pe ee 
7 pRAR, 
fi, Ae Fe eS 
4 
Scr 21 1896 
U wf 
ae \\ 
SS PATENT OF§ 
A417 
OPTICAL INSTRUMENTS AND SILVERING GLASS SURFACES. 
BY 
IDI, Ay, AVS COMO OWN, Il... lI. S. 
(President Royal Astronomical Society.) 
(A Lecture delivered at the Royal Artillery Institution, Woolwich, Thursday, 13th February, 1896.) 
Cotonet H. 8. 8. Warkrn, C.B., R.A., In THe Carr. 
Tare CoarrmMan—Let me introduce to you Dr. Common, President of 
the Royal Astronomical Society, whose work in connection with 
astronomy generally, and especially with one branch of it, stellar 
photography, is so well known, and who has kindly consented to 
give us a lecture ona subject which, I think, should be very interesting 
tous as gunners. From the time we are cadets to the time when we 
are full fledged gunners we have to deal with optical instruments of 
some kind or other—from the humble opera glass to the more com- 
plicated telescopic sights, range-finders, or position-finders, and I 
cannot help thinking that armed science will be greatly indebted to 
Dr. Common for his lecture this evening—(applause.) 
Dr. Common—Colonel Watkin, ladies and gentlemen, the lecture 
which I propose to give you to-night divides itself into two heads, 
optical instruments and the silvering of glass mirrors. I will not stop 
at the present time to tell you how this title came about, but I feel 
that the first part of it is rather misleading. I meant to speak of a 
point that in my eyes is of great importance, that is, the care of optical 
instruments and the adjustment of them; but I found it was such a 
large subject to treat properly that I was very glad to find the title 
cut down to optical instruments only ; and, that you may know what 
you may expect, I will just mention that all the optical instruments 
that I am going to speak about are three new ones which have lately 
not come out but been brought to the front, and which I wish to bring 
to your notice. One of them is certainly quite new, and the other two 
are, I think, equally new to many of you. As I have some experiments 
to make in order to show you better how the process of silvering is 
carried on in various ways, I shall proceed with that part first, with 
your permission. The silvering of mirrors has enabled a reflecting 
telescope to be made now of glass instead of speculum metal, and not 
9. Vou. XXIII. 
