436 AUTO-SIGHTS, 
found from the equation: 
TP 
fcan ? - TD 
and TF 
TD gin y 
sin (y+a) 
TE + TF 
Finally it is assumed that TO =--- 
It will be noticed that I have taken GT and GC instead of ST and 
SC as the ranges to T and C, and that I have calculated from its 
sine instead of from its tangent. But this method though unusual, 
can only tend to greater accuracy. 
NOTE BY COLONEL SIR G. S. CLARKE, K.C.M.G., F.R.S., R.E. 
Superintendent of the ~Royal Carriage "Factory . 
When a new adjunct of Coast Defence is placed in the hands of the 
Royal Artillery, I think it is undesirable that confidence should be 
shaken at the outset. If a dog obtains a bad name, we know what 
follows, and should a presuming and incompetent mongrel thrust 
itself upon the notice of the very “ fierce dogs ” of the Garrison Artill¬ 
ery a tragedy must inevitably be enacted. For this reason only I ven¬ 
tured to reply to the excellent paper of Colonel H. S. S. Watkin, C.B.,* 
and I now offer a few remarks on Major Hopkins’s able analysis of 
one probable source of error which as I have already stated “ any auto¬ 
sight inventor must evidently face.” 
Major Hopkins has quite correctly calculated the errors arising from 
an inclination of the axis of the mounting although, as Professor 
Greenhill points out, the process is somewhat unnecessarily laborious. 
I take exception, however, to the claim that this paper is “ a step to¬ 
wards a solution of a problem which is of the greatest importance to 
Garrison Gunners.” It seems to me to be an alarming but perfectly 
fair statement of a serious source of error unaccompanied by the ves- 
tage of a hint as to how that error may be met. In designing an 
auto-sight for service use, one of the earliest measures I took was to 
investigate fully the errors due to non-verticality of pivot. The 
formula which Professor Greenhill gives was the one adopted for the 
purpose, and it was evident from the first that (i). Verticality must be 
attained in the original laying of the cast-iron pedestals which I intro¬ 
duced in order to secure rigidity; or (2) means of subsequent 
adjustment must be provided; or (3) the sight itself must be capa- 
• R.A.I. “ Proceedings ”, Vol. XXV., No. C, “ Automatic Sighting.” By Colonel H. S. S. 
Watkin, c.a., R.A. 
