Factors of Safety in Mechanics in Animal Structure and in Animal Economy.

Progress, Volume III, Issue I, 1 November 1907, Page 26

Factors of Safety in Mechanics in Animal Structure and in Animal Economy.

Dr S. J. Meltzer recently addressed a lecture on the above subject to the Harvey Society of New York — Meltzer borrows the term " factor of safety " from the mechanical engineer who thus designates the margin of safety required m constructing engines, bridges, houses, and the like If for instance, the tensile strength of boiler steel plates and stay bolts is 60 000 pounds to the square inch, the actual stress which is allowed for the work of the boiler should not be more than 10,000 pounds per square inch for the plate and not more than 6000 pounds per square inch for the stay bolts — which means that the stress to which the plates may be exposed in the boiler should be only one-sixth or one-tenth of the actual strength of the steel. The factors of safety are here said to be six for the plate and ten for the bolts. Tn mechanics, then, it is calculated that the structures should be capable of withstanding not only the stresses of reasonably rxpected maximum loads, but also those of six or seven times such loads. The factor of safety is founded upon finite human ignorance of what might happen, and upon a wise and very praiseworthy desire to provide against such contingencies. Wherefore these factors are oftentimes termed factors of ignorance And, with regard to the human machine, the latter term would seem rather .the preferable one. For this machine is, by comparison with those constructed out of inorganic materials and worked by men, of complexity quite infinite. It is, of course, much more difficult to foretell the possible strain, the stress of environment, accidents, the attacks of parasitic organisms, and the myriad other agencies hurtful to the human machine, many of which we are powerless to prevent, concerning many of which we are in ignorance — ignorance, -we are however proud to say, which is yearly becoming more and more dissipated.