ON SOME N.S.W. TAN-SUBSTANCES. 27 



is neglected, lead to a certain mathematical relation between the 

 speed of the wings and the resistance which they experience. Mr. 

 Hargrave finds by his experiment that the observed relation does 

 not exactly coincide with the calculated relation, especially when 

 the wings are associated so as to set great quantities of air in 

 motion* In this case viscosity would have a great effect, and if 

 the formulae employed by Mr. Hargrave had been calculated without 

 taking this viscosity into account, the discrepancy between theory 

 and experiment might be accounted for, amongst others, in this 

 way. 



Mr. Hargrave replied that the viscosity of the air had not been 

 taken into account in his calculations. 



The thanks of the Society were accorded to Mr. Hargrave for 

 his paper. 



List of Drawings. 



Figure 1. Plan of large machine. Scale 3" to the foot. 

 „ 2. Side elevation of large machine. Scale 3" to foot. 

 „ 3. ; End elevation of large machine. Scale 3" to foot. 

 ,, 4. Mean of 6 indicator cards. f Scale, Full size. 

 „ 5. The best of 6 indicator cards. Scale, Full size. 

 ,. 6. Diagram of Forces. 

 „ 7. Half-plans of three Flying-machines, A. B. C. 



Scale, 3" to the foot. 

 „ 8. 24-band Flying-machine. Scale 24" to the foot. 

 ,, 9. Whirling plane. Scale 6" to the foot. 



SOME NEW SOUTH WALES TAN-SUBSTANCES. 

 Part I. 

 By J. H. Maiden, F.R.G.S. 



[Read before the Royal Society of N.S.W., 1 June, 1887.'] 



This paper is the first of a series which I hope to be able to 

 complete, on the Tans or astringents of New South Wales. There 

 is no doubt that there are many barks, (especially of species of 

 Acacia), which contain the tanning principle in quantity sufficient 

 for them to be rendered useful to man, and which are either not 

 in use at all, or are not generally known. It will also be useful 



* Note. — The difference between observation and a rough formula is 

 only noted in the experiment of a plane of 1 sq. ft. area moving at a 

 maximum speed of 10-16 miles per hour. 



