Phillips. — On Spiders as Engineers. 603 



webs I did not see a single spider, so I cannot tell to which 

 order it belonged. I do not think it was Argyroneta aqnatica, 

 but rather an ordinary geometric spider. The bridge-struc- 

 tures and land-stays were evidently for the purpose of allow- 

 ing the animal to pass quickly from side to side of the drain. 

 With regard to the shore-stays beneath the roadway, I do 

 not remember seeing such stays used in any of our suspension 

 bridges. I suppose it is considered that they would only add 

 weight to the structure. I fancy in this that strength is 

 sometimes sacrified to lightness. 



[Note. — Mr. T. W. Kirk has called my attention to the 

 Hobson Street suspension bridge, Wellington, in which there 

 are shore-stays beneath the roadway, and he informs me that 

 they are not uncommon, only in low suspension bridges they 

 form a danger in time of flood. Mr. H. B. Kirk, M.A., also 

 informs me that across the Kaihu Eiver, at Opanaki, Darga- 

 ville, there is a small bridge with both upstream and down- 

 stream stays.] 



Immediately on the land-side of each bridge a geometric 

 prey-net was always suspended, which makes me think that 

 the bridge and the two land-webs belonged to the one spider. 

 There was no reason, of course, why one spider should not 

 have hung eight or ten prey-nets, and constructed two or 

 three bridges. My sole reason for writing this paper is to call 

 attention to the fact that we should stay our high bridges 

 more than we do, and as far out as we possibly can, by pillars 

 lessening in height, if necessary, to each shore. It may have 

 been that if the Tay Bridge had been properly stayed, as these 

 animals stay their structures, especially in the direction of the 

 greatest wind-force, the late fatal collapse and loss of life there 

 would not have happened. Of that I feel convinced. The enor- 

 mous stays of spiders' webs must strike any person. Would 

 it not, therefore, be a safe plan for our engineers to construct 

 intermediate side-pillars up and down stream if necessary, 

 according to the direction of the greatest wind-force ; stay 

 these pillars from the shore, and the bridge from the pillars ? 

 Might this principle not be applied even now to the great 

 cantilever bridge over the Forth, or to Brooklyn Suspension 

 Bridge in New York, or to Clifton Suspension Bridge? A 

 couple of stays would greatly strengthen any bridge. Of what 

 use would our tall ship-masts be without their side-stays ? The 

 two constructions are not analogous, I know, but the principle 

 is almost the same. The vibration of the Brooklyn Suspension 

 Bridge is so great that the trains are always drawn over it by 

 ropes ; it is not safe to allow the engines to drag them. The 

 use of stays might reduce this vibration. 



