44 THE MECHANICAL DESIGN OF MICROSCOPES: 



The development of a mechanical invention which is ultimat-ely 

 required to meet a big demand, usually follows upon well defined 

 lines. At the beginning, when the demand is small, the labour 

 of highly skilled craftsmen is necessary and sufficient for its pro- 

 duction, but later, when the demand has increased, it is found that 

 for efficient production the skilled craftsman is no longer sufficient, 

 but special machinery must be put down to replace him. In other 

 words, artistic production is followed by machine production. 



As an illustration of production in the artistic period, I cannot 

 do better tt.an tell you a story that was told to me some years ago 

 by the late Dr. Czapski, Dr. Czapski upon one occasion visited 

 Hartnack, the famous maker of microscope water-immersion objec- 

 tives. He found him sitting on a stool in front of a window, busily 

 engaged assembling the systems of his objectives with the aid of 

 a, microscope and a test-object. On the table by his side were a 

 lumber of grooved sticks, each filled with a number of a particular 

 lens wanted in a ceitain objective combination. Hartnack, with 

 his great knowledge and skill, was able to look at a critical object 

 and decide from its appearance what lens in a given combination 

 was likely to be responsible for the observed defects. He would 

 then try another and slightly different one in its place. In this 

 way he would try combination after combination, until a satisfactory 

 result was obtained. Occasionally by a fortuitous accident he would 

 obtain an objective much superior in its performance to the general 

 run. These were carefully put on one side, and although Hart- 

 nack charged a uniform price for all his objectives, he was very 

 careful to allow none but serious workers to obtain possession of 

 the best quality lenses. Now Abbe realised that this method of 

 production, making such great demands upon unique knowledge and 

 skill, could not possibly meet the growing world's demand for micro- 

 scope objectives, and therefore that the highly skilled, technical 

 artist must be dispensed with and replaced by mechanical processes 

 capable of producing to a high order of accuracy predetermined 

 elements. This was done, and that success which is now a matter 

 of history, achieved. Some time ago I was discussing this subject 

 with Sir Howard Grubb, and he gave me a remarkable instance 

 from his own experience. He told me that before the war he em- 

 ployed a skilled man to rough out certain lenses by hand at the 

 rate of about a dozen per week. When the war broke out it was 

 realised that something must be done to expedite production, and 

 Sir Howard Grubb invented a special machine, attended by a girl, 

 to psrform the necessary operation. The result was that the girl and 

 the machine turned out more than a thousand of these lenses per 

 week. 



It follows from what has been said that the microscope must 

 meet nc^t only the demands of the user, it must meet al?o those of 

 the manufacturer. I suggest, therefore, that a well designed com- 

 mercial microscope may be defined as one that can be made both 

 accurately and cheaply, and that secures in its use " the greatest 

 happiness of the greatest number." First, it must be a commercial 

 article, one made in great numbers to compete in the markets of 

 the world. Secondly, it must be made accurately and cheaply. 

 These requirements necessitate on the part of the manufacturer 

 specialisation, standardisation, production by repetition machinery 



