40 THE WORLD MACHINE 



this long and wondrous march of the intellect, with no hint of 

 the difficulty, no inspiring presentation of the struggle, no 

 awakening to the splendour of the conquest. 



It is perhaps that we lack an adequate measure of the feat. 

 But as the astronomer, unable like the surveyor to carry his 

 chain to the moon, may yet calculate its distance from measures 

 of its parallax, so perhaps by recourse to analogy, the parallax 

 of the mind, we may find a help. 



Swift, in his classical tale, imagines a race of elfish men so 

 small that hundreds of them may climb about over his body. 

 Let us try to conceive of a race somewhat ten thousand times 

 smaller that is, a race which has the same relation in stature 

 to us as the diameter of the earth to an average man. It 

 chances that within the last forty years we have come to know 

 that beings of these ultra-microscopic dimensions actually 

 exist : the minute fungi which, for good and evil, play so over- 

 shadowing a part in our daily lives the bacteria. It is a 

 somewhat curious fact that, with the perfection of oil-immer- 

 sions, anastigmatics and their like, the eye is now able to 

 perceive and study microbian races of just the proportion we 

 seek. It would require about eight million men of average 

 height, one standing on another's head, to equal a diameter of 

 the earth. On the outermost fringe of visibility a modern 

 microscope shows objects which stand in the same proportion 

 to man. 



It is a little difficult to form a vivid mental presentation of 

 just what this relationship means. The naked eye is puzzled 

 to detect points set much closer than a hundred to the inch ; 

 two or three hundred dots to the inch is for most eyes a con- 

 tinuous line. This is about a fine hair's-breadth. The unit of 

 microscopic measures is the micron, marked with the Greek 

 letter /*, and these run 25,000 to the inch. The lower limits of 

 visibility of present-day microscopes is from a quarter to a 

 seventh of a micron. Doubtless there are living beings some- 

 what smaller ; but a bacillus whose body is of these dimensions 

 that is, about the hundred thousandth part of an inch is 

 the smallest thing we know of alive, and it is the smallest thing 

 that the human eye has ever seen. An average human being 

 is very closely eight million times this in height. 



Bacilli are, as we are learning slowly to know, organisms of 

 an unsuspected complexity. They vary too in size, in shape, 



