3 o6 SCIENCE PROGRESS 



country to Sir Joseph Whitworth, who demonstrated very clearly the advantages of 

 the use of gauges for accurate mechanical work. By means of a micrometer or 

 some other form of gauge, a workman could fashion his work to the desired degree 

 of accuracy. The next step was the introduction of limit gauges. The workman 

 is given two gauges of fixed dimensions— one a little bigger than is required for 

 the finished work, and the other a little smaller, and all he has to do is to turn his 

 work until the larger gauge will go over it, making sure that he has not ground it 

 so far that the smaller gauge will go over. The difference between the sizes of the 

 two gauges is known as the tolerance. It should be as great as the nature of the 

 work will permit, and varies from a ten-thousandth of an inch in watchmaking to 

 the "sloppy fit" of a perambulator wheel. As a matter of fact, limit gauges are 

 at present only made for the finer classes of work, and it is extremely desirable 

 that their use should be extended to cases in which quite coarse tolerances are 

 permissible. Limit-gauging applies specially to, and is, indeed, essential for, the 

 production of strictly interchangeable parts. Previous to the war the gauges used 

 in this country were in a very bad state ; they were inaccurate in themselves and 

 differed enormously from one another. Indeed, when the demand arose in 191 5 

 for interchangeable parts to be made in different shops for the production of 

 munitions, it was found that the best make of English gauges had errors many 

 times larger than the tolerances called for, and that the average gauge made in 

 the tool-rooms of English firms had errors twenty to thirty times these tolerances. 

 Although experience led to the tolerance being trebled, a great deal of improve- 

 ment was obviously needed to get quantities of gauges of the required accuracy. 

 This work was carried out by the National Physical Laboratory, which designed 

 many ingenious testing-machines capable of accurate and speedy use in the 

 workshops — notably a projection apparatus for examining screw-threads. The 

 importance of work of this character may be judged from the fact that, just 

 before the armistice, 10,000 inspection gauges were being produced per week, and 

 of an accuracy at least equal to those manufactured in other parts of Europe. 



In spite of their war experience, it seems that many manufacturers are now 

 going back to their old methods, while others {e.g., the Engineer's Small Tools 

 Manufacturers' Association of Sheffield) were never converted. It seems clear, 

 therefore, that it is only by educating the younger school of engineers that out-of- 

 date, uneconomical methods of production can be finally abolished. This work 

 has already been taken in hand by Dr. Shaw at Nottingham, and by Prof. Ripper 

 and Mr. Bolton at Sheffield. It is to be hoped that their efforts to found depart- 

 ments of Metrology may meet with continued success, and not dwindle to nothing 

 through the indifference of the manufacturers who are so acutely concerned. 



