As will be seen, there 
were no large particles ; the greater number of them responded to an ex- 
pansion at 10 per cent. In some other tests the numbers were greater and 
the particles larger. The conditions were now changed, as it was thought 
that the moisture in the air might probably be the oxidising agent. A 
few drops of water were put in the flask along with the magnesium to 
moisten the air. On testing after thirty minutes’ action, a great increase 
both in the size, and the number was found (see test No. 11). By com- 
paring the figures in this test with the result of the tests of the air at 
Falkirk (Table II), it will be seen that about twice as many particles were 
produced by it as were observed in the polluted air of the place named. 
„A test was also made of the effect of the action of magnesium for only 
two minutes, and the result is given in test No. 12, Table III, from which 
