132 SECTIONAL ADDRESSES. 



any previously known is soon embodied in an engineering instrument 

 carefully designed and manufactured for sale at a price which makes it 

 available to every physicist for use in further research. Thus modern 

 research in physics and chemistry is carried out with accurate apparatus 

 which would be available only at a prohibitive price if it had been made 

 for the particular research alone. The assemblage of apparatus used in 

 a modern research is sometimes like an engineering installation, and is 

 in marked contrast with the cruder, home-made apparatus, designed ad hoc, 

 which was common when some of us were students. 



The closer the intercourse between the physicist, the chemist and the 

 engineer the greater will be the fertility in invention and the faster the 

 economic progress. The physicist working continually in a laboratory 

 where everything is specially designed to facilitate accuracy of measure- 

 ment and to eliminate disturbance, is apt to forget how artificial his 

 working conditions really are, and that before any of his beautiful experi- 

 ments can have a practical application in industry a great deal of invention 

 is required. As an example of successful invention involving an accurate 

 measurement to be made under practical conditions unsuitable to accuracy, 

 I may cite the Barr & Stroud Range-finder, which was invented by two 

 young professors in this University in the days when it was the Yorkshire 

 College. The problem consisted in measuring with great accuracy, say 

 to a second of arc, the small angle subtended at a distant target by a short 

 fixed base placed at the observer. At the time when this invention was 

 made, some forty years ago, the only scientist who normally measured 

 angles to seconds of arc was the astronomer with his large telescopes 

 mounted on great concrete foundations, with graduated circles from 

 three to six feet diameter and microscopes to read the scales. It seemed 

 therefore impossible to contemplate the measurement of angles with 

 anything like equal accuracy on board a rolling ship and with no expert 

 operator. Yet the two inventors, seeing an advertisement in the pages of 

 Engineering announcing competitive trials of range-finders to be held by the 

 War Office, took this seemingly impossible task in hand. There was little 

 time to spare. The first instrument was designed in outline in a week 

 and much of the subsequent success is attributable to the sound physical 

 principles underlying this design and to the very ingenious design of all 

 the constructional details, due to the happy combination of an engineer 

 and a physicist both of whom were men of imagination with a flair for 

 invention. Their range-finder was constructed in the University buildings 

 and, to indicate the amount of time that was available, the final adjust- 

 ment of the instrument was made on a star from the railway platform at 

 Rugby on the way to the trials at Aldershot. 



During the trials the instrument worked well at first, but after the sun 

 came out it commenced to read ' as thousands of yards ranges which were 

 palpably a few hundred ' and the inventors discovered that their beautiful 

 angle measurer was also a thermometer and a sunshine recorder combined. 

 They were not surprised to have it rejected, and they might actually have 

 abandoned it entirely if they had not been asked by the Admiralty some 

 time later to submit an instrument for naval use. Then followed ten 

 years of most patient struggle against physical and engineering difficulties, 

 not to mention financial difficulties, for the inventors acted as their own 



