MEETINGS OF SOCIETIES. 531 
the measurement of lines upon the earth’s surface, whether precipitous 
or level. It was stated that the ribbons were eminently suitable in 
ordinary surveying practice, having had the test of considerable expe- 
rience, and that they offered a solution of the difficulty presented in 
obtaining precision in rough country, which hitherto had been con- 
sidered imvossible. The subject was mathematically investigated, and 
the results confirmed by extensive experiments. Various formule and 
tables required in practice were computed, and were embodied in the 
paper. ‘The chief feature of the method of measurement was the appli- 
cation of such tensions to the ribbon as eliminated the effects of its 
suspension when that became necessary. Mr. Knibbs explained that 
the consideration of this part of the subject involved the investigation 
of the elasticity of the ribbons used, and of the application of suitable 
compensating tension to be applied by means of a spring balance. 
Various formule to indicate the amount of this compensating tension 
had, it was stated, been invented for the several conditions occurring in 
practice. 
(2) “Notes on Flying Machines,” by Mr. L. Hargrave. The notes 
consisted of deductions drawn from the close observation of the 
behaviour of about 50 self-supporting flying.machines of weights varying 
from -ounce to four ounces. Sixteen models were exhibited, showing 
features to which Mr. Hargrave attached special significance. Mr. 
Hargrave, although he believed the trochoided plane to be the true 
mechanical power used by birds in flight, thought its acceptance or 
rejection as a scientific truth of trifling importance compared with the 
judicious variation and adjustment of the details of the models, so that 
rules could be laid down for work on a larger scale. It was shown that 
the flying models were identical in principle with the two planes 
trochoided vertically in water and previously described to the society, 
and that the equivalent plane of two radially trochoided wings repre- 
sented one of the vertically trochoided planes ; and the body plane of 
the flying model represented the other. The equivalent plane was 
defined as an imaginary surface trochoided by an imaginary crank and 
connecting rod capable ot throwing a wave equal in section and pitch to 
the mean of the infinite number of waves thrown by the two radially 
trochoided planes: the section of the wave of the equivalent plane was 
a rectangle, that of each wing plane was a sector of a circle. Attention 
was drawn to the fact that existing knowledge on the subject of 
artificial flight was in such an advanced condition that they could now 
see the tho: aghtlessnoss of these who nsed to try their flving-machines 
first of all from an eminence, and how such a method of experimenting 
hindered progress ; and that the daily use of the flying-machine as a 
means of transit would be vrougiy muecu wcarec it puts os sino if 
younger brains than theirs were directed to the improvement of the 
models, as these were nearly as easy to make asa kite, and it was 
observable that a boy would often detect a fault and suggest a remedy 
which older persons failed to see. 
Sydney, Ist July, 1885.—Professor Liversidge in the chair. 
New Members.—Dr. von Lendenfeld, Messrs. H. Deane, Jas. S. 
Marks, and A. W. Munro. 
Papers. —(1) ‘‘ Local vibrations of the earth’s surface,” by Mr. 
H. C. Russell, B.A., F.R.A.S., &e. 
