1881.] 



The Action of Cutting Tools. 



127 



escape into the body cavity and make their exit by several pores placed 

 close together, and symmetrically, on each side in the pallial groove ; 

 oviducts apparently being absent. I have not any specimens of the 

 species he mentions as possessing this peculiarity {e.g., Chiton mar- 

 moreus and ruber), so have not been able to test his observations by 

 means of sections. 



I hope to be able to give a fuller account of these and other points in 

 the anatomy of Chiton at some future period, for the preparation of 

 which it will be necessary to obtain some fresh specimens. 



VJ. " The Action of Cutting Tools." By A. Mallock. Com- 

 municated by Lord Rayleigh, F.R.S. Received Novem- 

 ber 4, 1881. 



The action of cutting tools has not often been treated from a theo- 

 retical point of view ; in fact I only know of two papers on the sub- 

 ject, one by Professor Willis and the other by Mr. Babbage. Of 

 these Professor Willis's paper is purely geometrical, showing what 

 angles the edges of tools may make with one another if the cutting- 

 angles are to be such as experience shows to answer best. Mr. 

 Babbage, on the other hand, does not enter at all on the question of 

 the shape of the tool, but by making certain assumptions as to the 

 relation between the dimension of the shaving removed by a tool and 

 the work required to remove it, he deduces some results showing how 

 to remove a given amount of material most economically. His con- 

 clusions cannot be considered correct, nor do they agree with experi- 

 ence (see Note 1). I do not attempt in the following paper to give 

 any dynamical investigation of the action of tools, in fact it would be 

 almost impossible to do so without a more extended knowledge of the 

 laws which govern the strains in bodies subjected to large forces, 

 but merely to classify the various actions which observation shows to 

 be caused by the progress of the tool, and to quantify approximately 

 the work expended in each. For this purpose, shavings from a great 

 variety of substances were examined both in the course of their forma- 

 tion (by a microscope attached to the toolholder) and after they were 

 removed. 



Among the substances examined may be mentioned four or five 

 samples of wrought iron, and as many of steel, cast iron, gun metal, 

 brass, copper, lead, zinc, hard parafhn, soap, and clay. 



This last-mentioned substance was found ' extremely useful in 

 examining the formation of the shavings, for by altering the amount 

 of water it contained its behaviour under the tool could be made to 



