March 14, 1889] 



NATURE 



461 



The Formation of Ledges on Hill-sides. 



In Nature for February 28, Mr. Ernst draws attention to 

 the formation of these ledges as observed by himself in Caracas. 

 They are probably to be found in many places, if carefully looked 

 for. The following diagram, taken from a photograph, illustrates 

 •one of the most striking instances I know, to be found near 

 Ballantrae, on the Ballantrae-Girvan road, Ayrshire. The 

 ledges, which are very numerous and fairly regular, occur on the 

 western face of a series of low hills, very near to the sea-shore. 



The subsoil is thin and open. The angle of slope ranges from 

 perhaps 30° to 60°, seldom higher. Where the angle is much 

 higher, the soil slips away bodily, and the grass with it, leaving 

 a bare space ; indeed, at one point of the road the precipitated 

 soil forms readily visible mounds at the base of the cliff. 



The whole locality is very unfavourable to earthworms, and 

 I agree with Mr. Ernst that the earthworm theory must, as far 

 as any practical effect is concerned, be surrendered. 



On the other hand, had the ridges been due to anything like 

 glacier action, as Mr. Ernst suggests, I should have expected 



1 



■detrital mounds below the ledges at the foot of each slope. 

 These, however, do not occur, and the soil meets the narrow 

 strip of plain with surprising angular sharpness. 



It seems clear that the ledges owe their origin to the action of 

 rain-water, which would naturally penetrate below the surface 

 covering of grass, and dissolve with comparative rapidity portions 

 of the porous soil below. The grass layer would eventually have 

 nothing to support it in places, and would collapse to a lower 

 level. The effect of collapse, supposing the layer to hold toge- 

 ther, would necessarily be a wrinkle or ledge at right angles to 

 the ground slope. Edmund J. Mills. 



Glasgow, March 4. 



Weight, Mass, and Force. 



If Mr. Gray, as in his teaching he no doubt unconsciously 

 often does, will always say "force of a pound" instead of 

 "weight of a pound" when he wishes to express the force of 

 attraction of the Earth on a pound weight, there will be no 

 divergence between his theoretical instruction and the language 

 ■of practical men and of everyday life. 



But to the majority the expression "weight of a pound" will 

 always call up the mental picture of a " pound weight," so that 

 the idea of the mass of a pound and of the force with which it 

 is attracted by the earth cannot be dissociated in the use of the 

 word " weight." 



Supposing, however, we accept the definition of the "weight 

 of a body " as never meaning anything else than the " force with 

 which the earth attracts the body," how are we to interpret "the 

 weight of the Sun, of the Moon, of Jupiter, &c.," and what is 

 Ae " weight of the Earth ? " 



As Mr. Gray declines my previous challenge, will he con- 

 descend to point out the fallacy in the following argument? 

 "The weight of the Moon being the force with which the Moon 

 is attracted by the Earth, ergo, by the law that Action and 

 Reaction are equal and opposite, the weight of the Earth is equal 

 to the weight of the Moon." 



With our present system of instruction in elementary theo- 

 retical dynamics we run the risk of wasting our time on a 

 mechanics which is as unreal as is the mediaeval Greek grammar 

 taught in our schools, a grammar that was never vernacular even 

 in the palmiest days of Attic literature. 



The warning note in the introduction to "Numerical Examples 

 in Practical Mechanics," by R. G. Blaine, is well timed and 

 deserves careful attention. A. G. Greenhill. 



The Inheritance of Acquired Characters. 



A VERY Strong a frioH objection to the line on which most 

 experiments on the inheritance of acquired characters are carried 

 on is the following. These experiments involve mutilation ; and 

 a tendency to transmit characters so produced would, consider- 

 ing that every accident or fight produces some slight mutilation, 

 involve the animals in a process of degeneration. Hence the 

 tendency to transmit the characters acquired by mutilation 

 would be constantly bred out by natural selection. But a tend- 

 ency to transmit characters acquired by habit in youth rests on 

 quite another basis, and would tend to the conservation of the 

 race. 



I do not know if observations have been made on the physique 

 of the offspring of persons engaged in trades where apprentice- 

 ship be.;jins before puberty : they would be most valuable. 



But the following case seems to me to be thoroughly to the 

 point. A. B. is modeiately myopic and very astigmatic in the 

 left eye ; extreirely myopic in the right. As the left eye gave 

 such bad images for near objects, he was compelled in childhood 

 to mask it, and acquired the habit of leaning his head on his 

 left arm for writing, so as to blind that eye ; or of resting the 

 left temple and eye on the hand, with the elbow on the table. 

 At the age of fifteen the eyes were equalized by the use of 

 suitable spectacles, and he soon lost the habit completely and 

 permanently. He is now the father of two children — a boy and 

 a girl— whose vision (tested repeatedly and fully) is emmetropic 

 in both eyes, so that they have not inhe rited the coni;enital 

 optical defect of their father. All the same, they both have 

 inherited his early ac j.ired habit, and need constant watchful- 

 ness to prevent their hiding the left eye, when writing, by resting 

 the head on the left fore-arm or hand. Imitation is here quite 

 out of the question. 



Considermg that every habit involves changes in the 

 proportional development of the muscular and osseous sys- 

 tems, and hence, prolably, of the nervous system also, the 

 importance of inherited habits, natural or acquired, cannot be 



