198 THE SEVEN FOLLIES OF SCIENCE 



Of course those who have even the slightest knowledge 

 of optics and the construction of optical instruments can 

 never make this mistake, but a very large majority of those 

 whom we meet in daily life know nothing of these things, 

 and unfortunately it does not follow because a boy at 

 school has gone over the section on optics in his Natural 

 Philosophy, that therefore he understands these things. 



If by power we mean the extent to which a lens magnifies 

 any object, then it will be found that the smallest lenses 

 are the most powerful. 



It is a very elementary truth that of two lenses composed 

 of the same material that which has the sharpest curvature 

 to its surfaces will magnify most. Now, on reflection it 

 will be evident to even the least mathematical mind that 

 lenses which have very sharp or '"quick" curves must of 

 necessity be small. Suppose that the curve which bounds 

 the figure of a lens has a radius of half an inch; then it is 

 evident that the largest lens which could be made with 

 this curve would be one inch in diameter and then it would 

 either be a perfect sphere or approaching a plano-convex. 

 Most lenses, however, resemble thin slices cut off the spheres, 

 either making a plano-convex lens or two such slices joined 

 together, making a double convex lens, so that the diameter 

 of the lens is in general much less than the diameter of 

 the curves which form its surface. Therefore we see that all 

 lenses of high power are of necessity small, and when lenses 

 are required of very high power they become so minute that 

 they can be handled only with great difficulty. Indeed, 

 before the modern improvements in the microscope many 

 of the lenses used by scientific men were nothing more than 

 small globules of glass brought to a round form by fusion. 

 And they were the most powerful microscopes then known. 



