Dr. G. J. Stoney on Microscopic Vision. 513 



that are betrayed to us through the spectroscope. In the 

 face of such facts as these it is in vain for biologists to talk 

 as if anyone had at any time seen such a thing in nature 

 as " undifferentiated protoplasm/' or as if any speck of matter 

 that can be seen by the best microscope is other than a body 

 of large size from the molecular standpoint, within which 

 there may be a vast amount of structure and an inconceivable 

 flow and variety of events continually in progress. The 

 finest flagellum of a saprophyte, the tiniest rod in karyokinesis, 

 may, consistently with every lesson taught us through the 

 microscope and by molecular physics, have quite as elaborate 

 a structure as that part of the structure of the limb of a 

 quadruped which can be seen by the human eye. 



Coarse rulings are usually produced by a fan of numerous 

 beams. It is thus that the shape of the bars of which they 

 consist is brought out. But the finest rulings are of the 

 first order, i. e. in their case the fan has been reduced down 

 to two beams. Now the intensity of the light in rulings of 

 this kind follows the law [1 — cos (2irx(g-\-g')[)C)'] *, which is 

 represented by the diagram on p. 511; and the microscopist 

 should constantly bear in mind that every speck or band upon 

 the object which is sufficiently minute to have its image 

 formed exclusively out of rulings of the first order must 

 accordingly have the appearance of a little hillock or little 

 ridge wholly devoid of detail and with blurred outline : and 

 that notwithstanding this there may be any amount of detail, 

 variety of outline, and intricacy of motions present upon the 

 actual object within the limits of the part represented by that 

 speck or band. 



37. Propositions 8 and 9. Cause of bright specks becoming 

 dark ; and Cause why fine detail often seems to shift upon an 

 object. — The finer detail in image C is formed by the inter- 

 lacing of beams that are inclined at a large angle to one 

 another. Let u and u be two such beams in one meridian 

 plane, and let the unbroken lines of fig. 1 represent those 

 wave-surfaces in them which at the instant t are in phase 0. 

 Then it is easy to see that the two undulations reach every 

 point of the planes represented by the dotted lines in the same 

 phase. Hence if minute markings are seen by the ruling 

 produced by these beams cooperating with rulings produced 

 by other pairs of beams which are but little sloped to u and 



* If the two beams are not in the same meridian plane, g+g should be 

 replaced by d, i. e. by the number on scale X which is represented by the 

 length of d, which is the distance asunder in image x of the free ends of 

 g and g'. (See § 34, p. 506.) 



