126 Transactions of the Society. 



can be designed which will fulfil all the obligations of medical, 

 biological, petrological, metallurgical, and chemical science, and be 

 adapted for photo-micrographical work. 



That certain difficulties have to be overcome is undeniable, 

 but none of these appears likely to be insuperable. It would be 

 presumptuous on my part to enter into the details involved in 

 my proposal, but perhaps I may be allowed a few suggestions 

 derived from my experience in manufacture generally, as these 

 may possibly conduce to economy in construction, if nothing else. 



That the stand be designed not as a concrete whole, but so as to- 

 admit of successive additions of other standard parts as required. 



That it should be recognized that the optical parts of the 

 microscope cannot be standardized except as regards their parts- 

 fitting to the stand. 



That all fittings, other than optical, be standardized. 



That each part of the microscope be made of the material 

 best suited to the strains and wear it has to undergo. 



That the design should aim at simplicity, a balance of the 

 moving body in all positions, perfect rigidity, uniformity of move- 

 ment round the arc traversed by the moving body, and artistic 

 finish. It should not require clamping, which is likely to disturb 

 adjustments, and must to some extent distort a delicate instrument. 



The manufacture should be carried out by precision tools and 

 precision grinding to limit-gauges, so that all the parts of all 

 instruments will be interchangeable. 



Kegarding rigidity and materials, it may be noted that brass, 

 the material usually employed heretofore, has a tensile of from 

 12-5 to 21 tons per square inch, and elongation of from 28-65 p.c, 

 while aluminium-bronze and rubel-bronze have tensiies of 43 tons, 

 with only 12 '5 p.c. elongation; these bronzes appear more suitable 

 material for the stand than brass to secure rigidity. 



A little book, "Metals and Alloys," published in 1918 by the 

 Metal Industry, 33 Bedford Street, Strand, gives information 

 regarding some 500 metals and alloys, which may be found useful. 

 Attention may also be called to die-casting, which, though more 

 expensive than ordinary brass-founding, produces castings in 

 unlimited number of identical form, of a close texture, and requiring 

 little or no machining. There are several firms in London die- 

 casting, and if in time this method can be applied to hard material, 

 it is certain that its introduction to microscope manufacture would 

 conduce materially both to standardization and economy. 



In conclusion, I may remark that you cannot manufacture unless 

 you have standards, but you cannot have standards unless you use 

 precise methods and tools, and that you cannot have a really good 

 instrument at a reasonable price unless you manufacture. 



