192 Master Minds of Modern Science 



supplemented by experiments on airships in actual flight. 

 Parachutes, windmills, aeroplane carrier ships, and the 

 wind-resistance of planes, spheres, cylinders, and spheroids 

 — all have been made the subjects of tests, and this 

 methodical work has yielded a mass of information of the 

 utmost value to the aircraft industry. 



Yet another department of this wonderful institution 

 is that devoted to Metrology. Here are kept the stan- 

 dards of measurement which are used by us all, and here 

 new standards are devised when these are called for by 

 discoveries of new materials or processes. 



When we talk lightly of so many yards or metres in 

 length, pounds or grammes in weight, seconds or minutes 

 in time, so many degrees of temperature or ohms of elec- 

 trical resistance, do we realize that somewhere there must 

 be an institution capable of making absolutely accurate 

 measurements of these quantities? Many of them are 

 defined by law, and it is of the most vital importance that 

 all should be fixed. Then when one remembers the manu- 

 facturing processes, where precision is required for scien- 

 tific work, it seems doubly important that the standard 

 should be fixed with the greatest possible accuracy. 



At the National Physical Laboratory may be seen a 

 brightly polished bar with faint scratches on its surface. 

 It is a copy of the Imperial standard yard. As most 

 people know, this is the distance between two points 

 marked on a bronze bar kept in Trafalgar Square. 

 Another bar — this of platinum — measures the metre. 

 Against these absolutely accurate measures are tested 

 yards and metres submitted to the Laboratory by 

 commercial firms, Government Departments, and others. 



The actual process of testing is too technical to be 

 described in a short space. It consists in placing the yard 

 to be tested beside the standard yard in a water-bath to 

 keep them both at the same temperature, and then in 

 reading the minute scratches on the official standard yard 



