XVill. ABSTRACT OF PROCEEDINGS. 
ABSTRACT OF PROCEEDINGS, AUGUST 4, 1897. 
The General Monthly Meeting of the Society was held at the 
Society’s House, No. 5 Elizabeth-street North, on Wednesday 
evening, August 4th, 1897. 
The President, Henry Deane, M.A., W. Inst. C.E., in the Chair. 
Twenty-nine members and one visitor were present. 
The minutes of the preceding meeting were read and confirmed. 
The following gentlemen were duly elected ordinary members 
of the Society :— 
Boucher, Arthur Sackville, Sydney 
MacDonald, ©. A., Sydney. 
The certificates of two candidates were read for the first time. 
THE FOLLOWING PAPERS WERE READ :— 
1. “The Theory of the Reflecting Extensometer of Prof. Martens,” 
by G. H. Ky1ps, F.R.4.s., Lecturer in Surveying, University 
of Sydney. 
When the extensions measured by this instrument are large, 
the scale-readings require corrections which become considerable 
toward the end of the scale. If ¢ denote the extension resulting 
from applied stress, R the scale-reading, / the width of the prism, 
L the distance between the mirror and scale, w the rotation of the 
prism, and £ the length of the contact piece, then it is shewn that 
oe ma " = (1+ ne sin w F : : tan?) 
The factor following the . may be treated as a correction of the 
approximate expression preceding it. Tables are supplied with 
the arguments & and #. It is shown that the disposition of the 
apparatus, indicated by Prof. Martens, eliminates errors due to 
longitudinal shift or small rotations of the test piece. The best 
disposition and proper adjustment of the apparatus is discussed. 
2. “On the Saccharine and Astringent Exudations of the ‘Grey 
Gum,’ Eucalyptus punctata, D.C., and on a product allied to 
aromadendrin,” by Henry G. Smirn, r.c.s., Technological 
Museum, Sydney. 
