Feb. 2, 1888] 



NATURE 



32, 



Init inasmuch as part of them may be in a mobile fluid 

 like air, and part of them in a solid like iron or steel, it is 

 convenient to distinguish between their two portions ; 

 and one may think of the air whirls alone as reaching 

 from one piece of iron to another and by their shortening 

 tendency or centrifugal force pulling the two pieces 

 together. 



The arrangement shown in Fig. 31 illustrates the kind 



Fig. 31. — A "shape of the earth" model which, when whirled, exerts a 

 tension along its axis, pulling up the weight attached to it, and a 

 pressure at right angles, by reason of its bulging out. 



of force exerted by a spinning elastic framework along 

 and perpendicular to its axis of rotation. 



One can easily see this effect of a whirl in a tea-cup or 

 inverted bell-jar full of liquid. Stir it vigorously, and 

 leave it. It presses against the walls harder than before, 

 so that if they were elastic they would bulge out with the 

 lateral pressure ; and it sucks down the top or free end of 

 its axis of rotation, producing quite a depression or 



Fig. 32.— -An elastic-walled cylindrical vessel full of liquid hanging from a 

 whirling table, and, by reason of centrifugal force, raising a weight and 

 bulging out laterally when spun, thereby illustrating a tension along the 

 axis of rotation and a pressure in every perpendicular direction. 



hollow against the force of gravity. Or, as a more striking 

 illustration, make the following apparatus. 



Two circular boards joined by a short wide elastic tube 

 or drum : a weight hung to the lower board, the top board 

 hung from a horizontal whirling table, the drum filled with 

 water, and the whole spun round. The weight is raised 

 by the longitudinal tension ; the sides bulge out with the 

 lateral pressure. 



There is no need for the whole vessel to rotate. If the 

 liquid inside rotates, the same effect is produced. 



Imagine now a medium composed of a multitude of 

 such cells with rotating liquid inside : let the cells be 

 either very long, or else be joined end to end so as to 

 make a chain — a series of chains side by side — and you 

 have a picture of a magnetic medium traversed by a field 

 of force. End-boundaries of the field will be dragged 

 together, thus representing magnetic attraction ; while, 

 sideways, the lines of force (axes of whirl) squeeze each 



Attraction. 



Repulsion. 



E.G. 33. — Attraction and repulsion. The tension along the lines of force or 

 axes of rotation drags the one par of poles together ; and the pressure 

 in directions perpendicular to the axis of rotation due to the centrifugal 

 force of the whirls drives the other pa', r apart. 



Other apart, thus illustrating repulsion. This is Clerk- 

 Maxwell's view of an electro-magnetic medium, and of 

 the mode in which magnetic stress, and magnetic 

 attractions and repulsions between bodies, arise. 



Wherever lines of force reach across from one body to 

 another, those bodies are dragged together as if pulled 

 by so many elastics (Fig. 33); but wherever lines of force 

 from one body present their sides to those proceeding 

 from another body, then those bodies are driven apart. 



Oliver J, Lodge. 



(.To be continued.) 



LANGUA GE-REA SON. 



THE inclosed letter on "Reason-Language" waswritten 

 to an American friend, and has been published in 

 an American paper in Chicago. I thought it might 

 possibly interest the readers of Nature^ 

 Oxford, January 22. ^ 



F. Max Muller. 



