588 SCIENCE PROGRESS 



subject was treated in a more elegant form by W. R. Bousfield, 

 who showed that the fundamental form was a twisted surface, 

 generated by straight lines, and giving the furrow-slice a uniform 

 rotation proportional to the distance traversed along the length 

 of the mould-board. The best practical British types differ 

 but little from this fundamental form. Their purpose is to 

 invert the slice without breaking it, so that it may stand 

 exposed to the action of the weather over the winter months. 

 In other countries a form of plough in general use is provided 

 with a mould-board in the form of a curved scoop, the action 

 of which is to break and crumble the slice. This form of 

 cultivation is generally used where it is necessary to get the land 

 rapidly into a suitable seed-bed — as, for instance, in parts of 

 America, where the land is frozen throughout the winter, and 

 impossible to cultivate until thawed out in the early spring. 



Varying soil and climatic conditions, together with advances 

 in metallurgy and engineering, have led to a great multiplication 

 in the types of plough on the market, and in the present state 

 of our knowledge it is impossible to say whether many of these 

 patterns are unnecessary or whether soil cultivation is such 

 a complex problem that each soil type demands a distinctive 

 form of implement. 



The economic changes due to the war and the advent of the 

 internal combustion engine are greatly altering modern farming 

 practice. Mechanical traction is rapidly displacing horse 

 traction, and the new conditions are bringing in their wake a 

 whole host of new problems, especially in the domain of soil 

 cultivation. Many fresh patterns of ploughs have been devised 

 suitable for use with tractors, but the basis of the improvement 

 is empirical. At present there is no means of estimating, even 

 approximately, the value of a particular implement except by 

 prolonged practical trials, and even then there is no certainty 

 that the implement will be equally effective on all types, or 

 even limited types, of soils. 



The practice of soil cultivation is, in fact, in a period of 

 transition ; it should be possible to guide its progress by study- 

 ing the factors involved both from the physical and engineering 

 aspects. The directions in which this would profitably be 

 done have been set out in the recent Report on Agricultural 

 Machinery by a Departmental Committee of the Ministry of 

 Agriculture (Cmd. 506, 1920, Stationery Office, is. net). This 

 report emphasises the fact that progress in research as regards 

 tillage implements must largely depend upon the results of 

 investigations into soil physics, and especially the problems 

 of tilth. 



At first it will be necessary to proceed by analytical methods, 

 in order to disentangle the many factors involved. For instance. 



