ANNIVERSARY ADDRESS. 9 
equal to eighteen, 64° prisms, while Colonel Campbell’s was 
only equivalent to eight. The measuring apparatus of mine 
also admits of measuring one three-hundredth part of the space 
between the D lines. In order to identify the lines I have 
numbered them 1 to 7, beginning at D1, and their positions as 
determined by a number of readings with the micrometer are as 
follows :— 
3 Saree 2 3 4 5 6 + a. DS 
000] 41] 67 | 124] 151 | 173 | 213 | 232 | 291 | 299 
4 is the nickel line always seen ; 7 is the position or very near it 
of the zine line; 1, 2, 3, 5, and 6 are evidently atmospheric 
lines, as they increased in distinctness very fast as the sun neared 
the horizon; 4 also seems to enlarge as if there were an atmo- 
spheric line coincident with it, and 6 increased faster than any 
other; when the sun was near the horizon it was as thick again 
as D1; 7 did not increase at all, and almost disappeared when 
the sun was near setting. 
The line D3 has not, I think, been described before. It is a 
difficult line to see, and only to be made out with high powers. 
I have not reduced my measures to wave lengths, because the 
results obtained by Dr. Huggins and Colonel Campbell are only 
recorded in drawings, without measures. I have’ had prepared 
enlarged drawings of those obtained in Oxford and London, 
with a careful plot from my own measures, which I now show 
you. 
There are not many of the lines which agree; but as Dr. 
Huggins used bisulphide of carbon prisms, and Colonel Campbell 
only eight prisms, some of the differences might disappear if all 
could be reduced to wave lengths. On closely comparing the 
drawings, it will be seen that five lines were recorded in London 
between my 7 and D 2, two others between D1 and No. 1, and 
three between Nos. 2 and 3. These spaces appear in Sydney, 
_ even under the most favourable conditions, entirely free from 
lines, or any sign of them. It would appear, therefore, that 
there must be some gases in the atmosphere of Europe, and 
