ANNIVERSARY ADDRESS. — 47 
The comet, which is now visible in the morning sky, has, as 
you are aware, been photographed several times at the Sydney 
Observatory ; and these photographs bring to light wholly unex- 
pected phenomena in the comet’s tails—phenomena which are of 
great scientific importance, showing, as they do, that in the camera 
we have an instrument for analysing light presented to us by a 
chemical method, which will go hand-in-hand with the spectroscopic 
method, for by it we may make a first analysis of the light over 
a large surface preparatory to the application of the spectroscope, 
which only tests a minute portion at a time. The members will 
remember that in photographs of the nebula about Eta Argus 
exhibited here, the camera revealed a most complex structure in 
parts, which, to the eye, presented a nearly uniform light, and no 
sign of such structure. And the same action in the sensitive plate 
was pointed out in photographs of coloured stars. In those of the 
comet the same selective action is observed, and it has brought 
to light no less than eight ribbon-like rays in the tail of the comet, 
which otherwise would have remained unknown, but for the part 
photography has played, for in the part of the tail visible through 
the telescope no sign of these rays could be seen, even when I 
knew from the photograph that they were there, and were 
photographically brighter than the hazy part near the coma, 
They are then features invisible to the eye, but caught by the 
sensitive plate—or, to put it in another way, we have a comet 
with coloured rays in its tail, rays which are probably blue or 
violet, from the fact that in comet spectra blue light prevails ; 
and therefore, the sensitive plate, by its selective power, as well 
as by its power of storing up faint rays, may be used to make a 
preliminary analysis of cometary or nebulous light, and point the 
way for the more searching investigation with the spectroscope. 
Ocean Currents.—For several years past the Observatory has 
kept up, for all who would assist in the work, a “current paper ” 
department, and printed papers have been freely supplied to com- 
manders of vessels and others, and quite a number of papers have 
been returned found upon our coast and in various parts of the 
