40 The Stability of Structures 



precedent. For instance, from observation, we find that a 

 structure of certain dimensions has successfully resisted all 

 the gales experienced since its erection; therefore, in building 

 structures in similar positions we cannot go astray in 

 imitating such an example. 



This course^ though one which I believe to be frequently 

 adopted, and with some reason, in small and inexpensive 

 structures, is, where important structures are concerned, 

 both unscientific and unsound. It is no guarantee of the 

 safety of the structure, still less of its economy. 



Notwithstanding the uncertainty as to extreme wind 

 pressures, I believe that, by bringing observation, judgment, 

 and experience to the aid of calculation, the subject can be 

 dealt with in a manner both scientific and logical, disposing 

 of the material to the best advantage, and securing all 

 reasonable safety with the utmost degree of economy. 



To investigate the matter as proposed, it will be necessary 

 to consider a number of points in connection therewith, 

 which for convenience I have classed under four heads, viz.: — 



1. The maximum pressure of the wind at or near the 

 locality of the proposed structure. 



2. The nature of the situation as to shelter or otherwise. 



3. The height of the structure above the ground, and the 

 nature of its construction. 



4. Its value, use, and whether its failure would involve 

 loss of life or damage to adjacent property. 



First. The maximum 'pressure of the wind at or near the 

 locality of the proposed structure. 



Stations for observing and recording the pressure of the 

 wind are usually confined to the Government Observatories. 

 This is the case, I believe, in the Australian colonies. 



As these observatories are usually upon commanding 

 positions, with the anemometer fixed high above the 

 ground, we may safely assume that the records from these 

 points are not likely to be exceeded in other localities. 



The following list gives all the information as to 

 maximum wind pressures that I have been able to collect : — ■ 



Maximum Wind Pressures. 



Per sq. foot. 



Williamstown Old Observatory, Victoria, 1854, 



Ostler's anemometer... ... ... ... 35 lbs. 



Sydney Observatory, N.S.W.^ 65 feet above 



ground ... ... ... ... ... 115 lbs. 



