OPTICAL INSTRUMENTS AND SILVERING GLASS SURFACES. 421 
instruments. Iam sire it would have been a great blessing to many 
previous observers, where the difficulty of getting sufficient accommo- 
dation in the way of huts, in heavy rains especially, was sometimes 
very great. I do not know whether everyone understands the principle 
of the instrument, but if not I shall be very pleased to explain it 
further. I consider it is one of the most uscful instruments for a 
certain kind of work; even in a fixed observatory, if a man has a 
branch of work that lies in a certain zone, he can practically fix his 
telescope and go on making observations night after night with the 
certainty that he is working under the most favourable conditions 
possible. I think that these three instruments, which I have brought 
to your notice, and more particularly this ccelostat, are tremendously 
great advances in the way of astronomical instruments. I think the 
last certainly has a great future before it, because there are so many 
classes of work that it is capable of doing; and, as I say, for eclipse 
work it is simply admirable. 
To return to the silvering :—None of these solutions are working 
quite as I should like them, but that as you know is generally the way. 
This mirror has not a thick deposit of nitrate upon it, though it is a 
very fine illustration of the coating that it is necessary to put on to 
an object glass or otherwise to reduce the glare of the sun, it is not a 
specimen of the film one ought to have on an astronomical mirror or 
plane. The solutions in this bottle are not working very satisfactorily. 
This long tube, however, is much better and shews what can be done 
fairly well. Like all empirical processes, it is not a certain one, but as 
a rule when you have done it a few times you can get absolute success. 
I have given an appendix with a few notes written some time ago 
about silvering, together with an additional note, from which any one 
can with a little care be sure of success. 
I should like to say a few words about the eclipse, which I referred 
to just now, in case anybody should care to take the opportunity, 
which will be given by this eclipse, and not again for many years to 
those living in England, to take a short sea trip and see it. The 
eclipse begins just to the north-east of Scotland, at sunrise, and the 
further you get east the higher the sun will be up. It will be well 
seen at Bédo, which as you know is on the west side of Norway and 
not very far up the coast beyond Trondhjem; this no doubt would be 
a very charming trip. I had occasion to go to Bodo some five or six 
years ago and I cannot imagine a more delightful sail, especially to 
bad sailors, (for there is no doubt that some people’s pleasure is very 
much sacrificed in that way when they suffer from sea-sickness), as 
once across the German ocean, the steamers go up what is called the 
inner lead among the little islands that stretch along the west side of 
Norway. ‘The eclipse will be visible from just a little south of Bodo 
and at other points on the west coast, but not under the best 
conditions, as the sun is not very high, only some 7° or 8°, but still, 
except for scientific work, sufficiently high to enable a good run; and 
as many of us have never seen a total solar eclipse and never will again, 
it is an opportunity not to be lost sight of. By going round the 
North Cape and passing into the Varanger Fiord, as I am going (and 
