.s/A' WILLIAM SIEMENS, F.R.S. 133 



<>nlT to support the lines of wires at a given height ? In the first 

 instance he turned his attention to the tripod. The tripod was a 

 strong form, a very stable form, and by means of that con- 

 struction he succeeded in making a strong post. But this con- 

 st niftion was not satisfactory, because each limb of the tripod 

 was not sufficiently strong in itself to stand independently. Each 

 member of the structure required support. These supports had 

 necessarily to be lateral supports, and these lateral supports, while 

 they added to the weight and to the expense, did not contribute 

 to bear the strain that might be applied on the top of the posts. 

 Therefore, he abandoned that form in favour of a tubular con- 

 struction. Now the tube was evidently the right form for bearing 

 a strain in all directions equally, because each part of the material 

 was at the greatest possible distance from the centre ; but a 

 cylindrical tubular form was evidently a bad construction, because 

 it would give an excess of strength near the point of suspension, 

 and a minimum or relatively insufficient strength at the base. 

 Therefore the conclusion he drew from this was that a conical 

 tube would be the best. But, on going minutely into the question, 

 a conical tube did not seem to fulfil these conditions, but a tube of 

 a parabolic form externally was the form which gave the maximum 

 of strength. The drawings on the wall showed the upper portion 

 of such a post to be a wrought-iron tube of that parabolic form 

 which, when a weight was horizontally applied at the top, gave 

 t'qiial deflections in all parts. The next question was, What is 

 the proper thickness of the material of such a tube ? Captain 

 Mallock had just said that the larger the tube and the thinner the 

 metal, the greater would be its strength. He dissented from that 

 entirely. If more stiffness was gained by increasing the diameter 

 at the expense of the metal, the strength was not increased in a 

 tube such as that shown, which had a thickness of metal of about 

 a quarter of an inch, and a diameter of about four inches. If 

 reduced in thickness it would collapse, and collapse with a less 

 weight than the actual tube would bear. If, on the other hand, 

 the diameter was decreased and the thickness of metal increased, 

 it \vuuld break or bend with a less weight. Therefore, there was 

 a point of proportion between diameter and thickness, a propor- 

 tion which gave an absolute maximum of strength. He did not 

 agree with Major Webber in saying that telegraph poles might be 



