I should like to thank Mr. Hafner for his paper on “ Safe Mechanisms ” published in the May Journal (p. 273). There is much scope for thought and invention along the lines he suggests and such thought will result in increased safety.

In Section 3.1 on page 276 “ Safety Standard,” it is suggested that accident statistics should be quoted on an hourly basis and not per mile. A man expects to live three score years and ten; it is, therefore, the risk of spending a proportion of this time in a given occupation which is significant. It is then possible to compare the relative risks of lying in bed, train travel, air travel, space travel and so on.