SERIES XIV.

3

6

T0056 sec.

9

graph as that of Series X. Fig. 6. My experience is that most persons pronounce what they have seen to be a regular and symmetrical star-shaped figure, and they are surprised when they come to examine it by detail in continuous light to find how far this is from the truth. Especially is this the case if no irregularity is suspected beforehand. I believe that the observer, usually finding himself unable to attend to more than a portion of the rays in the system, is liable instinctively to pick out for attention a part of the circumference where they are regularly spaced, and to fill up the rest in imagination, and that where a ray may be really absent he prefers to consider that it has been imperfectly viewed.

This opinion is confirmed by the fact that in several cases I have been able to observe with the naked eye a splash that was also simultaneously photographed, and have made the memorandum "quite regular," though the photograph subsequently showed irregularity. It must, however, be observed that the absolute darkness and other conditions necessary for photography are not very favourable for direct vision.

And now my tale is told, or rather as much of it as the limits of the time allowed me will permit. I think you will agree that the phenomena are very beautiful, and that the details of this transaction, familiar though it has been to all mankind since the world began, have yet proved worthy of an hour's attention.

[A. M. W.]

WEEKLY EVENING MEETING,

Friday, May 25, 1894.

WILLIAM HUGGINS, Esq. D.C.L. LL.D. F.R.S. Vice-President, in the Chair.

SIR HOWARD Grubb, F.R.S. F.R.A.S.

The Development of the Astronomical Telescope.

SINCE I last had the honour of lecturing in this theatre, astronomical research has had opened up to it a totally new field of work, one which appears almost without limit in its scope.

When Dr. Gill, of the Cape of Good Hope Observatory, made arrangements to photograph the comet of 1882 with a long exposure, using only an ordinary photographic lens, even his fertile and sanguine spirit did not, I think, anticipate the possibilities opened to astronomical research since photography has been called in to its aid.

I do not propose in this lecture to discuss any of the interesting astronomical and physical problems that have been opened up by the adoption of the "New Astronomy," as it is aptly called. I leave these subjects to be dealt with by those who have made such their special study, and are better qualified to speak of them.

I propose to-night to discuss the differing conditions which astronomical instruments are required to fulfil under the new system as compared with the old, and to point out the possibilities that appear to exist for improvement and future development, touching only on the astronomical part of the work so much as may be necessary to explain the instrumental equipment required.

It would be well, perhaps, that I should first call to your recollection some of the chief lines of work which have been opened by the introduction of the new photographic method.

The International Photographic Survey of the Heavens has been undertaken by sixteen of the principal observatories of the world, which have agreed to co-operate in producing two series of photographic pictures of the entire heavens; the first series including all stars down to the 11th magnitude, a catalogue of which is to be formed from the photographic plates; while the other series will include all stars to the 14th magnitude, and will be photographically reproduced as a chart.

The enormous advantages of photography for this work, as compared with the old system, have been brought so often and so prominently before you by Dr. Gill and other lecturers that it is unnecessary for me to dwell upon them here. As a supplement to